[v5,7/9] KVM: x86: Implement kvm_fast_test_age_gfn and kvm_fast_age_gfn

Commit Message

James Houghton June 11, 2024, 12:21 a.m. UTC

The fast-only notifier will only report an accurate result when the
shadow MMU is not in use.

Implement kvm_arch_young_notifier_likely_fast(), as MGLRU will check
this function to see if it should even be attempting the fast-only
notifier. We only want to attempt the notifier if there is a chance that
it will succeed (i.e., that we're using the TDP MMU).

Signed-off-by: James Houghton <[e-mail]>
---
 arch/x86/include/asm/kvm_host.h |  7 +++++
 arch/x86/kvm/Kconfig            |  1 +
 arch/x86/kvm/mmu/mmu.c          | 50 ++++++++++++++++++++++++++++++---
 3 files changed, 54 insertions(+), 4 deletions(-)

Patch

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 0dc1fa99cdbb..ca2fbc162e51 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -2338,4 +2338,11 @@  int memslot_rmap_alloc(struct kvm_memory_slot *slot, unsigned long npages);
  */
 #define KVM_EXIT_HYPERCALL_MBZ		GENMASK_ULL(31, 1)
 
+#define kvm_arch_young_notifier_likely_fast kvm_arch_young_notifier_likely_fast
+static inline bool kvm_arch_young_notifier_likely_fast(void)
+{
+	return IS_ENABLED(CONFIG_X86_64) && tdp_mmu_enabled &&
+		shadow_accessed_mask;
+}
+
 #endif /* _ASM_X86_KVM_HOST_H */
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 9dda7f8c72ed..84ae043c7d43 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -24,6 +24,7 @@  config KVM
 	select KVM_COMMON
 	select KVM_GENERIC_MMU_NOTIFIER
 	select KVM_MMU_NOTIFIER_YOUNG_LOCKLESS
+	select HAVE_KVM_YOUNG_FAST_ONLY_NOTIFIER
 	select HAVE_KVM_IRQCHIP
 	select HAVE_KVM_PFNCACHE
 	select HAVE_KVM_DIRTY_RING_TSO
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 51061f1fb3d1..ed50e78755ab 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1629,11 +1629,15 @@  static void rmap_add(struct kvm_vcpu *vcpu, const struct kvm_memory_slot *slot,
 	__rmap_add(vcpu->kvm, cache, slot, spte, gfn, access);
 }
 
-bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
+static int __kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range,
+			 bool fast_only)
 {
 	bool young = false;
 
 	if (kvm_memslots_have_rmaps(kvm)) {
+		if (fast_only)
+			return -1;
+
 		write_lock(&kvm->mmu_lock);
 		young = kvm_handle_gfn_range(kvm, range, kvm_age_rmap);
 		write_unlock(&kvm->mmu_lock);
@@ -1642,14 +1646,18 @@  bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 	if (tdp_mmu_enabled)
 		young |= kvm_tdp_mmu_age_gfn_range(kvm, range);
 
-	return young;
+	return (int)young;
 }
 
-bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
+static int __kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range,
+			      bool fast_only)
 {
 	bool young = false;
 
 	if (kvm_memslots_have_rmaps(kvm)) {
+		if (fast_only)
+			return -1;
+
 		write_lock(&kvm->mmu_lock);
 		young = kvm_handle_gfn_range(kvm, range, kvm_test_age_rmap);
 		write_unlock(&kvm->mmu_lock);
@@ -1658,7 +1666,41 @@  bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 	if (tdp_mmu_enabled)
 		young |= kvm_tdp_mmu_test_age_gfn(kvm, range);
 
-	return young;
+	return (int)young;
+}
+
+bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
+{
+	return __kvm_age_gfn(kvm, range, false);
+}
+
+bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
+{
+	return __kvm_test_age_gfn(kvm, range, false);
+}
+
+bool kvm_fast_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
+{
+	int ret = __kvm_age_gfn(kvm, range, true);
+
+	if (ret < 0) {
+		*range->arg.failed = true;
+		return false;
+	}
+
+	return ret != 0;
+}
+
+bool kvm_fast_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
+{
+	int ret = __kvm_test_age_gfn(kvm, range, true);
+
+	if (ret < 0) {
+		*range->arg.failed = true;
+		return false;
+	}
+
+	return ret != 0;
 }
 
 static void kvm_mmu_check_sptes_at_free(struct kvm_mmu_page *sp)