at the moment), by linking the kernel to a GPL-ed ROM module
provided by the hypervisor.
-config LGUEST_GUEST
- bool "Lguest guest support"
- select PARAVIRT
- depends on !X86_PAE
- help
- Lguest is a tiny in-kernel hypervisor. Selecting this will
- allow your kernel to boot under lguest. This option will increase
- your kernel size by about 6k. If in doubt, say N.
+source "arch/x86/lguest/Kconfig"
+
endif
config ACPI_SRAT
# Xen paravirtualization support
core-$(CONFIG_XEN) += arch/x86/xen/
+# lguest paravirtualization support
+core-$(CONFIG_LGUEST_GUEST) += arch/x86/lguest/
+
# default subarch .h files
mflags-y += -Iinclude/asm-x86/mach-default
--- /dev/null
+config LGUEST_GUEST
+ bool "Lguest guest support"
+ select PARAVIRT
+ depends on !X86_PAE
+ help
+ Lguest is a tiny in-kernel hypervisor. Selecting this will
+ allow your kernel to boot under lguest. This option will increase
+ your kernel size by about 6k. If in doubt, say N.
--- /dev/null
+obj-y := i386_head.o boot.o
--- /dev/null
+/*P:010
+ * A hypervisor allows multiple Operating Systems to run on a single machine.
+ * To quote David Wheeler: "Any problem in computer science can be solved with
+ * another layer of indirection."
+ *
+ * We keep things simple in two ways. First, we start with a normal Linux
+ * kernel and insert a module (lg.ko) which allows us to run other Linux
+ * kernels the same way we'd run processes. We call the first kernel the Host,
+ * and the others the Guests. The program which sets up and configures Guests
+ * (such as the example in Documentation/lguest/lguest.c) is called the
+ * Launcher.
+ *
+ * Secondly, we only run specially modified Guests, not normal kernels. When
+ * you set CONFIG_LGUEST to 'y' or 'm', this automatically sets
+ * CONFIG_LGUEST_GUEST=y, which compiles this file into the kernel so it knows
+ * how to be a Guest. This means that you can use the same kernel you boot
+ * normally (ie. as a Host) as a Guest.
+ *
+ * These Guests know that they cannot do privileged operations, such as disable
+ * interrupts, and that they have to ask the Host to do such things explicitly.
+ * This file consists of all the replacements for such low-level native
+ * hardware operations: these special Guest versions call the Host.
+ *
+ * So how does the kernel know it's a Guest? The Guest starts at a special
+ * entry point marked with a magic string, which sets up a few things then
+ * calls here. We replace the native functions various "paravirt" structures
+ * with our Guest versions, then boot like normal. :*/
+
+/*
+ * Copyright (C) 2006, Rusty Russell <rusty@rustcorp.com.au> IBM Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
+ * NON INFRINGEMENT. See the GNU General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+#include <linux/kernel.h>
+#include <linux/start_kernel.h>
+#include <linux/string.h>
+#include <linux/console.h>
+#include <linux/screen_info.h>
+#include <linux/irq.h>
+#include <linux/interrupt.h>
+#include <linux/clocksource.h>
+#include <linux/clockchips.h>
+#include <linux/lguest.h>
+#include <linux/lguest_launcher.h>
+#include <linux/lguest_bus.h>
+#include <asm/paravirt.h>
+#include <asm/param.h>
+#include <asm/page.h>
+#include <asm/pgtable.h>
+#include <asm/desc.h>
+#include <asm/setup.h>
+#include <asm/e820.h>
+#include <asm/mce.h>
+#include <asm/io.h>
+
+/*G:010 Welcome to the Guest!
+ *
+ * The Guest in our tale is a simple creature: identical to the Host but
+ * behaving in simplified but equivalent ways. In particular, the Guest is the
+ * same kernel as the Host (or at least, built from the same source code). :*/
+
+/* Declarations for definitions in lguest_guest.S */
+extern char lguest_noirq_start[], lguest_noirq_end[];
+extern const char lgstart_cli[], lgend_cli[];
+extern const char lgstart_sti[], lgend_sti[];
+extern const char lgstart_popf[], lgend_popf[];
+extern const char lgstart_pushf[], lgend_pushf[];
+extern const char lgstart_iret[], lgend_iret[];
+extern void lguest_iret(void);
+
+struct lguest_data lguest_data = {
+ .hcall_status = { [0 ... LHCALL_RING_SIZE-1] = 0xFF },
+ .noirq_start = (u32)lguest_noirq_start,
+ .noirq_end = (u32)lguest_noirq_end,
+ .blocked_interrupts = { 1 }, /* Block timer interrupts */
+};
+static cycle_t clock_base;
+
+/*G:035 Notice the lazy_hcall() above, rather than hcall(). This is our first
+ * real optimization trick!
+ *
+ * When lazy_mode is set, it means we're allowed to defer all hypercalls and do
+ * them as a batch when lazy_mode is eventually turned off. Because hypercalls
+ * are reasonably expensive, batching them up makes sense. For example, a
+ * large mmap might update dozens of page table entries: that code calls
+ * paravirt_enter_lazy_mmu(), does the dozen updates, then calls
+ * lguest_leave_lazy_mode().
+ *
+ * So, when we're in lazy mode, we call async_hypercall() to store the call for
+ * future processing. When lazy mode is turned off we issue a hypercall to
+ * flush the stored calls.
+ */
+static void lguest_leave_lazy_mode(void)
+{
+ paravirt_leave_lazy(paravirt_get_lazy_mode());
+ hcall(LHCALL_FLUSH_ASYNC, 0, 0, 0);
+}
+
+static void lazy_hcall(unsigned long call,
+ unsigned long arg1,
+ unsigned long arg2,
+ unsigned long arg3)
+{
+ if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE)
+ hcall(call, arg1, arg2, arg3);
+ else
+ async_hcall(call, arg1, arg2, arg3);
+}
+
+/* async_hcall() is pretty simple: I'm quite proud of it really. We have a
+ * ring buffer of stored hypercalls which the Host will run though next time we
+ * do a normal hypercall. Each entry in the ring has 4 slots for the hypercall
+ * arguments, and a "hcall_status" word which is 0 if the call is ready to go,
+ * and 255 once the Host has finished with it.
+ *
+ * If we come around to a slot which hasn't been finished, then the table is
+ * full and we just make the hypercall directly. This has the nice side
+ * effect of causing the Host to run all the stored calls in the ring buffer
+ * which empties it for next time! */
+void async_hcall(unsigned long call,
+ unsigned long arg1, unsigned long arg2, unsigned long arg3)
+{
+ /* Note: This code assumes we're uniprocessor. */
+ static unsigned int next_call;
+ unsigned long flags;
+
+ /* Disable interrupts if not already disabled: we don't want an
+ * interrupt handler making a hypercall while we're already doing
+ * one! */
+ local_irq_save(flags);
+ if (lguest_data.hcall_status[next_call] != 0xFF) {
+ /* Table full, so do normal hcall which will flush table. */
+ hcall(call, arg1, arg2, arg3);
+ } else {
+ lguest_data.hcalls[next_call].eax = call;
+ lguest_data.hcalls[next_call].edx = arg1;
+ lguest_data.hcalls[next_call].ebx = arg2;
+ lguest_data.hcalls[next_call].ecx = arg3;
+ /* Arguments must all be written before we mark it to go */
+ wmb();
+ lguest_data.hcall_status[next_call] = 0;
+ if (++next_call == LHCALL_RING_SIZE)
+ next_call = 0;
+ }
+ local_irq_restore(flags);
+}
+/*:*/
+
+/* Wrappers for the SEND_DMA and BIND_DMA hypercalls. This is mainly because
+ * Jeff Garzik complained that __pa() should never appear in drivers, and this
+ * helps remove most of them. But also, it wraps some ugliness. */
+void lguest_send_dma(unsigned long key, struct lguest_dma *dma)
+{
+ /* The hcall might not write this if something goes wrong */
+ dma->used_len = 0;
+ hcall(LHCALL_SEND_DMA, key, __pa(dma), 0);
+}
+
+int lguest_bind_dma(unsigned long key, struct lguest_dma *dmas,
+ unsigned int num, u8 irq)
+{
+ /* This is the only hypercall which actually wants 5 arguments, and we
+ * only support 4. Fortunately the interrupt number is always less
+ * than 256, so we can pack it with the number of dmas in the final
+ * argument. */
+ if (!hcall(LHCALL_BIND_DMA, key, __pa(dmas), (num << 8) | irq))
+ return -ENOMEM;
+ return 0;
+}
+
+/* Unbinding is the same hypercall as binding, but with 0 num & irq. */
+void lguest_unbind_dma(unsigned long key, struct lguest_dma *dmas)
+{
+ hcall(LHCALL_BIND_DMA, key, __pa(dmas), 0);
+}
+
+/* For guests, device memory can be used as normal memory, so we cast away the
+ * __iomem to quieten sparse. */
+void *lguest_map(unsigned long phys_addr, unsigned long pages)
+{
+ return (__force void *)ioremap(phys_addr, PAGE_SIZE*pages);
+}
+
+void lguest_unmap(void *addr)
+{
+ iounmap((__force void __iomem *)addr);
+}
+
+/*G:033
+ * Here are our first native-instruction replacements: four functions for
+ * interrupt control.
+ *
+ * The simplest way of implementing these would be to have "turn interrupts
+ * off" and "turn interrupts on" hypercalls. Unfortunately, this is too slow:
+ * these are by far the most commonly called functions of those we override.
+ *
+ * So instead we keep an "irq_enabled" field inside our "struct lguest_data",
+ * which the Guest can update with a single instruction. The Host knows to
+ * check there when it wants to deliver an interrupt.
+ */
+
+/* save_flags() is expected to return the processor state (ie. "eflags"). The
+ * eflags word contains all kind of stuff, but in practice Linux only cares
+ * about the interrupt flag. Our "save_flags()" just returns that. */
+static unsigned long save_fl(void)
+{
+ return lguest_data.irq_enabled;
+}
+
+/* "restore_flags" just sets the flags back to the value given. */
+static void restore_fl(unsigned long flags)
+{
+ lguest_data.irq_enabled = flags;
+}
+
+/* Interrupts go off... */
+static void irq_disable(void)
+{
+ lguest_data.irq_enabled = 0;
+}
+
+/* Interrupts go on... */
+static void irq_enable(void)
+{
+ lguest_data.irq_enabled = X86_EFLAGS_IF;
+}
+/*:*/
+/*M:003 Note that we don't check for outstanding interrupts when we re-enable
+ * them (or when we unmask an interrupt). This seems to work for the moment,
+ * since interrupts are rare and we'll just get the interrupt on the next timer
+ * tick, but when we turn on CONFIG_NO_HZ, we should revisit this. One way
+ * would be to put the "irq_enabled" field in a page by itself, and have the
+ * Host write-protect it when an interrupt comes in when irqs are disabled.
+ * There will then be a page fault as soon as interrupts are re-enabled. :*/
+
+/*G:034
+ * The Interrupt Descriptor Table (IDT).
+ *
+ * The IDT tells the processor what to do when an interrupt comes in. Each
+ * entry in the table is a 64-bit descriptor: this holds the privilege level,
+ * address of the handler, and... well, who cares? The Guest just asks the
+ * Host to make the change anyway, because the Host controls the real IDT.
+ */
+static void lguest_write_idt_entry(struct desc_struct *dt,
+ int entrynum, u32 low, u32 high)
+{
+ /* Keep the local copy up to date. */
+ write_dt_entry(dt, entrynum, low, high);
+ /* Tell Host about this new entry. */
+ hcall(LHCALL_LOAD_IDT_ENTRY, entrynum, low, high);
+}
+
+/* Changing to a different IDT is very rare: we keep the IDT up-to-date every
+ * time it is written, so we can simply loop through all entries and tell the
+ * Host about them. */
+static void lguest_load_idt(const struct Xgt_desc_struct *desc)
+{
+ unsigned int i;
+ struct desc_struct *idt = (void *)desc->address;
+
+ for (i = 0; i < (desc->size+1)/8; i++)
+ hcall(LHCALL_LOAD_IDT_ENTRY, i, idt[i].a, idt[i].b);
+}
+
+/*
+ * The Global Descriptor Table.
+ *
+ * The Intel architecture defines another table, called the Global Descriptor
+ * Table (GDT). You tell the CPU where it is (and its size) using the "lgdt"
+ * instruction, and then several other instructions refer to entries in the
+ * table. There are three entries which the Switcher needs, so the Host simply
+ * controls the entire thing and the Guest asks it to make changes using the
+ * LOAD_GDT hypercall.
+ *
+ * This is the opposite of the IDT code where we have a LOAD_IDT_ENTRY
+ * hypercall and use that repeatedly to load a new IDT. I don't think it
+ * really matters, but wouldn't it be nice if they were the same?
+ */
+static void lguest_load_gdt(const struct Xgt_desc_struct *desc)
+{
+ BUG_ON((desc->size+1)/8 != GDT_ENTRIES);
+ hcall(LHCALL_LOAD_GDT, __pa(desc->address), GDT_ENTRIES, 0);
+}
+
+/* For a single GDT entry which changes, we do the lazy thing: alter our GDT,
+ * then tell the Host to reload the entire thing. This operation is so rare
+ * that this naive implementation is reasonable. */
+static void lguest_write_gdt_entry(struct desc_struct *dt,
+ int entrynum, u32 low, u32 high)
+{
+ write_dt_entry(dt, entrynum, low, high);
+ hcall(LHCALL_LOAD_GDT, __pa(dt), GDT_ENTRIES, 0);
+}
+
+/* OK, I lied. There are three "thread local storage" GDT entries which change
+ * on every context switch (these three entries are how glibc implements
+ * __thread variables). So we have a hypercall specifically for this case. */
+static void lguest_load_tls(struct thread_struct *t, unsigned int cpu)
+{
+ /* There's one problem which normal hardware doesn't have: the Host
+ * can't handle us removing entries we're currently using. So we clear
+ * the GS register here: if it's needed it'll be reloaded anyway. */
+ loadsegment(gs, 0);
+ lazy_hcall(LHCALL_LOAD_TLS, __pa(&t->tls_array), cpu, 0);
+}
+
+/*G:038 That's enough excitement for now, back to ploughing through each of
+ * the different pv_ops structures (we're about 1/3 of the way through).
+ *
+ * This is the Local Descriptor Table, another weird Intel thingy. Linux only
+ * uses this for some strange applications like Wine. We don't do anything
+ * here, so they'll get an informative and friendly Segmentation Fault. */
+static void lguest_set_ldt(const void *addr, unsigned entries)
+{
+}
+
+/* This loads a GDT entry into the "Task Register": that entry points to a
+ * structure called the Task State Segment. Some comments scattered though the
+ * kernel code indicate that this used for task switching in ages past, along
+ * with blood sacrifice and astrology.
+ *
+ * Now there's nothing interesting in here that we don't get told elsewhere.
+ * But the native version uses the "ltr" instruction, which makes the Host
+ * complain to the Guest about a Segmentation Fault and it'll oops. So we
+ * override the native version with a do-nothing version. */
+static void lguest_load_tr_desc(void)
+{
+}
+
+/* The "cpuid" instruction is a way of querying both the CPU identity
+ * (manufacturer, model, etc) and its features. It was introduced before the
+ * Pentium in 1993 and keeps getting extended by both Intel and AMD. As you
+ * might imagine, after a decade and a half this treatment, it is now a giant
+ * ball of hair. Its entry in the current Intel manual runs to 28 pages.
+ *
+ * This instruction even it has its own Wikipedia entry. The Wikipedia entry
+ * has been translated into 4 languages. I am not making this up!
+ *
+ * We could get funky here and identify ourselves as "GenuineLguest", but
+ * instead we just use the real "cpuid" instruction. Then I pretty much turned
+ * off feature bits until the Guest booted. (Don't say that: you'll damage
+ * lguest sales!) Shut up, inner voice! (Hey, just pointing out that this is
+ * hardly future proof.) Noone's listening! They don't like you anyway,
+ * parenthetic weirdo!
+ *
+ * Replacing the cpuid so we can turn features off is great for the kernel, but
+ * anyone (including userspace) can just use the raw "cpuid" instruction and
+ * the Host won't even notice since it isn't privileged. So we try not to get
+ * too worked up about it. */
+static void lguest_cpuid(unsigned int *eax, unsigned int *ebx,
+ unsigned int *ecx, unsigned int *edx)
+{
+ int function = *eax;
+
+ native_cpuid(eax, ebx, ecx, edx);
+ switch (function) {
+ case 1: /* Basic feature request. */
+ /* We only allow kernel to see SSE3, CMPXCHG16B and SSSE3 */
+ *ecx &= 0x00002201;
+ /* SSE, SSE2, FXSR, MMX, CMOV, CMPXCHG8B, FPU. */
+ *edx &= 0x07808101;
+ /* The Host can do a nice optimization if it knows that the
+ * kernel mappings (addresses above 0xC0000000 or whatever
+ * PAGE_OFFSET is set to) haven't changed. But Linux calls
+ * flush_tlb_user() for both user and kernel mappings unless
+ * the Page Global Enable (PGE) feature bit is set. */
+ *edx |= 0x00002000;
+ break;
+ case 0x80000000:
+ /* Futureproof this a little: if they ask how much extended
+ * processor information there is, limit it to known fields. */
+ if (*eax > 0x80000008)
+ *eax = 0x80000008;
+ break;
+ }
+}
+
+/* Intel has four control registers, imaginatively named cr0, cr2, cr3 and cr4.
+ * I assume there's a cr1, but it hasn't bothered us yet, so we'll not bother
+ * it. The Host needs to know when the Guest wants to change them, so we have
+ * a whole series of functions like read_cr0() and write_cr0().
+ *
+ * We start with CR0. CR0 allows you to turn on and off all kinds of basic
+ * features, but Linux only really cares about one: the horrifically-named Task
+ * Switched (TS) bit at bit 3 (ie. 8)
+ *
+ * What does the TS bit do? Well, it causes the CPU to trap (interrupt 7) if
+ * the floating point unit is used. Which allows us to restore FPU state
+ * lazily after a task switch, and Linux uses that gratefully, but wouldn't a
+ * name like "FPUTRAP bit" be a little less cryptic?
+ *
+ * We store cr0 (and cr3) locally, because the Host never changes it. The
+ * Guest sometimes wants to read it and we'd prefer not to bother the Host
+ * unnecessarily. */
+static unsigned long current_cr0, current_cr3;
+static void lguest_write_cr0(unsigned long val)
+{
+ /* 8 == TS bit. */
+ lazy_hcall(LHCALL_TS, val & 8, 0, 0);
+ current_cr0 = val;
+}
+
+static unsigned long lguest_read_cr0(void)
+{
+ return current_cr0;
+}
+
+/* Intel provided a special instruction to clear the TS bit for people too cool
+ * to use write_cr0() to do it. This "clts" instruction is faster, because all
+ * the vowels have been optimized out. */
+static void lguest_clts(void)
+{
+ lazy_hcall(LHCALL_TS, 0, 0, 0);
+ current_cr0 &= ~8U;
+}
+
+/* CR2 is the virtual address of the last page fault, which the Guest only ever
+ * reads. The Host kindly writes this into our "struct lguest_data", so we
+ * just read it out of there. */
+static unsigned long lguest_read_cr2(void)
+{
+ return lguest_data.cr2;
+}
+
+/* CR3 is the current toplevel pagetable page: the principle is the same as
+ * cr0. Keep a local copy, and tell the Host when it changes. */
+static void lguest_write_cr3(unsigned long cr3)
+{
+ lazy_hcall(LHCALL_NEW_PGTABLE, cr3, 0, 0);
+ current_cr3 = cr3;
+}
+
+static unsigned long lguest_read_cr3(void)
+{
+ return current_cr3;
+}
+
+/* CR4 is used to enable and disable PGE, but we don't care. */
+static unsigned long lguest_read_cr4(void)
+{
+ return 0;
+}
+
+static void lguest_write_cr4(unsigned long val)
+{
+}
+
+/*
+ * Page Table Handling.
+ *
+ * Now would be a good time to take a rest and grab a coffee or similarly
+ * relaxing stimulant. The easy parts are behind us, and the trek gradually
+ * winds uphill from here.
+ *
+ * Quick refresher: memory is divided into "pages" of 4096 bytes each. The CPU
+ * maps virtual addresses to physical addresses using "page tables". We could
+ * use one huge index of 1 million entries: each address is 4 bytes, so that's
+ * 1024 pages just to hold the page tables. But since most virtual addresses
+ * are unused, we use a two level index which saves space. The CR3 register
+ * contains the physical address of the top level "page directory" page, which
+ * contains physical addresses of up to 1024 second-level pages. Each of these
+ * second level pages contains up to 1024 physical addresses of actual pages,
+ * or Page Table Entries (PTEs).
+ *
+ * Here's a diagram, where arrows indicate physical addresses:
+ *
+ * CR3 ---> +---------+
+ * | --------->+---------+
+ * | | | PADDR1 |
+ * Top-level | | PADDR2 |
+ * (PMD) page | | |
+ * | | Lower-level |
+ * | | (PTE) page |
+ * | | | |
+ * .... ....
+ *
+ * So to convert a virtual address to a physical address, we look up the top
+ * level, which points us to the second level, which gives us the physical
+ * address of that page. If the top level entry was not present, or the second
+ * level entry was not present, then the virtual address is invalid (we
+ * say "the page was not mapped").
+ *
+ * Put another way, a 32-bit virtual address is divided up like so:
+ *
+ * 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
+ * |<---- 10 bits ---->|<---- 10 bits ---->|<------ 12 bits ------>|
+ * Index into top Index into second Offset within page
+ * page directory page pagetable page
+ *
+ * The kernel spends a lot of time changing both the top-level page directory
+ * and lower-level pagetable pages. The Guest doesn't know physical addresses,
+ * so while it maintains these page tables exactly like normal, it also needs
+ * to keep the Host informed whenever it makes a change: the Host will create
+ * the real page tables based on the Guests'.
+ */
+
+/* The Guest calls this to set a second-level entry (pte), ie. to map a page
+ * into a process' address space. We set the entry then tell the Host the
+ * toplevel and address this corresponds to. The Guest uses one pagetable per
+ * process, so we need to tell the Host which one we're changing (mm->pgd). */
+static void lguest_set_pte_at(struct mm_struct *mm, unsigned long addr,
+ pte_t *ptep, pte_t pteval)
+{
+ *ptep = pteval;
+ lazy_hcall(LHCALL_SET_PTE, __pa(mm->pgd), addr, pteval.pte_low);
+}
+
+/* The Guest calls this to set a top-level entry. Again, we set the entry then
+ * tell the Host which top-level page we changed, and the index of the entry we
+ * changed. */
+static void lguest_set_pmd(pmd_t *pmdp, pmd_t pmdval)
+{
+ *pmdp = pmdval;
+ lazy_hcall(LHCALL_SET_PMD, __pa(pmdp)&PAGE_MASK,
+ (__pa(pmdp)&(PAGE_SIZE-1))/4, 0);
+}
+
+/* There are a couple of legacy places where the kernel sets a PTE, but we
+ * don't know the top level any more. This is useless for us, since we don't
+ * know which pagetable is changing or what address, so we just tell the Host
+ * to forget all of them. Fortunately, this is very rare.
+ *
+ * ... except in early boot when the kernel sets up the initial pagetables,
+ * which makes booting astonishingly slow. So we don't even tell the Host
+ * anything changed until we've done the first page table switch.
+ */
+static void lguest_set_pte(pte_t *ptep, pte_t pteval)
+{
+ *ptep = pteval;
+ /* Don't bother with hypercall before initial setup. */
+ if (current_cr3)
+ lazy_hcall(LHCALL_FLUSH_TLB, 1, 0, 0);
+}
+
+/* Unfortunately for Lguest, the pv_mmu_ops for page tables were based on
+ * native page table operations. On native hardware you can set a new page
+ * table entry whenever you want, but if you want to remove one you have to do
+ * a TLB flush (a TLB is a little cache of page table entries kept by the CPU).
+ *
+ * So the lguest_set_pte_at() and lguest_set_pmd() functions above are only
+ * called when a valid entry is written, not when it's removed (ie. marked not
+ * present). Instead, this is where we come when the Guest wants to remove a
+ * page table entry: we tell the Host to set that entry to 0 (ie. the present
+ * bit is zero). */
+static void lguest_flush_tlb_single(unsigned long addr)
+{
+ /* Simply set it to zero: if it was not, it will fault back in. */
+ lazy_hcall(LHCALL_SET_PTE, current_cr3, addr, 0);
+}
+
+/* This is what happens after the Guest has removed a large number of entries.
+ * This tells the Host that any of the page table entries for userspace might
+ * have changed, ie. virtual addresses below PAGE_OFFSET. */
+static void lguest_flush_tlb_user(void)
+{
+ lazy_hcall(LHCALL_FLUSH_TLB, 0, 0, 0);
+}
+
+/* This is called when the kernel page tables have changed. That's not very
+ * common (unless the Guest is using highmem, which makes the Guest extremely
+ * slow), so it's worth separating this from the user flushing above. */
+static void lguest_flush_tlb_kernel(void)
+{
+ lazy_hcall(LHCALL_FLUSH_TLB, 1, 0, 0);
+}
+
+/*
+ * The Unadvanced Programmable Interrupt Controller.
+ *
+ * This is an attempt to implement the simplest possible interrupt controller.
+ * I spent some time looking though routines like set_irq_chip_and_handler,
+ * set_irq_chip_and_handler_name, set_irq_chip_data and set_phasers_to_stun and
+ * I *think* this is as simple as it gets.
+ *
+ * We can tell the Host what interrupts we want blocked ready for using the
+ * lguest_data.interrupts bitmap, so disabling (aka "masking") them is as
+ * simple as setting a bit. We don't actually "ack" interrupts as such, we
+ * just mask and unmask them. I wonder if we should be cleverer?
+ */
+static void disable_lguest_irq(unsigned int irq)
+{
+ set_bit(irq, lguest_data.blocked_interrupts);
+}
+
+static void enable_lguest_irq(unsigned int irq)
+{
+ clear_bit(irq, lguest_data.blocked_interrupts);
+}
+
+/* This structure describes the lguest IRQ controller. */
+static struct irq_chip lguest_irq_controller = {
+ .name = "lguest",
+ .mask = disable_lguest_irq,
+ .mask_ack = disable_lguest_irq,
+ .unmask = enable_lguest_irq,
+};
+
+/* This sets up the Interrupt Descriptor Table (IDT) entry for each hardware
+ * interrupt (except 128, which is used for system calls), and then tells the
+ * Linux infrastructure that each interrupt is controlled by our level-based
+ * lguest interrupt controller. */
+static void __init lguest_init_IRQ(void)
+{
+ unsigned int i;
+
+ for (i = 0; i < LGUEST_IRQS; i++) {
+ int vector = FIRST_EXTERNAL_VECTOR + i;
+ if (vector != SYSCALL_VECTOR) {
+ set_intr_gate(vector, interrupt[i]);
+ set_irq_chip_and_handler(i, &lguest_irq_controller,
+ handle_level_irq);
+ }
+ }
+ /* This call is required to set up for 4k stacks, where we have
+ * separate stacks for hard and soft interrupts. */
+ irq_ctx_init(smp_processor_id());
+}
+
+/*
+ * Time.
+ *
+ * It would be far better for everyone if the Guest had its own clock, but
+ * until then the Host gives us the time on every interrupt.
+ */
+static unsigned long lguest_get_wallclock(void)
+{
+ return lguest_data.time.tv_sec;
+}
+
+static cycle_t lguest_clock_read(void)
+{
+ unsigned long sec, nsec;
+
+ /* If the Host tells the TSC speed, we can trust that. */
+ if (lguest_data.tsc_khz)
+ return native_read_tsc();
+
+ /* If we can't use the TSC, we read the time value written by the Host.
+ * Since it's in two parts (seconds and nanoseconds), we risk reading
+ * it just as it's changing from 99 & 0.999999999 to 100 and 0, and
+ * getting 99 and 0. As Linux tends to come apart under the stress of
+ * time travel, we must be careful: */
+ do {
+ /* First we read the seconds part. */
+ sec = lguest_data.time.tv_sec;
+ /* This read memory barrier tells the compiler and the CPU that
+ * this can't be reordered: we have to complete the above
+ * before going on. */
+ rmb();
+ /* Now we read the nanoseconds part. */
+ nsec = lguest_data.time.tv_nsec;
+ /* Make sure we've done that. */
+ rmb();
+ /* Now if the seconds part has changed, try again. */
+ } while (unlikely(lguest_data.time.tv_sec != sec));
+
+ /* Our non-TSC clock is in real nanoseconds. */
+ return sec*1000000000ULL + nsec;
+}
+
+/* This is what we tell the kernel is our clocksource. */
+static struct clocksource lguest_clock = {
+ .name = "lguest",
+ .rating = 400,
+ .read = lguest_clock_read,
+ .mask = CLOCKSOURCE_MASK(64),
+ .mult = 1 << 22,
+ .shift = 22,
+ .flags = CLOCK_SOURCE_IS_CONTINUOUS,
+};
+
+/* The "scheduler clock" is just our real clock, adjusted to start at zero */
+static unsigned long long lguest_sched_clock(void)
+{
+ return cyc2ns(&lguest_clock, lguest_clock_read() - clock_base);
+}
+
+/* We also need a "struct clock_event_device": Linux asks us to set it to go
+ * off some time in the future. Actually, James Morris figured all this out, I
+ * just applied the patch. */
+static int lguest_clockevent_set_next_event(unsigned long delta,
+ struct clock_event_device *evt)
+{
+ if (delta < LG_CLOCK_MIN_DELTA) {
+ if (printk_ratelimit())
+ printk(KERN_DEBUG "%s: small delta %lu ns\n",
+ __FUNCTION__, delta);
+ return -ETIME;
+ }
+ hcall(LHCALL_SET_CLOCKEVENT, delta, 0, 0);
+ return 0;
+}
+
+static void lguest_clockevent_set_mode(enum clock_event_mode mode,
+ struct clock_event_device *evt)
+{
+ switch (mode) {
+ case CLOCK_EVT_MODE_UNUSED:
+ case CLOCK_EVT_MODE_SHUTDOWN:
+ /* A 0 argument shuts the clock down. */
+ hcall(LHCALL_SET_CLOCKEVENT, 0, 0, 0);
+ break;
+ case CLOCK_EVT_MODE_ONESHOT:
+ /* This is what we expect. */
+ break;
+ case CLOCK_EVT_MODE_PERIODIC:
+ BUG();
+ case CLOCK_EVT_MODE_RESUME:
+ break;
+ }
+}
+
+/* This describes our primitive timer chip. */
+static struct clock_event_device lguest_clockevent = {
+ .name = "lguest",
+ .features = CLOCK_EVT_FEAT_ONESHOT,
+ .set_next_event = lguest_clockevent_set_next_event,
+ .set_mode = lguest_clockevent_set_mode,
+ .rating = INT_MAX,
+ .mult = 1,
+ .shift = 0,
+ .min_delta_ns = LG_CLOCK_MIN_DELTA,
+ .max_delta_ns = LG_CLOCK_MAX_DELTA,
+};
+
+/* This is the Guest timer interrupt handler (hardware interrupt 0). We just
+ * call the clockevent infrastructure and it does whatever needs doing. */
+static void lguest_time_irq(unsigned int irq, struct irq_desc *desc)
+{
+ unsigned long flags;
+
+ /* Don't interrupt us while this is running. */
+ local_irq_save(flags);
+ lguest_clockevent.event_handler(&lguest_clockevent);
+ local_irq_restore(flags);
+}
+
+/* At some point in the boot process, we get asked to set up our timing
+ * infrastructure. The kernel doesn't expect timer interrupts before this, but
+ * we cleverly initialized the "blocked_interrupts" field of "struct
+ * lguest_data" so that timer interrupts were blocked until now. */
+static void lguest_time_init(void)
+{
+ /* Set up the timer interrupt (0) to go to our simple timer routine */
+ set_irq_handler(0, lguest_time_irq);
+
+ /* Our clock structure look like arch/i386/kernel/tsc.c if we can use
+ * the TSC, otherwise it's a dumb nanosecond-resolution clock. Either
+ * way, the "rating" is initialized so high that it's always chosen
+ * over any other clocksource. */
+ if (lguest_data.tsc_khz)
+ lguest_clock.mult = clocksource_khz2mult(lguest_data.tsc_khz,
+ lguest_clock.shift);
+ clock_base = lguest_clock_read();
+ clocksource_register(&lguest_clock);
+
+ /* Now we've set up our clock, we can use it as the scheduler clock */
+ pv_time_ops.sched_clock = lguest_sched_clock;
+
+ /* We can't set cpumask in the initializer: damn C limitations! Set it
+ * here and register our timer device. */
+ lguest_clockevent.cpumask = cpumask_of_cpu(0);
+ clockevents_register_device(&lguest_clockevent);
+
+ /* Finally, we unblock the timer interrupt. */
+ enable_lguest_irq(0);
+}
+
+/*
+ * Miscellaneous bits and pieces.
+ *
+ * Here is an oddball collection of functions which the Guest needs for things
+ * to work. They're pretty simple.
+ */
+
+/* The Guest needs to tell the host what stack it expects traps to use. For
+ * native hardware, this is part of the Task State Segment mentioned above in
+ * lguest_load_tr_desc(), but to help hypervisors there's this special call.
+ *
+ * We tell the Host the segment we want to use (__KERNEL_DS is the kernel data
+ * segment), the privilege level (we're privilege level 1, the Host is 0 and
+ * will not tolerate us trying to use that), the stack pointer, and the number
+ * of pages in the stack. */
+static void lguest_load_esp0(struct tss_struct *tss,
+ struct thread_struct *thread)
+{
+ lazy_hcall(LHCALL_SET_STACK, __KERNEL_DS|0x1, thread->esp0,
+ THREAD_SIZE/PAGE_SIZE);
+}
+
+/* Let's just say, I wouldn't do debugging under a Guest. */
+static void lguest_set_debugreg(int regno, unsigned long value)
+{
+ /* FIXME: Implement */
+}
+
+/* There are times when the kernel wants to make sure that no memory writes are
+ * caught in the cache (that they've all reached real hardware devices). This
+ * doesn't matter for the Guest which has virtual hardware.
+ *
+ * On the Pentium 4 and above, cpuid() indicates that the Cache Line Flush
+ * (clflush) instruction is available and the kernel uses that. Otherwise, it
+ * uses the older "Write Back and Invalidate Cache" (wbinvd) instruction.
+ * Unlike clflush, wbinvd can only be run at privilege level 0. So we can
+ * ignore clflush, but replace wbinvd.
+ */
+static void lguest_wbinvd(void)
+{
+}
+
+/* If the Guest expects to have an Advanced Programmable Interrupt Controller,
+ * we play dumb by ignoring writes and returning 0 for reads. So it's no
+ * longer Programmable nor Controlling anything, and I don't think 8 lines of
+ * code qualifies for Advanced. It will also never interrupt anything. It
+ * does, however, allow us to get through the Linux boot code. */
+#ifdef CONFIG_X86_LOCAL_APIC
+static void lguest_apic_write(unsigned long reg, unsigned long v)
+{
+}
+
+static unsigned long lguest_apic_read(unsigned long reg)
+{
+ return 0;
+}
+#endif
+
+/* STOP! Until an interrupt comes in. */
+static void lguest_safe_halt(void)
+{
+ hcall(LHCALL_HALT, 0, 0, 0);
+}
+
+/* Perhaps CRASH isn't the best name for this hypercall, but we use it to get a
+ * message out when we're crashing as well as elegant termination like powering
+ * off.
+ *
+ * Note that the Host always prefers that the Guest speak in physical addresses
+ * rather than virtual addresses, so we use __pa() here. */
+static void lguest_power_off(void)
+{
+ hcall(LHCALL_CRASH, __pa("Power down"), 0, 0);
+}
+
+/*
+ * Panicing.
+ *
+ * Don't. But if you did, this is what happens.
+ */
+static int lguest_panic(struct notifier_block *nb, unsigned long l, void *p)
+{
+ hcall(LHCALL_CRASH, __pa(p), 0, 0);
+ /* The hcall won't return, but to keep gcc happy, we're "done". */
+ return NOTIFY_DONE;
+}
+
+static struct notifier_block paniced = {
+ .notifier_call = lguest_panic
+};
+
+/* Setting up memory is fairly easy. */
+static __init char *lguest_memory_setup(void)
+{
+ /* We do this here and not earlier because lockcheck barfs if we do it
+ * before start_kernel() */
+ atomic_notifier_chain_register(&panic_notifier_list, &paniced);
+
+ /* The Linux bootloader header contains an "e820" memory map: the
+ * Launcher populated the first entry with our memory limit. */
+ add_memory_region(boot_params.e820_map[0].addr,
+ boot_params.e820_map[0].size,
+ boot_params.e820_map[0].type);
+
+ /* This string is for the boot messages. */
+ return "LGUEST";
+}
+
+/*G:050
+ * Patching (Powerfully Placating Performance Pedants)
+ *
+ * We have already seen that pv_ops structures let us replace simple
+ * native instructions with calls to the appropriate back end all throughout
+ * the kernel. This allows the same kernel to run as a Guest and as a native
+ * kernel, but it's slow because of all the indirect branches.
+ *
+ * Remember that David Wheeler quote about "Any problem in computer science can
+ * be solved with another layer of indirection"? The rest of that quote is
+ * "... But that usually will create another problem." This is the first of
+ * those problems.
+ *
+ * Our current solution is to allow the paravirt back end to optionally patch
+ * over the indirect calls to replace them with something more efficient. We
+ * patch the four most commonly called functions: disable interrupts, enable
+ * interrupts, restore interrupts and save interrupts. We usually have 10
+ * bytes to patch into: the Guest versions of these operations are small enough
+ * that we can fit comfortably.
+ *
+ * First we need assembly templates of each of the patchable Guest operations,
+ * and these are in lguest_asm.S. */
+
+/*G:060 We construct a table from the assembler templates: */
+static const struct lguest_insns
+{
+ const char *start, *end;
+} lguest_insns[] = {
+ [PARAVIRT_PATCH(pv_irq_ops.irq_disable)] = { lgstart_cli, lgend_cli },
+ [PARAVIRT_PATCH(pv_irq_ops.irq_enable)] = { lgstart_sti, lgend_sti },
+ [PARAVIRT_PATCH(pv_irq_ops.restore_fl)] = { lgstart_popf, lgend_popf },
+ [PARAVIRT_PATCH(pv_irq_ops.save_fl)] = { lgstart_pushf, lgend_pushf },
+};
+
+/* Now our patch routine is fairly simple (based on the native one in
+ * paravirt.c). If we have a replacement, we copy it in and return how much of
+ * the available space we used. */
+static unsigned lguest_patch(u8 type, u16 clobber, void *ibuf,
+ unsigned long addr, unsigned len)
+{
+ unsigned int insn_len;
+
+ /* Don't do anything special if we don't have a replacement */
+ if (type >= ARRAY_SIZE(lguest_insns) || !lguest_insns[type].start)
+ return paravirt_patch_default(type, clobber, ibuf, addr, len);
+
+ insn_len = lguest_insns[type].end - lguest_insns[type].start;
+
+ /* Similarly if we can't fit replacement (shouldn't happen, but let's
+ * be thorough). */
+ if (len < insn_len)
+ return paravirt_patch_default(type, clobber, ibuf, addr, len);
+
+ /* Copy in our instructions. */
+ memcpy(ibuf, lguest_insns[type].start, insn_len);
+ return insn_len;
+}
+
+/*G:030 Once we get to lguest_init(), we know we're a Guest. The pv_ops
+ * structures in the kernel provide points for (almost) every routine we have
+ * to override to avoid privileged instructions. */
+__init void lguest_init(void *boot)
+{
+ /* Copy boot parameters first: the Launcher put the physical location
+ * in %esi, and head.S converted that to a virtual address and handed
+ * it to us. We use "__memcpy" because "memcpy" sometimes tries to do
+ * tricky things to go faster, and we're not ready for that. */
+ __memcpy(&boot_params, boot, PARAM_SIZE);
+ /* The boot parameters also tell us where the command-line is: save
+ * that, too. */
+ __memcpy(boot_command_line, __va(boot_params.hdr.cmd_line_ptr),
+ COMMAND_LINE_SIZE);
+
+ /* We're under lguest, paravirt is enabled, and we're running at
+ * privilege level 1, not 0 as normal. */
+ pv_info.name = "lguest";
+ pv_info.paravirt_enabled = 1;
+ pv_info.kernel_rpl = 1;
+
+ /* We set up all the lguest overrides for sensitive operations. These
+ * are detailed with the operations themselves. */
+
+ /* interrupt-related operations */
+ pv_irq_ops.init_IRQ = lguest_init_IRQ;
+ pv_irq_ops.save_fl = save_fl;
+ pv_irq_ops.restore_fl = restore_fl;
+ pv_irq_ops.irq_disable = irq_disable;
+ pv_irq_ops.irq_enable = irq_enable;
+ pv_irq_ops.safe_halt = lguest_safe_halt;
+
+ /* init-time operations */
+ pv_init_ops.memory_setup = lguest_memory_setup;
+ pv_init_ops.patch = lguest_patch;
+
+ /* Intercepts of various cpu instructions */
+ pv_cpu_ops.load_gdt = lguest_load_gdt;
+ pv_cpu_ops.cpuid = lguest_cpuid;
+ pv_cpu_ops.load_idt = lguest_load_idt;
+ pv_cpu_ops.iret = lguest_iret;
+ pv_cpu_ops.load_esp0 = lguest_load_esp0;
+ pv_cpu_ops.load_tr_desc = lguest_load_tr_desc;
+ pv_cpu_ops.set_ldt = lguest_set_ldt;
+ pv_cpu_ops.load_tls = lguest_load_tls;
+ pv_cpu_ops.set_debugreg = lguest_set_debugreg;
+ pv_cpu_ops.clts = lguest_clts;
+ pv_cpu_ops.read_cr0 = lguest_read_cr0;
+ pv_cpu_ops.write_cr0 = lguest_write_cr0;
+ pv_cpu_ops.read_cr4 = lguest_read_cr4;
+ pv_cpu_ops.write_cr4 = lguest_write_cr4;
+ pv_cpu_ops.write_gdt_entry = lguest_write_gdt_entry;
+ pv_cpu_ops.write_idt_entry = lguest_write_idt_entry;
+ pv_cpu_ops.wbinvd = lguest_wbinvd;
+ pv_cpu_ops.lazy_mode.enter = paravirt_enter_lazy_cpu;
+ pv_cpu_ops.lazy_mode.leave = lguest_leave_lazy_mode;
+
+ /* pagetable management */
+ pv_mmu_ops.write_cr3 = lguest_write_cr3;
+ pv_mmu_ops.flush_tlb_user = lguest_flush_tlb_user;
+ pv_mmu_ops.flush_tlb_single = lguest_flush_tlb_single;
+ pv_mmu_ops.flush_tlb_kernel = lguest_flush_tlb_kernel;
+ pv_mmu_ops.set_pte = lguest_set_pte;
+ pv_mmu_ops.set_pte_at = lguest_set_pte_at;
+ pv_mmu_ops.set_pmd = lguest_set_pmd;
+ pv_mmu_ops.read_cr2 = lguest_read_cr2;
+ pv_mmu_ops.read_cr3 = lguest_read_cr3;
+ pv_mmu_ops.lazy_mode.enter = paravirt_enter_lazy_mmu;
+ pv_mmu_ops.lazy_mode.leave = lguest_leave_lazy_mode;
+
+#ifdef CONFIG_X86_LOCAL_APIC
+ /* apic read/write intercepts */
+ pv_apic_ops.apic_write = lguest_apic_write;
+ pv_apic_ops.apic_write_atomic = lguest_apic_write;
+ pv_apic_ops.apic_read = lguest_apic_read;
+#endif
+
+ /* time operations */
+ pv_time_ops.get_wallclock = lguest_get_wallclock;
+ pv_time_ops.time_init = lguest_time_init;
+
+ /* Now is a good time to look at the implementations of these functions
+ * before returning to the rest of lguest_init(). */
+
+ /*G:070 Now we've seen all the paravirt_ops, we return to
+ * lguest_init() where the rest of the fairly chaotic boot setup
+ * occurs.
+ *
+ * The Host expects our first hypercall to tell it where our "struct
+ * lguest_data" is, so we do that first. */
+ hcall(LHCALL_LGUEST_INIT, __pa(&lguest_data), 0, 0);
+
+ /* The native boot code sets up initial page tables immediately after
+ * the kernel itself, and sets init_pg_tables_end so they're not
+ * clobbered. The Launcher places our initial pagetables somewhere at
+ * the top of our physical memory, so we don't need extra space: set
+ * init_pg_tables_end to the end of the kernel. */
+ init_pg_tables_end = __pa(pg0);
+
+ /* Load the %fs segment register (the per-cpu segment register) with
+ * the normal data segment to get through booting. */
+ asm volatile ("mov %0, %%fs" : : "r" (__KERNEL_DS) : "memory");
+
+ /* Clear the part of the kernel data which is expected to be zero.
+ * Normally it will be anyway, but if we're loading from a bzImage with
+ * CONFIG_RELOCATALE=y, the relocations will be sitting here. */
+ memset(__bss_start, 0, __bss_stop - __bss_start);
+
+ /* The Host uses the top of the Guest's virtual address space for the
+ * Host<->Guest Switcher, and it tells us how much it needs in
+ * lguest_data.reserve_mem, set up on the LGUEST_INIT hypercall. */
+ reserve_top_address(lguest_data.reserve_mem);
+
+ /* If we don't initialize the lock dependency checker now, it crashes
+ * paravirt_disable_iospace. */
+ lockdep_init();
+
+ /* The IDE code spends about 3 seconds probing for disks: if we reserve
+ * all the I/O ports up front it can't get them and so doesn't probe.
+ * Other device drivers are similar (but less severe). This cuts the
+ * kernel boot time on my machine from 4.1 seconds to 0.45 seconds. */
+ paravirt_disable_iospace();
+
+ /* This is messy CPU setup stuff which the native boot code does before
+ * start_kernel, so we have to do, too: */
+ cpu_detect(&new_cpu_data);
+ /* head.S usually sets up the first capability word, so do it here. */
+ new_cpu_data.x86_capability[0] = cpuid_edx(1);
+
+ /* Math is always hard! */
+ new_cpu_data.hard_math = 1;
+
+#ifdef CONFIG_X86_MCE
+ mce_disabled = 1;
+#endif
+#ifdef CONFIG_ACPI
+ acpi_disabled = 1;
+ acpi_ht = 0;
+#endif
+
+ /* We set the perferred console to "hvc". This is the "hypervisor
+ * virtual console" driver written by the PowerPC people, which we also
+ * adapted for lguest's use. */
+ add_preferred_console("hvc", 0, NULL);
+
+ /* Last of all, we set the power management poweroff hook to point to
+ * the Guest routine to power off. */
+ pm_power_off = lguest_power_off;
+
+ /* Now we're set up, call start_kernel() in init/main.c and we proceed
+ * to boot as normal. It never returns. */
+ start_kernel();
+}
+/*
+ * This marks the end of stage II of our journey, The Guest.
+ *
+ * It is now time for us to explore the nooks and crannies of the three Guest
+ * devices and complete our understanding of the Guest in "make Drivers".
+ */
--- /dev/null
+#include <linux/linkage.h>
+#include <linux/lguest.h>
+#include <asm/asm-offsets.h>
+#include <asm/thread_info.h>
+#include <asm/processor-flags.h>
+
+/*G:020 This is where we begin: we have a magic signature which the launcher
+ * looks for. The plan is that the Linux boot protocol will be extended with a
+ * "platform type" field which will guide us here from the normal entry point,
+ * but for the moment this suffices. The normal boot code uses %esi for the
+ * boot header, so we do too. We convert it to a virtual address by adding
+ * PAGE_OFFSET, and hand it to lguest_init() as its argument (ie. %eax).
+ *
+ * The .section line puts this code in .init.text so it will be discarded after
+ * boot. */
+.section .init.text, "ax", @progbits
+.ascii "GenuineLguest"
+ /* Set up initial stack. */
+ movl $(init_thread_union+THREAD_SIZE),%esp
+ movl %esi, %eax
+ addl $__PAGE_OFFSET, %eax
+ jmp lguest_init
+
+/*G:055 We create a macro which puts the assembler code between lgstart_ and
+ * lgend_ markers. These templates are put in the .text section: they can't be
+ * discarded after boot as we may need to patch modules, too. */
+.text
+#define LGUEST_PATCH(name, insns...) \
+ lgstart_##name: insns; lgend_##name:; \
+ .globl lgstart_##name; .globl lgend_##name
+
+LGUEST_PATCH(cli, movl $0, lguest_data+LGUEST_DATA_irq_enabled)
+LGUEST_PATCH(sti, movl $X86_EFLAGS_IF, lguest_data+LGUEST_DATA_irq_enabled)
+LGUEST_PATCH(popf, movl %eax, lguest_data+LGUEST_DATA_irq_enabled)
+LGUEST_PATCH(pushf, movl lguest_data+LGUEST_DATA_irq_enabled, %eax)
+/*:*/
+
+/* These demark the EIP range where host should never deliver interrupts. */
+.global lguest_noirq_start
+.global lguest_noirq_end
+
+/*M:004 When the Host reflects a trap or injects an interrupt into the Guest,
+ * it sets the eflags interrupt bit on the stack based on
+ * lguest_data.irq_enabled, so the Guest iret logic does the right thing when
+ * restoring it. However, when the Host sets the Guest up for direct traps,
+ * such as system calls, the processor is the one to push eflags onto the
+ * stack, and the interrupt bit will be 1 (in reality, interrupts are always
+ * enabled in the Guest).
+ *
+ * This turns out to be harmless: the only trap which should happen under Linux
+ * with interrupts disabled is Page Fault (due to our lazy mapping of vmalloc
+ * regions), which has to be reflected through the Host anyway. If another
+ * trap *does* go off when interrupts are disabled, the Guest will panic, and
+ * we'll never get to this iret! :*/
+
+/*G:045 There is one final paravirt_op that the Guest implements, and glancing
+ * at it you can see why I left it to last. It's *cool*! It's in *assembler*!
+ *
+ * The "iret" instruction is used to return from an interrupt or trap. The
+ * stack looks like this:
+ * old address
+ * old code segment & privilege level
+ * old processor flags ("eflags")
+ *
+ * The "iret" instruction pops those values off the stack and restores them all
+ * at once. The only problem is that eflags includes the Interrupt Flag which
+ * the Guest can't change: the CPU will simply ignore it when we do an "iret".
+ * So we have to copy eflags from the stack to lguest_data.irq_enabled before
+ * we do the "iret".
+ *
+ * There are two problems with this: firstly, we need to use a register to do
+ * the copy and secondly, the whole thing needs to be atomic. The first
+ * problem is easy to solve: push %eax on the stack so we can use it, and then
+ * restore it at the end just before the real "iret".
+ *
+ * The second is harder: copying eflags to lguest_data.irq_enabled will turn
+ * interrupts on before we're finished, so we could be interrupted before we
+ * return to userspace or wherever. Our solution to this is to surround the
+ * code with lguest_noirq_start: and lguest_noirq_end: labels. We tell the
+ * Host that it is *never* to interrupt us there, even if interrupts seem to be
+ * enabled. */
+ENTRY(lguest_iret)
+ pushl %eax
+ movl 12(%esp), %eax
+lguest_noirq_start:
+ /* Note the %ss: segment prefix here. Normal data accesses use the
+ * "ds" segment, but that will have already been restored for whatever
+ * we're returning to (such as userspace): we can't trust it. The %ss:
+ * prefix makes sure we use the stack segment, which is still valid. */
+ movl %eax,%ss:lguest_data+LGUEST_DATA_irq_enabled
+ popl %eax
+ iret
+lguest_noirq_end:
-# Guest requires the paravirt_ops replacement and the bus driver.
-obj-$(CONFIG_LGUEST_GUEST) += lguest.o lguest_asm.o lguest_bus.o
+# Guest requires the bus driver.
+obj-$(CONFIG_LGUEST_GUEST) += lguest_bus.o
# Host requires the other files, which can be a module.
obj-$(CONFIG_LGUEST) += lg.o
+++ /dev/null
-/*P:010
- * A hypervisor allows multiple Operating Systems to run on a single machine.
- * To quote David Wheeler: "Any problem in computer science can be solved with
- * another layer of indirection."
- *
- * We keep things simple in two ways. First, we start with a normal Linux
- * kernel and insert a module (lg.ko) which allows us to run other Linux
- * kernels the same way we'd run processes. We call the first kernel the Host,
- * and the others the Guests. The program which sets up and configures Guests
- * (such as the example in Documentation/lguest/lguest.c) is called the
- * Launcher.
- *
- * Secondly, we only run specially modified Guests, not normal kernels. When
- * you set CONFIG_LGUEST to 'y' or 'm', this automatically sets
- * CONFIG_LGUEST_GUEST=y, which compiles this file into the kernel so it knows
- * how to be a Guest. This means that you can use the same kernel you boot
- * normally (ie. as a Host) as a Guest.
- *
- * These Guests know that they cannot do privileged operations, such as disable
- * interrupts, and that they have to ask the Host to do such things explicitly.
- * This file consists of all the replacements for such low-level native
- * hardware operations: these special Guest versions call the Host.
- *
- * So how does the kernel know it's a Guest? The Guest starts at a special
- * entry point marked with a magic string, which sets up a few things then
- * calls here. We replace the native functions various "paravirt" structures
- * with our Guest versions, then boot like normal. :*/
-
-/*
- * Copyright (C) 2006, Rusty Russell <rusty@rustcorp.com.au> IBM Corporation.
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful, but
- * WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
- * NON INFRINGEMENT. See the GNU General Public License for more
- * details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
- */
-#include <linux/kernel.h>
-#include <linux/start_kernel.h>
-#include <linux/string.h>
-#include <linux/console.h>
-#include <linux/screen_info.h>
-#include <linux/irq.h>
-#include <linux/interrupt.h>
-#include <linux/clocksource.h>
-#include <linux/clockchips.h>
-#include <linux/lguest.h>
-#include <linux/lguest_launcher.h>
-#include <linux/lguest_bus.h>
-#include <asm/paravirt.h>
-#include <asm/param.h>
-#include <asm/page.h>
-#include <asm/pgtable.h>
-#include <asm/desc.h>
-#include <asm/setup.h>
-#include <asm/e820.h>
-#include <asm/mce.h>
-#include <asm/io.h>
-
-/*G:010 Welcome to the Guest!
- *
- * The Guest in our tale is a simple creature: identical to the Host but
- * behaving in simplified but equivalent ways. In particular, the Guest is the
- * same kernel as the Host (or at least, built from the same source code). :*/
-
-/* Declarations for definitions in lguest_guest.S */
-extern char lguest_noirq_start[], lguest_noirq_end[];
-extern const char lgstart_cli[], lgend_cli[];
-extern const char lgstart_sti[], lgend_sti[];
-extern const char lgstart_popf[], lgend_popf[];
-extern const char lgstart_pushf[], lgend_pushf[];
-extern const char lgstart_iret[], lgend_iret[];
-extern void lguest_iret(void);
-
-struct lguest_data lguest_data = {
- .hcall_status = { [0 ... LHCALL_RING_SIZE-1] = 0xFF },
- .noirq_start = (u32)lguest_noirq_start,
- .noirq_end = (u32)lguest_noirq_end,
- .blocked_interrupts = { 1 }, /* Block timer interrupts */
-};
-static cycle_t clock_base;
-
-/*G:035 Notice the lazy_hcall() above, rather than hcall(). This is our first
- * real optimization trick!
- *
- * When lazy_mode is set, it means we're allowed to defer all hypercalls and do
- * them as a batch when lazy_mode is eventually turned off. Because hypercalls
- * are reasonably expensive, batching them up makes sense. For example, a
- * large mmap might update dozens of page table entries: that code calls
- * paravirt_enter_lazy_mmu(), does the dozen updates, then calls
- * lguest_leave_lazy_mode().
- *
- * So, when we're in lazy mode, we call async_hypercall() to store the call for
- * future processing. When lazy mode is turned off we issue a hypercall to
- * flush the stored calls.
- */
-static void lguest_leave_lazy_mode(void)
-{
- paravirt_leave_lazy(paravirt_get_lazy_mode());
- hcall(LHCALL_FLUSH_ASYNC, 0, 0, 0);
-}
-
-static void lazy_hcall(unsigned long call,
- unsigned long arg1,
- unsigned long arg2,
- unsigned long arg3)
-{
- if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE)
- hcall(call, arg1, arg2, arg3);
- else
- async_hcall(call, arg1, arg2, arg3);
-}
-
-/* async_hcall() is pretty simple: I'm quite proud of it really. We have a
- * ring buffer of stored hypercalls which the Host will run though next time we
- * do a normal hypercall. Each entry in the ring has 4 slots for the hypercall
- * arguments, and a "hcall_status" word which is 0 if the call is ready to go,
- * and 255 once the Host has finished with it.
- *
- * If we come around to a slot which hasn't been finished, then the table is
- * full and we just make the hypercall directly. This has the nice side
- * effect of causing the Host to run all the stored calls in the ring buffer
- * which empties it for next time! */
-void async_hcall(unsigned long call,
- unsigned long arg1, unsigned long arg2, unsigned long arg3)
-{
- /* Note: This code assumes we're uniprocessor. */
- static unsigned int next_call;
- unsigned long flags;
-
- /* Disable interrupts if not already disabled: we don't want an
- * interrupt handler making a hypercall while we're already doing
- * one! */
- local_irq_save(flags);
- if (lguest_data.hcall_status[next_call] != 0xFF) {
- /* Table full, so do normal hcall which will flush table. */
- hcall(call, arg1, arg2, arg3);
- } else {
- lguest_data.hcalls[next_call].eax = call;
- lguest_data.hcalls[next_call].edx = arg1;
- lguest_data.hcalls[next_call].ebx = arg2;
- lguest_data.hcalls[next_call].ecx = arg3;
- /* Arguments must all be written before we mark it to go */
- wmb();
- lguest_data.hcall_status[next_call] = 0;
- if (++next_call == LHCALL_RING_SIZE)
- next_call = 0;
- }
- local_irq_restore(flags);
-}
-/*:*/
-
-/* Wrappers for the SEND_DMA and BIND_DMA hypercalls. This is mainly because
- * Jeff Garzik complained that __pa() should never appear in drivers, and this
- * helps remove most of them. But also, it wraps some ugliness. */
-void lguest_send_dma(unsigned long key, struct lguest_dma *dma)
-{
- /* The hcall might not write this if something goes wrong */
- dma->used_len = 0;
- hcall(LHCALL_SEND_DMA, key, __pa(dma), 0);
-}
-
-int lguest_bind_dma(unsigned long key, struct lguest_dma *dmas,
- unsigned int num, u8 irq)
-{
- /* This is the only hypercall which actually wants 5 arguments, and we
- * only support 4. Fortunately the interrupt number is always less
- * than 256, so we can pack it with the number of dmas in the final
- * argument. */
- if (!hcall(LHCALL_BIND_DMA, key, __pa(dmas), (num << 8) | irq))
- return -ENOMEM;
- return 0;
-}
-
-/* Unbinding is the same hypercall as binding, but with 0 num & irq. */
-void lguest_unbind_dma(unsigned long key, struct lguest_dma *dmas)
-{
- hcall(LHCALL_BIND_DMA, key, __pa(dmas), 0);
-}
-
-/* For guests, device memory can be used as normal memory, so we cast away the
- * __iomem to quieten sparse. */
-void *lguest_map(unsigned long phys_addr, unsigned long pages)
-{
- return (__force void *)ioremap(phys_addr, PAGE_SIZE*pages);
-}
-
-void lguest_unmap(void *addr)
-{
- iounmap((__force void __iomem *)addr);
-}
-
-/*G:033
- * Here are our first native-instruction replacements: four functions for
- * interrupt control.
- *
- * The simplest way of implementing these would be to have "turn interrupts
- * off" and "turn interrupts on" hypercalls. Unfortunately, this is too slow:
- * these are by far the most commonly called functions of those we override.
- *
- * So instead we keep an "irq_enabled" field inside our "struct lguest_data",
- * which the Guest can update with a single instruction. The Host knows to
- * check there when it wants to deliver an interrupt.
- */
-
-/* save_flags() is expected to return the processor state (ie. "eflags"). The
- * eflags word contains all kind of stuff, but in practice Linux only cares
- * about the interrupt flag. Our "save_flags()" just returns that. */
-static unsigned long save_fl(void)
-{
- return lguest_data.irq_enabled;
-}
-
-/* "restore_flags" just sets the flags back to the value given. */
-static void restore_fl(unsigned long flags)
-{
- lguest_data.irq_enabled = flags;
-}
-
-/* Interrupts go off... */
-static void irq_disable(void)
-{
- lguest_data.irq_enabled = 0;
-}
-
-/* Interrupts go on... */
-static void irq_enable(void)
-{
- lguest_data.irq_enabled = X86_EFLAGS_IF;
-}
-/*:*/
-/*M:003 Note that we don't check for outstanding interrupts when we re-enable
- * them (or when we unmask an interrupt). This seems to work for the moment,
- * since interrupts are rare and we'll just get the interrupt on the next timer
- * tick, but when we turn on CONFIG_NO_HZ, we should revisit this. One way
- * would be to put the "irq_enabled" field in a page by itself, and have the
- * Host write-protect it when an interrupt comes in when irqs are disabled.
- * There will then be a page fault as soon as interrupts are re-enabled. :*/
-
-/*G:034
- * The Interrupt Descriptor Table (IDT).
- *
- * The IDT tells the processor what to do when an interrupt comes in. Each
- * entry in the table is a 64-bit descriptor: this holds the privilege level,
- * address of the handler, and... well, who cares? The Guest just asks the
- * Host to make the change anyway, because the Host controls the real IDT.
- */
-static void lguest_write_idt_entry(struct desc_struct *dt,
- int entrynum, u32 low, u32 high)
-{
- /* Keep the local copy up to date. */
- write_dt_entry(dt, entrynum, low, high);
- /* Tell Host about this new entry. */
- hcall(LHCALL_LOAD_IDT_ENTRY, entrynum, low, high);
-}
-
-/* Changing to a different IDT is very rare: we keep the IDT up-to-date every
- * time it is written, so we can simply loop through all entries and tell the
- * Host about them. */
-static void lguest_load_idt(const struct Xgt_desc_struct *desc)
-{
- unsigned int i;
- struct desc_struct *idt = (void *)desc->address;
-
- for (i = 0; i < (desc->size+1)/8; i++)
- hcall(LHCALL_LOAD_IDT_ENTRY, i, idt[i].a, idt[i].b);
-}
-
-/*
- * The Global Descriptor Table.
- *
- * The Intel architecture defines another table, called the Global Descriptor
- * Table (GDT). You tell the CPU where it is (and its size) using the "lgdt"
- * instruction, and then several other instructions refer to entries in the
- * table. There are three entries which the Switcher needs, so the Host simply
- * controls the entire thing and the Guest asks it to make changes using the
- * LOAD_GDT hypercall.
- *
- * This is the opposite of the IDT code where we have a LOAD_IDT_ENTRY
- * hypercall and use that repeatedly to load a new IDT. I don't think it
- * really matters, but wouldn't it be nice if they were the same?
- */
-static void lguest_load_gdt(const struct Xgt_desc_struct *desc)
-{
- BUG_ON((desc->size+1)/8 != GDT_ENTRIES);
- hcall(LHCALL_LOAD_GDT, __pa(desc->address), GDT_ENTRIES, 0);
-}
-
-/* For a single GDT entry which changes, we do the lazy thing: alter our GDT,
- * then tell the Host to reload the entire thing. This operation is so rare
- * that this naive implementation is reasonable. */
-static void lguest_write_gdt_entry(struct desc_struct *dt,
- int entrynum, u32 low, u32 high)
-{
- write_dt_entry(dt, entrynum, low, high);
- hcall(LHCALL_LOAD_GDT, __pa(dt), GDT_ENTRIES, 0);
-}
-
-/* OK, I lied. There are three "thread local storage" GDT entries which change
- * on every context switch (these three entries are how glibc implements
- * __thread variables). So we have a hypercall specifically for this case. */
-static void lguest_load_tls(struct thread_struct *t, unsigned int cpu)
-{
- /* There's one problem which normal hardware doesn't have: the Host
- * can't handle us removing entries we're currently using. So we clear
- * the GS register here: if it's needed it'll be reloaded anyway. */
- loadsegment(gs, 0);
- lazy_hcall(LHCALL_LOAD_TLS, __pa(&t->tls_array), cpu, 0);
-}
-
-/*G:038 That's enough excitement for now, back to ploughing through each of
- * the different pv_ops structures (we're about 1/3 of the way through).
- *
- * This is the Local Descriptor Table, another weird Intel thingy. Linux only
- * uses this for some strange applications like Wine. We don't do anything
- * here, so they'll get an informative and friendly Segmentation Fault. */
-static void lguest_set_ldt(const void *addr, unsigned entries)
-{
-}
-
-/* This loads a GDT entry into the "Task Register": that entry points to a
- * structure called the Task State Segment. Some comments scattered though the
- * kernel code indicate that this used for task switching in ages past, along
- * with blood sacrifice and astrology.
- *
- * Now there's nothing interesting in here that we don't get told elsewhere.
- * But the native version uses the "ltr" instruction, which makes the Host
- * complain to the Guest about a Segmentation Fault and it'll oops. So we
- * override the native version with a do-nothing version. */
-static void lguest_load_tr_desc(void)
-{
-}
-
-/* The "cpuid" instruction is a way of querying both the CPU identity
- * (manufacturer, model, etc) and its features. It was introduced before the
- * Pentium in 1993 and keeps getting extended by both Intel and AMD. As you
- * might imagine, after a decade and a half this treatment, it is now a giant
- * ball of hair. Its entry in the current Intel manual runs to 28 pages.
- *
- * This instruction even it has its own Wikipedia entry. The Wikipedia entry
- * has been translated into 4 languages. I am not making this up!
- *
- * We could get funky here and identify ourselves as "GenuineLguest", but
- * instead we just use the real "cpuid" instruction. Then I pretty much turned
- * off feature bits until the Guest booted. (Don't say that: you'll damage
- * lguest sales!) Shut up, inner voice! (Hey, just pointing out that this is
- * hardly future proof.) Noone's listening! They don't like you anyway,
- * parenthetic weirdo!
- *
- * Replacing the cpuid so we can turn features off is great for the kernel, but
- * anyone (including userspace) can just use the raw "cpuid" instruction and
- * the Host won't even notice since it isn't privileged. So we try not to get
- * too worked up about it. */
-static void lguest_cpuid(unsigned int *eax, unsigned int *ebx,
- unsigned int *ecx, unsigned int *edx)
-{
- int function = *eax;
-
- native_cpuid(eax, ebx, ecx, edx);
- switch (function) {
- case 1: /* Basic feature request. */
- /* We only allow kernel to see SSE3, CMPXCHG16B and SSSE3 */
- *ecx &= 0x00002201;
- /* SSE, SSE2, FXSR, MMX, CMOV, CMPXCHG8B, FPU. */
- *edx &= 0x07808101;
- /* The Host can do a nice optimization if it knows that the
- * kernel mappings (addresses above 0xC0000000 or whatever
- * PAGE_OFFSET is set to) haven't changed. But Linux calls
- * flush_tlb_user() for both user and kernel mappings unless
- * the Page Global Enable (PGE) feature bit is set. */
- *edx |= 0x00002000;
- break;
- case 0x80000000:
- /* Futureproof this a little: if they ask how much extended
- * processor information there is, limit it to known fields. */
- if (*eax > 0x80000008)
- *eax = 0x80000008;
- break;
- }
-}
-
-/* Intel has four control registers, imaginatively named cr0, cr2, cr3 and cr4.
- * I assume there's a cr1, but it hasn't bothered us yet, so we'll not bother
- * it. The Host needs to know when the Guest wants to change them, so we have
- * a whole series of functions like read_cr0() and write_cr0().
- *
- * We start with CR0. CR0 allows you to turn on and off all kinds of basic
- * features, but Linux only really cares about one: the horrifically-named Task
- * Switched (TS) bit at bit 3 (ie. 8)
- *
- * What does the TS bit do? Well, it causes the CPU to trap (interrupt 7) if
- * the floating point unit is used. Which allows us to restore FPU state
- * lazily after a task switch, and Linux uses that gratefully, but wouldn't a
- * name like "FPUTRAP bit" be a little less cryptic?
- *
- * We store cr0 (and cr3) locally, because the Host never changes it. The
- * Guest sometimes wants to read it and we'd prefer not to bother the Host
- * unnecessarily. */
-static unsigned long current_cr0, current_cr3;
-static void lguest_write_cr0(unsigned long val)
-{
- /* 8 == TS bit. */
- lazy_hcall(LHCALL_TS, val & 8, 0, 0);
- current_cr0 = val;
-}
-
-static unsigned long lguest_read_cr0(void)
-{
- return current_cr0;
-}
-
-/* Intel provided a special instruction to clear the TS bit for people too cool
- * to use write_cr0() to do it. This "clts" instruction is faster, because all
- * the vowels have been optimized out. */
-static void lguest_clts(void)
-{
- lazy_hcall(LHCALL_TS, 0, 0, 0);
- current_cr0 &= ~8U;
-}
-
-/* CR2 is the virtual address of the last page fault, which the Guest only ever
- * reads. The Host kindly writes this into our "struct lguest_data", so we
- * just read it out of there. */
-static unsigned long lguest_read_cr2(void)
-{
- return lguest_data.cr2;
-}
-
-/* CR3 is the current toplevel pagetable page: the principle is the same as
- * cr0. Keep a local copy, and tell the Host when it changes. */
-static void lguest_write_cr3(unsigned long cr3)
-{
- lazy_hcall(LHCALL_NEW_PGTABLE, cr3, 0, 0);
- current_cr3 = cr3;
-}
-
-static unsigned long lguest_read_cr3(void)
-{
- return current_cr3;
-}
-
-/* CR4 is used to enable and disable PGE, but we don't care. */
-static unsigned long lguest_read_cr4(void)
-{
- return 0;
-}
-
-static void lguest_write_cr4(unsigned long val)
-{
-}
-
-/*
- * Page Table Handling.
- *
- * Now would be a good time to take a rest and grab a coffee or similarly
- * relaxing stimulant. The easy parts are behind us, and the trek gradually
- * winds uphill from here.
- *
- * Quick refresher: memory is divided into "pages" of 4096 bytes each. The CPU
- * maps virtual addresses to physical addresses using "page tables". We could
- * use one huge index of 1 million entries: each address is 4 bytes, so that's
- * 1024 pages just to hold the page tables. But since most virtual addresses
- * are unused, we use a two level index which saves space. The CR3 register
- * contains the physical address of the top level "page directory" page, which
- * contains physical addresses of up to 1024 second-level pages. Each of these
- * second level pages contains up to 1024 physical addresses of actual pages,
- * or Page Table Entries (PTEs).
- *
- * Here's a diagram, where arrows indicate physical addresses:
- *
- * CR3 ---> +---------+
- * | --------->+---------+
- * | | | PADDR1 |
- * Top-level | | PADDR2 |
- * (PMD) page | | |
- * | | Lower-level |
- * | | (PTE) page |
- * | | | |
- * .... ....
- *
- * So to convert a virtual address to a physical address, we look up the top
- * level, which points us to the second level, which gives us the physical
- * address of that page. If the top level entry was not present, or the second
- * level entry was not present, then the virtual address is invalid (we
- * say "the page was not mapped").
- *
- * Put another way, a 32-bit virtual address is divided up like so:
- *
- * 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
- * |<---- 10 bits ---->|<---- 10 bits ---->|<------ 12 bits ------>|
- * Index into top Index into second Offset within page
- * page directory page pagetable page
- *
- * The kernel spends a lot of time changing both the top-level page directory
- * and lower-level pagetable pages. The Guest doesn't know physical addresses,
- * so while it maintains these page tables exactly like normal, it also needs
- * to keep the Host informed whenever it makes a change: the Host will create
- * the real page tables based on the Guests'.
- */
-
-/* The Guest calls this to set a second-level entry (pte), ie. to map a page
- * into a process' address space. We set the entry then tell the Host the
- * toplevel and address this corresponds to. The Guest uses one pagetable per
- * process, so we need to tell the Host which one we're changing (mm->pgd). */
-static void lguest_set_pte_at(struct mm_struct *mm, unsigned long addr,
- pte_t *ptep, pte_t pteval)
-{
- *ptep = pteval;
- lazy_hcall(LHCALL_SET_PTE, __pa(mm->pgd), addr, pteval.pte_low);
-}
-
-/* The Guest calls this to set a top-level entry. Again, we set the entry then
- * tell the Host which top-level page we changed, and the index of the entry we
- * changed. */
-static void lguest_set_pmd(pmd_t *pmdp, pmd_t pmdval)
-{
- *pmdp = pmdval;
- lazy_hcall(LHCALL_SET_PMD, __pa(pmdp)&PAGE_MASK,
- (__pa(pmdp)&(PAGE_SIZE-1))/4, 0);
-}
-
-/* There are a couple of legacy places where the kernel sets a PTE, but we
- * don't know the top level any more. This is useless for us, since we don't
- * know which pagetable is changing or what address, so we just tell the Host
- * to forget all of them. Fortunately, this is very rare.
- *
- * ... except in early boot when the kernel sets up the initial pagetables,
- * which makes booting astonishingly slow. So we don't even tell the Host
- * anything changed until we've done the first page table switch.
- */
-static void lguest_set_pte(pte_t *ptep, pte_t pteval)
-{
- *ptep = pteval;
- /* Don't bother with hypercall before initial setup. */
- if (current_cr3)
- lazy_hcall(LHCALL_FLUSH_TLB, 1, 0, 0);
-}
-
-/* Unfortunately for Lguest, the pv_mmu_ops for page tables were based on
- * native page table operations. On native hardware you can set a new page
- * table entry whenever you want, but if you want to remove one you have to do
- * a TLB flush (a TLB is a little cache of page table entries kept by the CPU).
- *
- * So the lguest_set_pte_at() and lguest_set_pmd() functions above are only
- * called when a valid entry is written, not when it's removed (ie. marked not
- * present). Instead, this is where we come when the Guest wants to remove a
- * page table entry: we tell the Host to set that entry to 0 (ie. the present
- * bit is zero). */
-static void lguest_flush_tlb_single(unsigned long addr)
-{
- /* Simply set it to zero: if it was not, it will fault back in. */
- lazy_hcall(LHCALL_SET_PTE, current_cr3, addr, 0);
-}
-
-/* This is what happens after the Guest has removed a large number of entries.
- * This tells the Host that any of the page table entries for userspace might
- * have changed, ie. virtual addresses below PAGE_OFFSET. */
-static void lguest_flush_tlb_user(void)
-{
- lazy_hcall(LHCALL_FLUSH_TLB, 0, 0, 0);
-}
-
-/* This is called when the kernel page tables have changed. That's not very
- * common (unless the Guest is using highmem, which makes the Guest extremely
- * slow), so it's worth separating this from the user flushing above. */
-static void lguest_flush_tlb_kernel(void)
-{
- lazy_hcall(LHCALL_FLUSH_TLB, 1, 0, 0);
-}
-
-/*
- * The Unadvanced Programmable Interrupt Controller.
- *
- * This is an attempt to implement the simplest possible interrupt controller.
- * I spent some time looking though routines like set_irq_chip_and_handler,
- * set_irq_chip_and_handler_name, set_irq_chip_data and set_phasers_to_stun and
- * I *think* this is as simple as it gets.
- *
- * We can tell the Host what interrupts we want blocked ready for using the
- * lguest_data.interrupts bitmap, so disabling (aka "masking") them is as
- * simple as setting a bit. We don't actually "ack" interrupts as such, we
- * just mask and unmask them. I wonder if we should be cleverer?
- */
-static void disable_lguest_irq(unsigned int irq)
-{
- set_bit(irq, lguest_data.blocked_interrupts);
-}
-
-static void enable_lguest_irq(unsigned int irq)
-{
- clear_bit(irq, lguest_data.blocked_interrupts);
-}
-
-/* This structure describes the lguest IRQ controller. */
-static struct irq_chip lguest_irq_controller = {
- .name = "lguest",
- .mask = disable_lguest_irq,
- .mask_ack = disable_lguest_irq,
- .unmask = enable_lguest_irq,
-};
-
-/* This sets up the Interrupt Descriptor Table (IDT) entry for each hardware
- * interrupt (except 128, which is used for system calls), and then tells the
- * Linux infrastructure that each interrupt is controlled by our level-based
- * lguest interrupt controller. */
-static void __init lguest_init_IRQ(void)
-{
- unsigned int i;
-
- for (i = 0; i < LGUEST_IRQS; i++) {
- int vector = FIRST_EXTERNAL_VECTOR + i;
- if (vector != SYSCALL_VECTOR) {
- set_intr_gate(vector, interrupt[i]);
- set_irq_chip_and_handler(i, &lguest_irq_controller,
- handle_level_irq);
- }
- }
- /* This call is required to set up for 4k stacks, where we have
- * separate stacks for hard and soft interrupts. */
- irq_ctx_init(smp_processor_id());
-}
-
-/*
- * Time.
- *
- * It would be far better for everyone if the Guest had its own clock, but
- * until then the Host gives us the time on every interrupt.
- */
-static unsigned long lguest_get_wallclock(void)
-{
- return lguest_data.time.tv_sec;
-}
-
-static cycle_t lguest_clock_read(void)
-{
- unsigned long sec, nsec;
-
- /* If the Host tells the TSC speed, we can trust that. */
- if (lguest_data.tsc_khz)
- return native_read_tsc();
-
- /* If we can't use the TSC, we read the time value written by the Host.
- * Since it's in two parts (seconds and nanoseconds), we risk reading
- * it just as it's changing from 99 & 0.999999999 to 100 and 0, and
- * getting 99 and 0. As Linux tends to come apart under the stress of
- * time travel, we must be careful: */
- do {
- /* First we read the seconds part. */
- sec = lguest_data.time.tv_sec;
- /* This read memory barrier tells the compiler and the CPU that
- * this can't be reordered: we have to complete the above
- * before going on. */
- rmb();
- /* Now we read the nanoseconds part. */
- nsec = lguest_data.time.tv_nsec;
- /* Make sure we've done that. */
- rmb();
- /* Now if the seconds part has changed, try again. */
- } while (unlikely(lguest_data.time.tv_sec != sec));
-
- /* Our non-TSC clock is in real nanoseconds. */
- return sec*1000000000ULL + nsec;
-}
-
-/* This is what we tell the kernel is our clocksource. */
-static struct clocksource lguest_clock = {
- .name = "lguest",
- .rating = 400,
- .read = lguest_clock_read,
- .mask = CLOCKSOURCE_MASK(64),
- .mult = 1 << 22,
- .shift = 22,
- .flags = CLOCK_SOURCE_IS_CONTINUOUS,
-};
-
-/* The "scheduler clock" is just our real clock, adjusted to start at zero */
-static unsigned long long lguest_sched_clock(void)
-{
- return cyc2ns(&lguest_clock, lguest_clock_read() - clock_base);
-}
-
-/* We also need a "struct clock_event_device": Linux asks us to set it to go
- * off some time in the future. Actually, James Morris figured all this out, I
- * just applied the patch. */
-static int lguest_clockevent_set_next_event(unsigned long delta,
- struct clock_event_device *evt)
-{
- if (delta < LG_CLOCK_MIN_DELTA) {
- if (printk_ratelimit())
- printk(KERN_DEBUG "%s: small delta %lu ns\n",
- __FUNCTION__, delta);
- return -ETIME;
- }
- hcall(LHCALL_SET_CLOCKEVENT, delta, 0, 0);
- return 0;
-}
-
-static void lguest_clockevent_set_mode(enum clock_event_mode mode,
- struct clock_event_device *evt)
-{
- switch (mode) {
- case CLOCK_EVT_MODE_UNUSED:
- case CLOCK_EVT_MODE_SHUTDOWN:
- /* A 0 argument shuts the clock down. */
- hcall(LHCALL_SET_CLOCKEVENT, 0, 0, 0);
- break;
- case CLOCK_EVT_MODE_ONESHOT:
- /* This is what we expect. */
- break;
- case CLOCK_EVT_MODE_PERIODIC:
- BUG();
- case CLOCK_EVT_MODE_RESUME:
- break;
- }
-}
-
-/* This describes our primitive timer chip. */
-static struct clock_event_device lguest_clockevent = {
- .name = "lguest",
- .features = CLOCK_EVT_FEAT_ONESHOT,
- .set_next_event = lguest_clockevent_set_next_event,
- .set_mode = lguest_clockevent_set_mode,
- .rating = INT_MAX,
- .mult = 1,
- .shift = 0,
- .min_delta_ns = LG_CLOCK_MIN_DELTA,
- .max_delta_ns = LG_CLOCK_MAX_DELTA,
-};
-
-/* This is the Guest timer interrupt handler (hardware interrupt 0). We just
- * call the clockevent infrastructure and it does whatever needs doing. */
-static void lguest_time_irq(unsigned int irq, struct irq_desc *desc)
-{
- unsigned long flags;
-
- /* Don't interrupt us while this is running. */
- local_irq_save(flags);
- lguest_clockevent.event_handler(&lguest_clockevent);
- local_irq_restore(flags);
-}
-
-/* At some point in the boot process, we get asked to set up our timing
- * infrastructure. The kernel doesn't expect timer interrupts before this, but
- * we cleverly initialized the "blocked_interrupts" field of "struct
- * lguest_data" so that timer interrupts were blocked until now. */
-static void lguest_time_init(void)
-{
- /* Set up the timer interrupt (0) to go to our simple timer routine */
- set_irq_handler(0, lguest_time_irq);
-
- /* Our clock structure look like arch/i386/kernel/tsc.c if we can use
- * the TSC, otherwise it's a dumb nanosecond-resolution clock. Either
- * way, the "rating" is initialized so high that it's always chosen
- * over any other clocksource. */
- if (lguest_data.tsc_khz)
- lguest_clock.mult = clocksource_khz2mult(lguest_data.tsc_khz,
- lguest_clock.shift);
- clock_base = lguest_clock_read();
- clocksource_register(&lguest_clock);
-
- /* Now we've set up our clock, we can use it as the scheduler clock */
- pv_time_ops.sched_clock = lguest_sched_clock;
-
- /* We can't set cpumask in the initializer: damn C limitations! Set it
- * here and register our timer device. */
- lguest_clockevent.cpumask = cpumask_of_cpu(0);
- clockevents_register_device(&lguest_clockevent);
-
- /* Finally, we unblock the timer interrupt. */
- enable_lguest_irq(0);
-}
-
-/*
- * Miscellaneous bits and pieces.
- *
- * Here is an oddball collection of functions which the Guest needs for things
- * to work. They're pretty simple.
- */
-
-/* The Guest needs to tell the host what stack it expects traps to use. For
- * native hardware, this is part of the Task State Segment mentioned above in
- * lguest_load_tr_desc(), but to help hypervisors there's this special call.
- *
- * We tell the Host the segment we want to use (__KERNEL_DS is the kernel data
- * segment), the privilege level (we're privilege level 1, the Host is 0 and
- * will not tolerate us trying to use that), the stack pointer, and the number
- * of pages in the stack. */
-static void lguest_load_esp0(struct tss_struct *tss,
- struct thread_struct *thread)
-{
- lazy_hcall(LHCALL_SET_STACK, __KERNEL_DS|0x1, thread->esp0,
- THREAD_SIZE/PAGE_SIZE);
-}
-
-/* Let's just say, I wouldn't do debugging under a Guest. */
-static void lguest_set_debugreg(int regno, unsigned long value)
-{
- /* FIXME: Implement */
-}
-
-/* There are times when the kernel wants to make sure that no memory writes are
- * caught in the cache (that they've all reached real hardware devices). This
- * doesn't matter for the Guest which has virtual hardware.
- *
- * On the Pentium 4 and above, cpuid() indicates that the Cache Line Flush
- * (clflush) instruction is available and the kernel uses that. Otherwise, it
- * uses the older "Write Back and Invalidate Cache" (wbinvd) instruction.
- * Unlike clflush, wbinvd can only be run at privilege level 0. So we can
- * ignore clflush, but replace wbinvd.
- */
-static void lguest_wbinvd(void)
-{
-}
-
-/* If the Guest expects to have an Advanced Programmable Interrupt Controller,
- * we play dumb by ignoring writes and returning 0 for reads. So it's no
- * longer Programmable nor Controlling anything, and I don't think 8 lines of
- * code qualifies for Advanced. It will also never interrupt anything. It
- * does, however, allow us to get through the Linux boot code. */
-#ifdef CONFIG_X86_LOCAL_APIC
-static void lguest_apic_write(unsigned long reg, unsigned long v)
-{
-}
-
-static unsigned long lguest_apic_read(unsigned long reg)
-{
- return 0;
-}
-#endif
-
-/* STOP! Until an interrupt comes in. */
-static void lguest_safe_halt(void)
-{
- hcall(LHCALL_HALT, 0, 0, 0);
-}
-
-/* Perhaps CRASH isn't the best name for this hypercall, but we use it to get a
- * message out when we're crashing as well as elegant termination like powering
- * off.
- *
- * Note that the Host always prefers that the Guest speak in physical addresses
- * rather than virtual addresses, so we use __pa() here. */
-static void lguest_power_off(void)
-{
- hcall(LHCALL_CRASH, __pa("Power down"), 0, 0);
-}
-
-/*
- * Panicing.
- *
- * Don't. But if you did, this is what happens.
- */
-static int lguest_panic(struct notifier_block *nb, unsigned long l, void *p)
-{
- hcall(LHCALL_CRASH, __pa(p), 0, 0);
- /* The hcall won't return, but to keep gcc happy, we're "done". */
- return NOTIFY_DONE;
-}
-
-static struct notifier_block paniced = {
- .notifier_call = lguest_panic
-};
-
-/* Setting up memory is fairly easy. */
-static __init char *lguest_memory_setup(void)
-{
- /* We do this here and not earlier because lockcheck barfs if we do it
- * before start_kernel() */
- atomic_notifier_chain_register(&panic_notifier_list, &paniced);
-
- /* The Linux bootloader header contains an "e820" memory map: the
- * Launcher populated the first entry with our memory limit. */
- add_memory_region(boot_params.e820_map[0].addr,
- boot_params.e820_map[0].size,
- boot_params.e820_map[0].type);
-
- /* This string is for the boot messages. */
- return "LGUEST";
-}
-
-/*G:050
- * Patching (Powerfully Placating Performance Pedants)
- *
- * We have already seen that pv_ops structures let us replace simple
- * native instructions with calls to the appropriate back end all throughout
- * the kernel. This allows the same kernel to run as a Guest and as a native
- * kernel, but it's slow because of all the indirect branches.
- *
- * Remember that David Wheeler quote about "Any problem in computer science can
- * be solved with another layer of indirection"? The rest of that quote is
- * "... But that usually will create another problem." This is the first of
- * those problems.
- *
- * Our current solution is to allow the paravirt back end to optionally patch
- * over the indirect calls to replace them with something more efficient. We
- * patch the four most commonly called functions: disable interrupts, enable
- * interrupts, restore interrupts and save interrupts. We usually have 10
- * bytes to patch into: the Guest versions of these operations are small enough
- * that we can fit comfortably.
- *
- * First we need assembly templates of each of the patchable Guest operations,
- * and these are in lguest_asm.S. */
-
-/*G:060 We construct a table from the assembler templates: */
-static const struct lguest_insns
-{
- const char *start, *end;
-} lguest_insns[] = {
- [PARAVIRT_PATCH(pv_irq_ops.irq_disable)] = { lgstart_cli, lgend_cli },
- [PARAVIRT_PATCH(pv_irq_ops.irq_enable)] = { lgstart_sti, lgend_sti },
- [PARAVIRT_PATCH(pv_irq_ops.restore_fl)] = { lgstart_popf, lgend_popf },
- [PARAVIRT_PATCH(pv_irq_ops.save_fl)] = { lgstart_pushf, lgend_pushf },
-};
-
-/* Now our patch routine is fairly simple (based on the native one in
- * paravirt.c). If we have a replacement, we copy it in and return how much of
- * the available space we used. */
-static unsigned lguest_patch(u8 type, u16 clobber, void *ibuf,
- unsigned long addr, unsigned len)
-{
- unsigned int insn_len;
-
- /* Don't do anything special if we don't have a replacement */
- if (type >= ARRAY_SIZE(lguest_insns) || !lguest_insns[type].start)
- return paravirt_patch_default(type, clobber, ibuf, addr, len);
-
- insn_len = lguest_insns[type].end - lguest_insns[type].start;
-
- /* Similarly if we can't fit replacement (shouldn't happen, but let's
- * be thorough). */
- if (len < insn_len)
- return paravirt_patch_default(type, clobber, ibuf, addr, len);
-
- /* Copy in our instructions. */
- memcpy(ibuf, lguest_insns[type].start, insn_len);
- return insn_len;
-}
-
-/*G:030 Once we get to lguest_init(), we know we're a Guest. The pv_ops
- * structures in the kernel provide points for (almost) every routine we have
- * to override to avoid privileged instructions. */
-__init void lguest_init(void *boot)
-{
- /* Copy boot parameters first: the Launcher put the physical location
- * in %esi, and head.S converted that to a virtual address and handed
- * it to us. We use "__memcpy" because "memcpy" sometimes tries to do
- * tricky things to go faster, and we're not ready for that. */
- __memcpy(&boot_params, boot, PARAM_SIZE);
- /* The boot parameters also tell us where the command-line is: save
- * that, too. */
- __memcpy(boot_command_line, __va(boot_params.hdr.cmd_line_ptr),
- COMMAND_LINE_SIZE);
-
- /* We're under lguest, paravirt is enabled, and we're running at
- * privilege level 1, not 0 as normal. */
- pv_info.name = "lguest";
- pv_info.paravirt_enabled = 1;
- pv_info.kernel_rpl = 1;
-
- /* We set up all the lguest overrides for sensitive operations. These
- * are detailed with the operations themselves. */
-
- /* interrupt-related operations */
- pv_irq_ops.init_IRQ = lguest_init_IRQ;
- pv_irq_ops.save_fl = save_fl;
- pv_irq_ops.restore_fl = restore_fl;
- pv_irq_ops.irq_disable = irq_disable;
- pv_irq_ops.irq_enable = irq_enable;
- pv_irq_ops.safe_halt = lguest_safe_halt;
-
- /* init-time operations */
- pv_init_ops.memory_setup = lguest_memory_setup;
- pv_init_ops.patch = lguest_patch;
-
- /* Intercepts of various cpu instructions */
- pv_cpu_ops.load_gdt = lguest_load_gdt;
- pv_cpu_ops.cpuid = lguest_cpuid;
- pv_cpu_ops.load_idt = lguest_load_idt;
- pv_cpu_ops.iret = lguest_iret;
- pv_cpu_ops.load_esp0 = lguest_load_esp0;
- pv_cpu_ops.load_tr_desc = lguest_load_tr_desc;
- pv_cpu_ops.set_ldt = lguest_set_ldt;
- pv_cpu_ops.load_tls = lguest_load_tls;
- pv_cpu_ops.set_debugreg = lguest_set_debugreg;
- pv_cpu_ops.clts = lguest_clts;
- pv_cpu_ops.read_cr0 = lguest_read_cr0;
- pv_cpu_ops.write_cr0 = lguest_write_cr0;
- pv_cpu_ops.read_cr4 = lguest_read_cr4;
- pv_cpu_ops.write_cr4 = lguest_write_cr4;
- pv_cpu_ops.write_gdt_entry = lguest_write_gdt_entry;
- pv_cpu_ops.write_idt_entry = lguest_write_idt_entry;
- pv_cpu_ops.wbinvd = lguest_wbinvd;
- pv_cpu_ops.lazy_mode.enter = paravirt_enter_lazy_cpu;
- pv_cpu_ops.lazy_mode.leave = lguest_leave_lazy_mode;
-
- /* pagetable management */
- pv_mmu_ops.write_cr3 = lguest_write_cr3;
- pv_mmu_ops.flush_tlb_user = lguest_flush_tlb_user;
- pv_mmu_ops.flush_tlb_single = lguest_flush_tlb_single;
- pv_mmu_ops.flush_tlb_kernel = lguest_flush_tlb_kernel;
- pv_mmu_ops.set_pte = lguest_set_pte;
- pv_mmu_ops.set_pte_at = lguest_set_pte_at;
- pv_mmu_ops.set_pmd = lguest_set_pmd;
- pv_mmu_ops.read_cr2 = lguest_read_cr2;
- pv_mmu_ops.read_cr3 = lguest_read_cr3;
- pv_mmu_ops.lazy_mode.enter = paravirt_enter_lazy_mmu;
- pv_mmu_ops.lazy_mode.leave = lguest_leave_lazy_mode;
-
-#ifdef CONFIG_X86_LOCAL_APIC
- /* apic read/write intercepts */
- pv_apic_ops.apic_write = lguest_apic_write;
- pv_apic_ops.apic_write_atomic = lguest_apic_write;
- pv_apic_ops.apic_read = lguest_apic_read;
-#endif
-
- /* time operations */
- pv_time_ops.get_wallclock = lguest_get_wallclock;
- pv_time_ops.time_init = lguest_time_init;
-
- /* Now is a good time to look at the implementations of these functions
- * before returning to the rest of lguest_init(). */
-
- /*G:070 Now we've seen all the paravirt_ops, we return to
- * lguest_init() where the rest of the fairly chaotic boot setup
- * occurs.
- *
- * The Host expects our first hypercall to tell it where our "struct
- * lguest_data" is, so we do that first. */
- hcall(LHCALL_LGUEST_INIT, __pa(&lguest_data), 0, 0);
-
- /* The native boot code sets up initial page tables immediately after
- * the kernel itself, and sets init_pg_tables_end so they're not
- * clobbered. The Launcher places our initial pagetables somewhere at
- * the top of our physical memory, so we don't need extra space: set
- * init_pg_tables_end to the end of the kernel. */
- init_pg_tables_end = __pa(pg0);
-
- /* Load the %fs segment register (the per-cpu segment register) with
- * the normal data segment to get through booting. */
- asm volatile ("mov %0, %%fs" : : "r" (__KERNEL_DS) : "memory");
-
- /* Clear the part of the kernel data which is expected to be zero.
- * Normally it will be anyway, but if we're loading from a bzImage with
- * CONFIG_RELOCATALE=y, the relocations will be sitting here. */
- memset(__bss_start, 0, __bss_stop - __bss_start);
-
- /* The Host uses the top of the Guest's virtual address space for the
- * Host<->Guest Switcher, and it tells us how much it needs in
- * lguest_data.reserve_mem, set up on the LGUEST_INIT hypercall. */
- reserve_top_address(lguest_data.reserve_mem);
-
- /* If we don't initialize the lock dependency checker now, it crashes
- * paravirt_disable_iospace. */
- lockdep_init();
-
- /* The IDE code spends about 3 seconds probing for disks: if we reserve
- * all the I/O ports up front it can't get them and so doesn't probe.
- * Other device drivers are similar (but less severe). This cuts the
- * kernel boot time on my machine from 4.1 seconds to 0.45 seconds. */
- paravirt_disable_iospace();
-
- /* This is messy CPU setup stuff which the native boot code does before
- * start_kernel, so we have to do, too: */
- cpu_detect(&new_cpu_data);
- /* head.S usually sets up the first capability word, so do it here. */
- new_cpu_data.x86_capability[0] = cpuid_edx(1);
-
- /* Math is always hard! */
- new_cpu_data.hard_math = 1;
-
-#ifdef CONFIG_X86_MCE
- mce_disabled = 1;
-#endif
-#ifdef CONFIG_ACPI
- acpi_disabled = 1;
- acpi_ht = 0;
-#endif
-
- /* We set the perferred console to "hvc". This is the "hypervisor
- * virtual console" driver written by the PowerPC people, which we also
- * adapted for lguest's use. */
- add_preferred_console("hvc", 0, NULL);
-
- /* Last of all, we set the power management poweroff hook to point to
- * the Guest routine to power off. */
- pm_power_off = lguest_power_off;
-
- /* Now we're set up, call start_kernel() in init/main.c and we proceed
- * to boot as normal. It never returns. */
- start_kernel();
-}
-/*
- * This marks the end of stage II of our journey, The Guest.
- *
- * It is now time for us to explore the nooks and crannies of the three Guest
- * devices and complete our understanding of the Guest in "make Drivers".
- */
+++ /dev/null
-#include <linux/linkage.h>
-#include <linux/lguest.h>
-#include <asm/asm-offsets.h>
-#include <asm/thread_info.h>
-#include <asm/processor-flags.h>
-
-/*G:020 This is where we begin: we have a magic signature which the launcher
- * looks for. The plan is that the Linux boot protocol will be extended with a
- * "platform type" field which will guide us here from the normal entry point,
- * but for the moment this suffices. The normal boot code uses %esi for the
- * boot header, so we do too. We convert it to a virtual address by adding
- * PAGE_OFFSET, and hand it to lguest_init() as its argument (ie. %eax).
- *
- * The .section line puts this code in .init.text so it will be discarded after
- * boot. */
-.section .init.text, "ax", @progbits
-.ascii "GenuineLguest"
- /* Set up initial stack. */
- movl $(init_thread_union+THREAD_SIZE),%esp
- movl %esi, %eax
- addl $__PAGE_OFFSET, %eax
- jmp lguest_init
-
-/*G:055 We create a macro which puts the assembler code between lgstart_ and
- * lgend_ markers. These templates are put in the .text section: they can't be
- * discarded after boot as we may need to patch modules, too. */
-.text
-#define LGUEST_PATCH(name, insns...) \
- lgstart_##name: insns; lgend_##name:; \
- .globl lgstart_##name; .globl lgend_##name
-
-LGUEST_PATCH(cli, movl $0, lguest_data+LGUEST_DATA_irq_enabled)
-LGUEST_PATCH(sti, movl $X86_EFLAGS_IF, lguest_data+LGUEST_DATA_irq_enabled)
-LGUEST_PATCH(popf, movl %eax, lguest_data+LGUEST_DATA_irq_enabled)
-LGUEST_PATCH(pushf, movl lguest_data+LGUEST_DATA_irq_enabled, %eax)
-/*:*/
-
-/* These demark the EIP range where host should never deliver interrupts. */
-.global lguest_noirq_start
-.global lguest_noirq_end
-
-/*M:004 When the Host reflects a trap or injects an interrupt into the Guest,
- * it sets the eflags interrupt bit on the stack based on
- * lguest_data.irq_enabled, so the Guest iret logic does the right thing when
- * restoring it. However, when the Host sets the Guest up for direct traps,
- * such as system calls, the processor is the one to push eflags onto the
- * stack, and the interrupt bit will be 1 (in reality, interrupts are always
- * enabled in the Guest).
- *
- * This turns out to be harmless: the only trap which should happen under Linux
- * with interrupts disabled is Page Fault (due to our lazy mapping of vmalloc
- * regions), which has to be reflected through the Host anyway. If another
- * trap *does* go off when interrupts are disabled, the Guest will panic, and
- * we'll never get to this iret! :*/
-
-/*G:045 There is one final paravirt_op that the Guest implements, and glancing
- * at it you can see why I left it to last. It's *cool*! It's in *assembler*!
- *
- * The "iret" instruction is used to return from an interrupt or trap. The
- * stack looks like this:
- * old address
- * old code segment & privilege level
- * old processor flags ("eflags")
- *
- * The "iret" instruction pops those values off the stack and restores them all
- * at once. The only problem is that eflags includes the Interrupt Flag which
- * the Guest can't change: the CPU will simply ignore it when we do an "iret".
- * So we have to copy eflags from the stack to lguest_data.irq_enabled before
- * we do the "iret".
- *
- * There are two problems with this: firstly, we need to use a register to do
- * the copy and secondly, the whole thing needs to be atomic. The first
- * problem is easy to solve: push %eax on the stack so we can use it, and then
- * restore it at the end just before the real "iret".
- *
- * The second is harder: copying eflags to lguest_data.irq_enabled will turn
- * interrupts on before we're finished, so we could be interrupted before we
- * return to userspace or wherever. Our solution to this is to surround the
- * code with lguest_noirq_start: and lguest_noirq_end: labels. We tell the
- * Host that it is *never* to interrupt us there, even if interrupts seem to be
- * enabled. */
-ENTRY(lguest_iret)
- pushl %eax
- movl 12(%esp), %eax
-lguest_noirq_start:
- /* Note the %ss: segment prefix here. Normal data accesses use the
- * "ds" segment, but that will have already been restored for whatever
- * we're returning to (such as userspace): we can't trust it. The %ss:
- * prefix makes sure we use the stack segment, which is still valid. */
- movl %eax,%ss:lguest_data+LGUEST_DATA_irq_enabled
- popl %eax
- iret
-lguest_noirq_end:
projects / cascardo / linux.git / commitdiff