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Subject[PATCH 5.10 15/57] Revert "x86/setup: dont remove E820_TYPE_RAM for pfn 0"
Date
From: Mike Rapoport <rppt@linux.ibm.com>

commit 5c279c4cf206e03995e04fd3404fa95ffd243a97 upstream.

This reverts commit bde9cfa3afe4324ec251e4af80ebf9b7afaf7afe.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kernel/setup.c | 20 +++++++++++---------
1 file changed, 11 insertions(+), 9 deletions(-)

--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -666,6 +666,17 @@ static void __init trim_platform_memory_
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.
* take them out.
@@ -722,15 +733,6 @@ early_param("reservelow", parse_reservel

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));
}


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