x86/efi: Always map the first physical page into the EFI pagetables

[mirror_ubuntu-artful-kernel.git] / arch / x86 / platform / efi / efi_64.c

diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 319148bd4b05091d24576a7535b10aad7bec0c2d..2f25a363068cf9723e8b418e8c1942a6d3ca4029 100644 (file)
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -268,6 +268,22 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
 
        efi_scratch.use_pgd = true;
 
+       /*
+        * Certain firmware versions are way too sentimential and still believe
+        * they are exclusive and unquestionable owners of the first physical page,
+        * even though they explicitly mark it as EFI_CONVENTIONAL_MEMORY
+        * (but then write-access it later during SetVirtualAddressMap()).
+        *
+        * Create a 1:1 mapping for this page, to avoid triple faults during early
+        * boot with such firmware. We are free to hand this page to the BIOS,
+        * as trim_bios_range() will reserve the first page and isolate it away
+        * from memory allocators anyway.
+        */
+       if (kernel_map_pages_in_pgd(pgd, 0x0, 0x0, 1, _PAGE_RW)) {
+               pr_err("Failed to create 1:1 mapping for the first page!\n");
+               return 1;
+       }
+
        /*
         * When making calls to the firmware everything needs to be 1:1
         * mapped and addressable with 32-bit pointers. Map the kernel