x86/efi: Allocate a trampoline if needed in efi_free_boot_services()

[cascardo/linux.git] / arch / x86 / platform / efi / quirks.c

diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
index 4480c06..89d1146 100644 (file)
--- a/arch/x86/platform/efi/quirks.c
+++ b/arch/x86/platform/efi/quirks.c
@@ -254,6 +254,7 @@ void __init efi_free_boot_services(void)
        for_each_efi_memory_desc(md) {
                unsigned long long start = md->phys_addr;
                unsigned long long size = md->num_pages << EFI_PAGE_SHIFT;
+               size_t rm_size;
 
                if (md->type != EFI_BOOT_SERVICES_CODE &&
                    md->type != EFI_BOOT_SERVICES_DATA)
@@ -263,6 +264,26 @@ void __init efi_free_boot_services(void)
                if (md->attribute & EFI_MEMORY_RUNTIME)
                        continue;
 
+               /*
+                * Nasty quirk: if all sub-1MB memory is used for boot
+                * services, we can get here without having allocated the
+                * real mode trampoline.  It's too late to hand boot services
+                * memory back to the memblock allocator, so instead
+                * try to manually allocate the trampoline if needed.
+                *
+                * I've seen this on a Dell XPS 13 9350 with firmware
+                * 1.4.4 with SGX enabled booting Linux via Fedora 24's
+                * grub2-efi on a hard disk.  (And no, I don't know why
+                * this happened, but Linux should still try to boot rather
+                * panicing early.)
+                */
+               rm_size = real_mode_size_needed();
+               if (rm_size && (start + rm_size) < (1<<20) && size >= rm_size) {
+                       set_real_mode_mem(start, rm_size);
+                       start += rm_size;
+                       size -= rm_size;
+               }
+
                free_bootmem_late(start, size);
        }