linux-kernel - [PATCH 2/8] KVM: x86/mmu: Don't do TLB flush when zappings SPTEs in invalid roots

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Date: Wed, 10 Jan 2024 18:00:42 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	David Matlack <dmatlack@...gle.com>, Pattara Teerapong <pteerapong@...gle.com>
Subject: [PATCH 2/8] KVM: x86/mmu: Don't do TLB flush when zappings SPTEs in
 invalid roots

Don't force a TLB flush when zapping SPTEs in invalid roots as vCPUs
can't be actively using invalid roots (zapping SPTEs in invalid roots is
necessary only to ensure KVM doesn't mark a page accessed/dirty after it
is freed by the primary MMU).

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 372da098d3ce..68920877370b 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -811,7 +811,13 @@ static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root,
 			continue;
 
 		tdp_mmu_iter_set_spte(kvm, &iter, 0);
-		flush = true;
+
+		/*
+		 * Zappings SPTEs in invalid roots doesn't require a TLB flush,
+		 * see kvm_tdp_mmu_zap_invalidated_roots() for details.
+		 */
+		if (!root->role.invalid)
+			flush = true;
 	}
 
 	rcu_read_unlock();
-- 
2.43.0.275.g3460e3d667-goog