x86: mm: only do a local tlb flush in ptep_set_access_flags()
The function ptep_set_access_flags() is only ever invoked to set access
flags or add write permission on a PTE. The write bit is only ever set
together with the dirty bit.
Because we only ever upgrade a PTE, 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>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Michel Lespinasse <walken@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 8573b83..be3bb46 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -301,6 +301,13 @@
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 @@
if (changed && dirty) {
*ptep = entry;
pte_update_defer(vma->vm_mm, address, ptep);
- flush_tlb_page(vma, address);
+ __flush_tlb_one(address);
}
return changed;