Commit-ID: 954f857187033ee3d3704a8206715cf354c38898
Gitweb: http://git.kernel.org/tip/954f857187033ee3d3704a8206715cf354c38898
Author: Andrea Arcangeli <aarcange@xxxxxxxxxx>
AuthorDate: Fri, 22 Feb 2013 15:11:49 -0800
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Sun, 24 Feb 2013 13:01:44 +0100
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@xxxxxxxxxx>
Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
Cc: Shaohua Li <shaohua.li@xxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/mm/fault.c | 8 +-------
1 file changed, 1 insertion(+), 7 deletions(-)
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index fb674fd..2b97525 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);
--
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