linux-kernel - [PATCH 1/2] KVM: x86: allow kvm_tdp_mmu_zap_invalidated_roots with write-locked mmu

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Message-Id: <20211213112514.78552-2-pbonzini@redhat.com>
Date:   Mon, 13 Dec 2021 06:25:13 -0500
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     seanjc@...gle.com, ignat@...udflare.com, bgardon@...gle.com,
        dmatlack@...gle.com, stevensd@...omium.org,
        kernel-team@...udflare.com, stable@...r.kernel.org
Subject: [PATCH 1/2] KVM: x86: allow kvm_tdp_mmu_zap_invalidated_roots with write-locked mmu_lock

Zapping within a write-side critical section is more efficient, so it is
desirable if we know that no vCPU is running (such as within the .release
MMU notifier callback).  Prepare for reusing kvm_tdp_mmu_zap_invalidated_roots
in such scenarios.

Fixes: b7cccd397f31 ("KVM: x86/mmu: Fast invalidation for TDP MMU")
Cc: stable@...r.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/mmu/mmu.c     |  2 +-
 arch/x86/kvm/mmu/tdp_mmu.c | 17 +++++++++--------
 arch/x86/kvm/mmu/tdp_mmu.h |  2 +-
 3 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 4a3bcdd3cfe7..6fe4ab8fc0ca 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5695,7 +5695,7 @@ static void kvm_mmu_zap_all_fast(struct kvm *kvm)
 
 	if (is_tdp_mmu_enabled(kvm)) {
 		read_lock(&kvm->mmu_lock);
-		kvm_tdp_mmu_zap_invalidated_roots(kvm);
+		kvm_tdp_mmu_zap_invalidated_roots(kvm, true);
 		read_unlock(&kvm->mmu_lock);
 	}
 }
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 1db8496259ad..f2dd5c97bbc2 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -821,14 +821,18 @@ static struct kvm_mmu_page *next_invalidated_root(struct kvm *kvm,
  * only has to do a trivial amount of work. Since the roots are invalid,
  * no new SPTEs should be created under them.
  */
-void kvm_tdp_mmu_zap_invalidated_roots(struct kvm *kvm)
+void kvm_tdp_mmu_zap_invalidated_roots(struct kvm *kvm, bool shared)
 {
 	struct kvm_mmu_page *next_root;
 	struct kvm_mmu_page *root;
 	bool flush = false;
 
-	lockdep_assert_held_read(&kvm->mmu_lock);
+	kvm_lockdep_assert_mmu_lock_held(kvm, shared);
 
+	/*
+	 * rcu_read_lock is only needed for shared == true, but we
+	 * always take it for simplicity.
+	 */
 	rcu_read_lock();
 
 	root = next_invalidated_root(kvm, NULL);
@@ -838,13 +842,10 @@ void kvm_tdp_mmu_zap_invalidated_roots(struct kvm *kvm)
 
 		rcu_read_unlock();
 
-		flush = zap_gfn_range(kvm, root, 0, -1ull, true, flush, true);
+		flush = zap_gfn_range(kvm, root, 0, -1ull, true, flush, shared);
 
-		/*
-		 * Put the reference acquired in
-		 * kvm_tdp_mmu_invalidate_roots
-		 */
-		kvm_tdp_mmu_put_root(kvm, root, true);
+		/* Put the reference acquired in kvm_tdp_mmu_invalidate_roots.  */
+		kvm_tdp_mmu_put_root(kvm, root, shared);
 
 		root = next_root;
 
diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
index 3899004a5d91..24809f4ed090 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.h
+++ b/arch/x86/kvm/mmu/tdp_mmu.h
@@ -46,7 +46,7 @@ static inline bool kvm_tdp_mmu_zap_sp(struct kvm *kvm, struct kvm_mmu_page *sp)
 
 void kvm_tdp_mmu_zap_all(struct kvm *kvm);
 void kvm_tdp_mmu_invalidate_all_roots(struct kvm *kvm);
-void kvm_tdp_mmu_zap_invalidated_roots(struct kvm *kvm);
+void kvm_tdp_mmu_zap_invalidated_roots(struct kvm *kvm, bool shared);
 
 int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault);
 
-- 
2.31.1