From 737a5ebdd7ac1f4106cb0b0c53cc8f73b6ff1aca Mon Sep 17 00:00:00 2001 From: Stefan Bader Date: Fri, 13 Jul 2012 15:16:33 +0200 Subject: [PATCH] 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 the commit below: 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 Cc: stable@vger.kernel.org # v3.5+ Cc: WANG Cong Cc: Yinghai Lu Cc: Tejun Heo --- arch/x86/mm/init.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c index bc4e9d8..636bbfd 100644 --- a/arch/x86/mm/init.c +++ b/arch/x86/mm/init.c @@ -60,10 +60,11 @@ static void __init find_early_table_space(struct map_range *mr, unsigned long en 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 -- 1.7.9.5