x86/mm: Only do a local tlb flush in ptep_set_access_flags()

Because we only ever upgrade a PTE when calling ptep_set_access_flags(),
it is safe to skip flushing entries on remote TLBs.

The worst that can happen is a spurious page fault on other CPUs, which
would flush that TLB entry.

Lazily letting another CPU incur a spurious page fault occasionally
is (much!) cheaper than aggressively flushing everybody else's TLB.

Signed-off-by: Rik van Riel <riel@redhat.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 8573b83a63d037bf2f7eb09c8922b94c2b535c45..be3bb4690887e283712a77fb9b6cb23ba5a6b2a1 100644 (file)
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -301,6 +301,13 @@ void pgd_free(struct mm_struct *mm, pgd_t *pgd)
        free_page((unsigned long)pgd);
 }
 
+/*
+ * Used to set accessed or dirty bits in the page table entries
+ * on other architectures. On x86, the accessed and dirty bits
+ * are tracked by hardware. However, do_wp_page calls this function
+ * to also make the pte writeable at the same time the dirty bit is
+ * set. In that case we do actually need to write the PTE.
+ */
 int ptep_set_access_flags(struct vm_area_struct *vma,
                          unsigned long address, pte_t *ptep,
                          pte_t entry, int dirty)
@@ -310,7 +317,7 @@ int ptep_set_access_flags(struct vm_area_struct *vma,
        if (changed && dirty) {
                *ptep = entry;
                pte_update_defer(vma->vm_mm, address, ptep);
-               flush_tlb_page(vma, address);
+               __flush_tlb_one(address);
        }
 
        return changed;