[PATCH v6 09/11] KVM: x86: Implement fast_only versions of kvm_{test_,}age_gfn

[James Houghton]

These fast-only versions simply ignore the shadow MMU. We can locklessly
handle the shadow MMU later.

Set HAVE_KVM_MMU_NOTIFIER_YOUNG_FAST_ONLY for X86_64 only, as that is
the only case where the TDP MMU might be used. Without the TDP MMU, the
fast-only notifiers will always be no-ops. It would be ideal not to
report has_fast_only if !tdp_mmu_enabled, but tdp_mmu_enabled can be
changed at any time.

Signed-off-by: James Houghton <jthoughton at google.com>
---
 arch/x86/kvm/Kconfig   | 1 +
 arch/x86/kvm/mmu/mmu.c | 4 ++--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 6ac43074c5e9..ed9049cf1255 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_MMU_NOTIFIER_YOUNG_FAST_ONLY if X86_64
 	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 919d59385f89..3c6c9442434a 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1641,7 +1641,7 @@ 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);
 
-	if (kvm_has_shadow_mmu_sptes(kvm)) {
+	if (!range->arg.fast_only && kvm_has_shadow_mmu_sptes(kvm)) {
 		write_lock(&kvm->mmu_lock);
 		young = kvm_handle_gfn_range(kvm, range, kvm_age_rmap);
 		write_unlock(&kvm->mmu_lock);
@@ -1657,7 +1657,7 @@ 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);
 
-	if (!young && kvm_has_shadow_mmu_sptes(kvm)) {
+	if (!young && !range->arg.fast_only && kvm_has_shadow_mmu_sptes(kvm)) {
 		write_lock(&kvm->mmu_lock);
 		young = kvm_handle_gfn_range(kvm, range, kvm_test_age_rmap);
 		write_unlock(&kvm->mmu_lock);
-- 
2.46.0.rc1.232.g9752f9e123-goog