}
/*H:210
- * The set_guest_interrupt() routine actually delivers the interrupt or
- * trap. The mechanics of delivering traps and interrupts to the Guest are the
- * same, except some traps have an "error code" which gets pushed onto the
- * stack as well: the caller tells us if this is one.
- *
- * "lo" and "hi" are the two parts of the Interrupt Descriptor Table for this
- * interrupt or trap. It's split into two parts for traditional reasons: gcc
- * on i386 used to be frightened by 64 bit numbers.
+ * The push_guest_interrupt_stack() routine saves Guest state on the stack for
+ * an interrupt or trap. The mechanics of delivering traps and interrupts to
+ * the Guest are the same, except some traps have an "error code" which gets
+ * pushed onto the stack as well: the caller tells us if this is one.
*
* We set up the stack just like the CPU does for a real interrupt, so it's
* identical for the Guest (and the standard "iret" instruction will undo
* it).
*/
-static void set_guest_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi,
- bool has_err)
+static void push_guest_interrupt_stack(struct lg_cpu *cpu, bool has_err)
{
unsigned long gstack, origstack;
u32 eflags, ss, irq_enable;
if (has_err)
push_guest_stack(cpu, &gstack, cpu->regs->errcode);
- /*
- * Now we've pushed all the old state, we change the stack, the code
- * segment and the address to execute.
- */
+ /* Adjust the stack pointer and stack segment. */
cpu->regs->ss = ss;
cpu->regs->esp = virtstack + (gstack - origstack);
+}
+
+/*
+ * This actually makes the Guest start executing the given interrupt/trap
+ * handler.
+ *
+ * "lo" and "hi" are the two parts of the Interrupt Descriptor Table for this
+ * interrupt or trap. It's split into two parts for traditional reasons: gcc
+ * on i386 used to be frightened by 64 bit numbers.
+ */
+static void guest_run_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi)
+{
+ /* If we're already in the kernel, we don't change stacks. */
+ if ((cpu->regs->ss&0x3) != GUEST_PL)
+ cpu->regs->ss = cpu->esp1;
+
+ /*
+ * Set the code segment and the address to execute.
+ */
cpu->regs->cs = (__KERNEL_CS|GUEST_PL);
cpu->regs->eip = idt_address(lo, hi);
kill_guest(cpu, "Disabling interrupts");
}
+/* This restores the eflags word which was pushed on the stack by a trap */
+static void restore_eflags(struct lg_cpu *cpu)
+{
+ /* This is the physical address of the stack. */
+ unsigned long stack_pa = guest_pa(cpu, cpu->regs->esp);
+
+ /*
+ * Stack looks like this:
+ * Address Contents
+ * esp EIP
+ * esp + 4 CS
+ * esp + 8 EFLAGS
+ */
+ cpu->regs->eflags = lgread(cpu, stack_pa + 8, u32);
+ cpu->regs->eflags &=
+ ~(X86_EFLAGS_TF|X86_EFLAGS_VM|X86_EFLAGS_RF|X86_EFLAGS_NT);
+}
+
/*H:205
* Virtual Interrupts.
*
BUG_ON(irq >= LGUEST_IRQS);
- /*
- * They may be in the middle of an iret, where they asked us never to
- * deliver interrupts.
- */
- if (cpu->regs->eip >= cpu->lg->noirq_start &&
- (cpu->regs->eip < cpu->lg->noirq_end))
- return;
-
/* If they're halted, interrupts restart them. */
if (cpu->halted) {
/* Re-enable interrupts. */
if (idt_present(idt->a, idt->b)) {
/* OK, mark it no longer pending and deliver it. */
clear_bit(irq, cpu->irqs_pending);
+
/*
- * set_guest_interrupt() takes the interrupt descriptor and a
- * flag to say whether this interrupt pushes an error code onto
- * the stack as well: virtual interrupts never do.
+ * They may be about to iret, where they asked us never to
+ * deliver interrupts. In this case, we can emulate that iret
+ * then immediately deliver the interrupt. This is basically
+ * a noop: the iret would pop the interrupt frame and restore
+ * eflags, and then we'd set it up again. So just restore the
+ * eflags word and jump straight to the handler in this case.
+ *
+ * Denys Vlasenko points out that this isn't quite right: if
+ * the iret was returning to userspace, then that interrupt
+ * would reset the stack pointer (which the Guest told us
+ * about via LHCALL_SET_STACK). But unless the Guest is being
+ * *really* weird, that will be the same as the current stack
+ * anyway.
*/
- set_guest_interrupt(cpu, idt->a, idt->b, false);
+ if (cpu->regs->eip == cpu->lg->noirq_iret) {
+ restore_eflags(cpu);
+ } else {
+ /*
+ * set_guest_interrupt() takes a flag to say whether
+ * this interrupt pushes an error code onto the stack
+ * as well: virtual interrupts never do.
+ */
+ push_guest_interrupt_stack(cpu, false);
+ }
+ /* Actually make Guest cpu jump to handler. */
+ guest_run_interrupt(cpu, idt->a, idt->b);
}
/*
*/
if (!idt_present(cpu->arch.idt[num].a, cpu->arch.idt[num].b))
return false;
- set_guest_interrupt(cpu, cpu->arch.idt[num].a,
- cpu->arch.idt[num].b, has_err(num));
+ push_guest_interrupt_stack(cpu, has_err(num));
+ guest_run_interrupt(cpu, cpu->arch.idt[num].a,
+ cpu->arch.idt[num].b);
return true;
}
* The Guest has the ability to turn its interrupt gates into trap gates,
* if it is careful. The Host will let trap gates can go directly to the
* Guest, but the Guest needs the interrupts atomically disabled for an
- * interrupt gate. It can do this by pointing the trap gate at instructions
- * within noirq_start and noirq_end, where it can safely disable interrupts.
+ * interrupt gate. The Host could provide a mechanism to register more
+ * "no-interrupt" regions, and the Guest could point the trap gate at
+ * instructions within that region, where it can safely disable interrupts.
*/
/*M:006
projects / cascardo / linux.git / blobdiff