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Revert "x86/setup: don't remove E820_TYPE_RAM for pfn 0" 

This reverts commit bde9cfa3af.

Changing the first memory page type from E820_TYPE_RESERVED to
E820_TYPE_RAM makes it a part of "System RAM" resource rather than a
reserved resource and this in turn causes devmem_is_allowed() to treat
is as area that can be accessed but it is filled with zeroes instead of
the actual data as previously.

The change in /dev/mem output causes lilo to fail as was reported at
slakware users forum, and probably other legacy applications will
experience similar problems.

Link: https://www.linuxquestions.org/questions/slackware-14/slackware-current-lilo-vesa-warnings-after-recent-updates-4175689617/#post6214439
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Mike Rapoport 2021-02-04 20:12:37 +02:00 committed by Linus Torvalds
parent 927002ed29
commit 5c279c4cf2
1 changed files with 11 additions and 9 deletions
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20
arch/x86/kernel/setup.c
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@ -660,6 +660,17 @@ static void __init trim_platform_memory_ranges(void)
static void __init trim_bios_range(void)
{
/*
* A special case is the first 4Kb of memory;
* This is a BIOS owned area, not kernel ram, but generally
* not listed as such in the E820 table.
*
* This typically reserves additional memory (64KiB by default)
* since some BIOSes are known to corrupt low memory. See the
* Kconfig help text for X86_RESERVE_LOW.
*/
e820__range_update(0, PAGE_SIZE, E820_TYPE_RAM, E820_TYPE_RESERVED);
/*
* special case: Some BIOSes report the PC BIOS
* area (640Kb -> 1Mb) as RAM even though it is not.
@ -717,15 +728,6 @@ early_param("reservelow", parse_reservelow);
static void __init trim_low_memory_range(void)
{
/*
* A special case is the first 4Kb of memory;
* This is a BIOS owned area, not kernel ram, but generally
* not listed as such in the E820 table.
*
* This typically reserves additional memory (64KiB by default)
* since some BIOSes are known to corrupt low memory. See the
* Kconfig help text for X86_RESERVE_LOW.
*/
memblock_reserve(0, ALIGN(reserve_low, PAGE_SIZE));
}