Commit 954f8571 authored by Andrea Arcangeli's avatar Andrea Arcangeli Committed by Ingo Molnar
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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
027ef6c8 ("mm: thp: fix pmd_present for split_huge_page and

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 660a293e

 ("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

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: default avatarAndrea Arcangeli <>
Cc: Andi Kleen <>
Cc: Shaohua Li <>
Cc: "H. Peter Anvin" <>
Cc: Mel Gorman <>
Cc: Hugh Dickins <>
Cc: Andrew Morton <>
Cc: Peter Zijlstra <>
Cc: Thomas Gleixner <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarIngo Molnar <>
parent 942670d0
......@@ -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
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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