linux/arch/x86/platform/efi
Mike Rapoport f1d4d47c58 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: a799c2bd29 ("x86/setup: Consolidate early memory reservations")
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Hugh Dickins <hughd@google.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=213177
Link: https://lkml.kernel.org/r/20210601075354.5149-2-rppt@kernel.org
2021-06-03 19:57:55 +02:00
..
efi_32.c efi/x86: Move 32-bit code into efi_32.c 2020-08-20 11:18:36 +02:00
efi_64.c x86/sev-es: Rename sev-es.{ch} to sev.{ch} 2021-05-10 07:40:27 +02:00
efi_stub_32.S efi/x86: Preserve %ebx correctly in efi_set_virtual_address_map() 2020-03-08 09:58:23 +01:00
efi_stub_64.S x86: Change {JMP,CALL}_NOSPEC argument 2020-04-30 20:14:34 +02:00
efi_thunk_64.S efi: x86: move mixed mode stack PA variable out of 'efi_scratch' 2021-01-19 17:57:16 +01:00
efi.c Merge branch 'efi/urgent' into efi/core, to pick up fixes 2020-10-12 13:38:31 +02:00
Makefile efi/x86: Disable instrumentation in the EFI runtime handling code 2020-01-25 10:14:37 +01:00
quirks.c x86/setup: Always reserve the first 1M of RAM 2021-06-03 19:57:55 +02:00