The patch titled
Subject: Revert "x86, mm: Make spurious_fault check explicitly check the PRESENT bit"
has been added to the -mm tree. Its filename is
revert-x86-mm-make-spurious_fault-check-explicitly-check-the-present-bit.patch
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From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Subject: Revert "x86, mm: Make spurious_fault 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).
This patch:
Revert commit 660a293ea9be709 ("x86, mm: Make spurious_fault check
explicitly check the PRESENT bit").
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: Ingo Molnar <mingo@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/x86/mm/fault.c | 8 +-------
1 file changed, 1 insertion(+), 7 deletions(-)
diff -puN arch/x86/mm/fault.c~revert-x86-mm-make-spurious_fault-check-explicitly-check-the-present-bit arch/x86/mm/fault.c
--- a/arch/x86/mm/fault.c~revert-x86-mm-make-spurious_fault-check-explicitly-check-the-present-bit
+++ a/arch/x86/mm/fault.c
@@ -937,14 +937,8 @@ spurious_fault(unsigned long error_code,
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);
_
Patches currently in -mm which might be from aarcange@xxxxxxxxxx are
linux-next.patch
mm-migrate-check-page_count-of-thp-before-migrating.patch
revert-x86-mm-make-spurious_fault-check-explicitly-check-the-present-bit.patch
pageattr-prevent-pse-and-gloabl-leftovers-to-confuse-pmd-pte_present-and-pmd_huge.patch
audit-create-explicit-audit_seccomp-event-type.patch
audit-catch-possible-null-audit-buffers.patch
mm-huge_memory-use-new-hashtable-implementation.patch
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