• Andrea Arcangeli's avatar
    Revert "x86, mm: Make spurious_fault check explicitly check explicitly check the PRESENT bit" · 954f8571
    Andrea Arcangeli authored
    I got a report for a minor regression introduced by commit
    027ef6c8 ("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 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
    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: default avatarAndrea 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: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
    954f8571
fault.c 29 KB