[PATCH v3 5/7] KVM: x86: Participate in bitmap-based PTE aging

[James Houghton]

Only handle the TDP MMU case for now. In other cases, if a bitmap was
not provided, fallback to the slowpath that takes mmu_lock, or, if a
bitmap was provided, inform the caller that the bitmap is unreliable.

Suggested-by: Yu Zhao <yuzhao at google.com>
Signed-off-by: James Houghton <jthoughton at google.com>
---
 arch/x86/include/asm/kvm_host.h | 14 ++++++++++++++
 arch/x86/kvm/mmu/mmu.c          | 16 ++++++++++++++--
 arch/x86/kvm/mmu/tdp_mmu.c      | 10 +++++++++-
 3 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 3b58e2306621..c30918d0887e 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -2324,4 +2324,18 @@ int memslot_rmap_alloc(struct kvm_memory_slot *slot, unsigned long npages);
  */
 #define KVM_EXIT_HYPERCALL_MBZ		GENMASK_ULL(31, 1)
 
+#define kvm_arch_prepare_bitmap_age kvm_arch_prepare_bitmap_age
+static inline bool kvm_arch_prepare_bitmap_age(struct mmu_notifier *mn)
+{
+	/*
+	 * Indicate that we support bitmap-based aging when using the TDP MMU
+	 * and the accessed bit is available in the TDP page tables.
+	 *
+	 * We have no other preparatory work to do here, so we do not need to
+	 * redefine kvm_arch_finish_bitmap_age().
+	 */
+	return IS_ENABLED(CONFIG_X86_64) && tdp_mmu_enabled
+					 && shadow_accessed_mask;
+}
+
 #endif /* _ASM_X86_KVM_HOST_H */
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 992e651540e8..fae1a75750bb 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1674,8 +1674,14 @@ bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	bool young = false;
 
-	if (kvm_memslots_have_rmaps(kvm))
+	if (kvm_memslots_have_rmaps(kvm)) {
+		if (range->lockless) {
+			kvm_age_set_unreliable(range);
+			return false;
+		}
+
 		young = kvm_handle_gfn_range(kvm, range, kvm_age_rmap);
+	}
 
 	if (tdp_mmu_enabled)
 		young |= kvm_tdp_mmu_age_gfn_range(kvm, range);
@@ -1687,8 +1693,14 @@ bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	bool young = false;
 
-	if (kvm_memslots_have_rmaps(kvm))
+	if (kvm_memslots_have_rmaps(kvm)) {
+		if (range->lockless) {
+			kvm_age_set_unreliable(range);
+			return false;
+		}
+
 		young = kvm_handle_gfn_range(kvm, range, kvm_test_age_rmap);
+	}
 
 	if (tdp_mmu_enabled)
 		young |= kvm_tdp_mmu_test_age_gfn(kvm, range);
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index d078157e62aa..edea01bc145f 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1217,6 +1217,9 @@ static bool age_gfn_range(struct kvm *kvm, struct tdp_iter *iter,
 	if (!is_accessed_spte(iter->old_spte))
 		return false;
 
+	if (!kvm_gfn_should_age(range, iter->gfn))
+		return false;
+
 	if (spte_ad_enabled(iter->old_spte)) {
 		iter->old_spte = tdp_mmu_clear_spte_bits(iter->sptep,
 							 iter->old_spte,
@@ -1250,7 +1253,12 @@ bool kvm_tdp_mmu_age_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
 static bool test_age_gfn(struct kvm *kvm, struct tdp_iter *iter,
 			 struct kvm_gfn_range *range)
 {
-	return is_accessed_spte(iter->old_spte);
+	bool young = is_accessed_spte(iter->old_spte);
+
+	if (young)
+		kvm_gfn_record_young(range, iter->gfn);
+
+	return young;
 }
 
 bool kvm_tdp_mmu_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
-- 
2.44.0.478.gd926399ef9-goog