From: Rik van Riel <riel@xxxxxxxxxx>
If ptep_set_access_flags() is invoked to upgrade access permissions
on a PTE, there is no security or data integrity reason to do a
remote TLB flush.
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@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/mm/pgtable.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)
Index: tip/arch/x86/mm/pgtable.c
===================================================================
--- tip.orig/arch/x86/mm/pgtable.c
+++ tip/arch/x86/mm/pgtable.c
@@ -306,11 +306,26 @@ int ptep_set_access_flags(struct vm_area
pte_t entry, int dirty)
{
int changed = !pte_same(*ptep, entry);
+ /*
+ * If the page used to be inaccessible (_PAGE_PROTNONE), or
+ * this call upgrades the access permissions on the same page,
+ * it is safe to skip the remote TLB flush.
+ */
+ bool flush_remote = false;
+ if (!pte_accessible(*ptep))
+ flush_remote = false;
+ else if (pte_pfn(*ptep) != pte_pfn(entry) ||
+ (pte_write(*ptep) && !pte_write(entry)) ||
+ (pte_exec(*ptep) && !pte_exec(entry)))
+ flush_remote = true;
if (changed && dirty) {
*ptep = entry;
pte_update_defer(vma->vm_mm, address, ptep);
- flush_tlb_page(vma, address);
+ if (flush_remote)
+ flush_tlb_page(vma, address);
+ else
+ __flush_tlb_one(address);
}
return changed;
--
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