From f1d4d47c5851b348b7713007e152bc68b94d728b Mon Sep 17 00:00:00 2001 From: Mike Rapoport Date: Tue, 1 Jun 2021 10:53:52 +0300 Subject: x86/setup: Always reserve the first 1M of RAM There are BIOSes that are known to corrupt the memory under 1M, or more precisely under 640K because the memory above 640K is anyway reserved for the EGA/VGA frame buffer and BIOS. To prevent usage of the memory that will be potentially clobbered by the kernel, the beginning of the memory is always reserved. The exact size of the reserved area is determined by CONFIG_X86_RESERVE_LOW build time and the "reservelow=" command line option. The reserved range may be from 4K to 640K with the default of 64K. There are also configurations that reserve the entire 1M range, like machines with SandyBridge graphic devices or systems that enable crash kernel. In addition to the potentially clobbered memory, EBDA of unknown size may be as low as 128K and the memory above that EBDA start is also reserved early. It would have been possible to reserve the entire range under 1M unless for the real mode trampoline that must reside in that area. To accommodate placement of the real mode trampoline and keep the memory safe from being clobbered by BIOS, reserve the first 64K of RAM before memory allocations are possible and then, after the real mode trampoline is allocated, reserve the entire range from 0 to 1M. Update trim_snb_memory() and reserve_real_mode() to avoid redundant reservations of the same memory range. Also make sure the memory under 1M is not getting freed by efi_free_boot_services(). [ bp: Massage commit message and comments. ] Fixes: a799c2bd29d1 ("x86/setup: Consolidate early memory reservations") Signed-off-by: Mike Rapoport Signed-off-by: Borislav Petkov Tested-by: Hugh Dickins Link: https://bugzilla.kernel.org/show_bug.cgi?id=213177 Link: https://lkml.kernel.org/r/20210601075354.5149-2-rppt@kernel.org --- arch/x86/platform/efi/quirks.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'arch/x86/platform/efi') diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c index 7850111008a8..b15ebfe40a73 100644 --- a/arch/x86/platform/efi/quirks.c +++ b/arch/x86/platform/efi/quirks.c @@ -450,6 +450,18 @@ void __init efi_free_boot_services(void) size -= rm_size; } + /* + * Don't free memory under 1M for two reasons: + * - BIOS might clobber it + * - Crash kernel needs it to be reserved + */ + if (start + size < SZ_1M) + continue; + if (start < SZ_1M) { + size -= (SZ_1M - start); + start = SZ_1M; + } + memblock_free_late(start, size); } -- cgit v1.2.3