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authorAndrea Arcangeli <aarcange@redhat.com>2013-02-22 15:11:49 -0800
committerIngo Molnar <mingo@kernel.org>2013-02-24 13:01:44 +0100
commit954f857187033ee3d3704a8206715cf354c38898 (patch)
tree0298d5fa15655bcddc19200bc86eed34f34c0ced /arch/x86/mm
parent942670d0dc41b5fe9b735c31ca9234d80729bf7e (diff)
Revert "x86, mm: Make spurious_fault check explicitly check explicitly check the PRESENT bit"
I got a report for a minor regression introduced by commit 027ef6c87853b ("mm: thp: fix pmd_present for split_huge_page and PROT_NONE with THP"). So the problem is, pageattr creates kernel pagetables (pte and pmds) that breaks pte_present/pmd_present and the patch above exposed this invariant breakage for pmd_present. The same problem already existed for the pte and pte_present and it was fixed by commit 660a293ea9be709 ("x86, mm: Make spurious_fault check explicitly check the PRESENT bit") (if it wasn't for that commit, it wouldn't even be a regression). That fix avoids the pagefault to use pte_present. I could follow through by stopping using pmd_present/pmd_huge too. However I think it's more robust to fix pageattr and to clear the PSE/GLOBAL bitflags too in addition to the present bitflag. So the kernel page fault can keep using the regular pte_present/pmd_present/pmd_huge. The confusion arises because _PAGE_GLOBAL and _PAGE_PROTNONE are sharing the same bit, and in the pmd case we pretend _PAGE_PSE to be set only in present pmds (to facilitate split_huge_page final tlb flush). Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Cc: Andi Kleen <andi@firstfloor.org> Cc: Shaohua Li <shaohua.li@intel.com> Cc: "H. Peter Anvin" <hpa@linux.intel.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Hugh Dickins <hughd@google.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/mm')
-rw-r--r--arch/x86/mm/fault.c8
1 files changed, 1 insertions, 7 deletions
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index fb674fd3fc2..2b97525246d 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -939,14 +939,8 @@ spurious_fault(unsigned long error_code, unsigned long address)
if (pmd_large(*pmd))
return spurious_fault_check(error_code, (pte_t *) pmd);
- /*
- * Note: don't use pte_present() here, since it returns true
- * if the _PAGE_PROTNONE bit is set. However, this aliases the
- * _PAGE_GLOBAL bit, which for kernel pages give false positives
- * when CONFIG_DEBUG_PAGEALLOC is used.
- */
pte = pte_offset_kernel(pmd, address);
- if (!(pte_flags(*pte) & _PAGE_PRESENT))
+ if (!pte_present(*pte))
return 0;
ret = spurious_fault_check(error_code, pte);