linux-kernel - [PATCH v9 06/11] KVM: x86/mmu: Skip shadow MMU test

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Message-ID: <20250204004038.1680123-7-jthoughton@google.com>
Date: Tue,  4 Feb 2025 00:40:33 +0000
From: James Houghton <jthoughton@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: David Matlack <dmatlack@...gle.com>, David Rientjes <rientjes@...gle.com>, 
	James Houghton <jthoughton@...gle.com>, Marc Zyngier <maz@...nel.org>, 
	Oliver Upton <oliver.upton@...ux.dev>, Wei Xu <weixugc@...gle.com>, Yu Zhao <yuzhao@...gle.com>, 
	Axel Rasmussen <axelrasmussen@...gle.com>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: [PATCH v9 06/11] KVM: x86/mmu: Skip shadow MMU test_young if TDP MMU
 reports page as young

Reorder the processing of the TDP MMU versus the shadow MMU when aging
SPTEs, and skip the shadow MMU entirely in the test-only case if the TDP
MMU reports that the page is young, i.e. completely avoid taking mmu_lock
if the TDP MMU SPTE is young.  Swap the order for the test-and-age helper
as well for consistency.

Signed-off-by: James Houghton <jthoughton@...gle.com>
Acked-by: Yu Zhao <yuzhao@...gle.com>
---
 arch/x86/kvm/mmu/mmu.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 1fa0f47eb6a5..4a9de4b330d7 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1592,15 +1592,15 @@ bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	bool young = false;
 
+	if (tdp_mmu_enabled)
+		young = kvm_tdp_mmu_age_gfn_range(kvm, range);
+
 	if (kvm_memslots_have_rmaps(kvm)) {
 		write_lock(&kvm->mmu_lock);
-		young = kvm_rmap_age_gfn_range(kvm, range, false);
+		young |= kvm_rmap_age_gfn_range(kvm, range, false);
 		write_unlock(&kvm->mmu_lock);
 	}
 
-	if (tdp_mmu_enabled)
-		young |= kvm_tdp_mmu_age_gfn_range(kvm, range);
-
 	return young;
 }
 
@@ -1608,15 +1608,15 @@ bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
 	bool young = false;
 
-	if (kvm_memslots_have_rmaps(kvm)) {
+	if (tdp_mmu_enabled)
+		young = kvm_tdp_mmu_test_age_gfn(kvm, range);
+
+	if (!young && kvm_memslots_have_rmaps(kvm)) {
 		write_lock(&kvm->mmu_lock);
-		young = kvm_rmap_age_gfn_range(kvm, range, true);
+		young |= kvm_rmap_age_gfn_range(kvm, range, true);
 		write_unlock(&kvm->mmu_lock);
 	}
 
-	if (tdp_mmu_enabled)
-		young |= kvm_tdp_mmu_test_age_gfn(kvm, range);
-
 	return young;
 }
 
-- 
2.48.1.362.g079036d154-goog