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

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>

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 3412c45..740f3bd 100644 (file)
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -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));
 }