emulate accessed bit for EPT

Commit Message

Rik van Riel Feb. 3, 2010, 9:11 p.m. UTC

None

Patch

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 89a49fb..6101615 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -856,9 +856,15 @@  static int kvm_age_rmapp(struct kvm *kvm, unsigned long *rmapp,
 	u64 *spte;
 	int young = 0;
 
-	/* always return old for EPT */
+	/*
+	 * Emulate the accessed bit for EPT, by checking if this page has
+	 * an EPT mapping, and clearing it if it does. On the next access,
+	 * a new EPT mapping will be established.
+	 * This has some overhead, but not as much as the cost of swapping
+	 * out actively used pages or breaking up actively used hugepages.
+	 */
 	if (!shadow_accessed_mask)
-		return 0;
+		return kvm_unmap_rmapp(kvm, rmapp, data);
 
 	spte = rmap_next(kvm, rmapp, NULL);
 	while (spte) {