The patch titled
Subject: x86/mm: limit extra padding calculation to x86_32
has been added to the -mm tree. Its filename is
x86-mm-limit-2-4m-size-calculation-to-x86_32.patch
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From: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
Subject: x86/mm: limit extra padding calculation to x86_32
Starting with kernel v3.5 kexec based crash dumping was observed to fail
(without any apparent message) on x86_64 machines. This was traced to a
lack of memory triggered by a substantial increase (several megabyes) in
the size of the initial page tables.
After regression (on a VM with 2GB of memory):
kernel direct mapping tables up to 0x7fffcfff @ [mem 0x1fbfd000-0x1fffffff]
size = 4206591 bytes
With this patch applied:
kernel direct mapping tables up to 0x7fffcfff @ [mem 0x1fffc000-0x1fffffff]
size = 16383 bytes
A bisection lead to commit 722bc6b ("x86/mm: Fix the size calculation of
mapping tables")
This change modified the extra space calculation to take into account that
the first 2/4M range of memory would be mapped as 4K pages as suggested in
chapter 11.11.9 of the Intel software developer's manual.
However this is currently only true for x86_32 (the reasons behind that
are unclear but apparently the whole page table setup needs to be re-
visited as it turns out to be very easy to break and has flaws in its
current form).
Until the logic can be revisited and combined, pair up the extra space
calculation with the logic which creates the extra mappings.
Signed-off-by: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
Cc: WANG Cong <xiyou.wangcong@xxxxxxxxx>
Cc: Yinghai Lu <yinghai@xxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [v3.5+]
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/x86/mm/init.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff -puN arch/x86/mm/init.c~x86-mm-limit-2-4m-size-calculation-to-x86_32 arch/x86/mm/init.c
--- a/arch/x86/mm/init.c~x86-mm-limit-2-4m-size-calculation-to-x86_32
+++ a/arch/x86/mm/init.c
@@ -60,10 +60,11 @@ static void __init find_early_table_spac
extra = end - ((end>>PMD_SHIFT) << PMD_SHIFT);
#ifdef CONFIG_X86_32
extra += PMD_SIZE;
-#endif
+
/* The first 2/4M doesn't use large pages. */
if (mr->start < PMD_SIZE)
extra += mr->end - mr->start;
+#endif
ptes = (extra + PAGE_SIZE - 1) >> PAGE_SHIFT;
} else
_
Patches currently in -mm which might be from stefan.bader@xxxxxxxxxxxxx are
x86-mm-limit-2-4m-size-calculation-to-x86_32.patch
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