1 files changed, 21 insertions, 0 deletions

diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
index 4480c06cade7..89d1146f5a6f 100644
--- 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);
         }