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Reply-To: Sean Christopherson <seanjc@google.com>
Date: Tue, 21 May 2024 18:40:13 -0700
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Subject: [PATCH v2 6/6] KVM: x86: Drop now-superflous setting of
 l1tf_flush_l1d in vcpu_run()
From: Sean Christopherson <seanjc@google.com>
To: Marc Zyngier <maz@kernel.org>, Oliver Upton <oliver.upton@linux.dev>, 
	Tianrui Zhao <zhaotianrui@loongson.cn>, Bibo Mao <maobibo@loongson.cn>, 
	Huacai Chen <chenhuacai@kernel.org>, Michael Ellerman <mpe@ellerman.id.au>, 
	Anup Patel <anup@brainfault.org>, Paul Walmsley <paul.walmsley@sifive.com>, 
	Palmer Dabbelt <palmer@dabbelt.com>, Albert Ou <aou@eecs.berkeley.edu>, 
	Christian Borntraeger <borntraeger@linux.ibm.com>, Janosch Frank <frankja@linux.ibm.com>, 
	Claudio Imbrenda <imbrenda@linux.ibm.com>, Sean Christopherson <seanjc@google.com>, 
	Paolo Bonzini <pbonzini@redhat.com>
Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, 
	kvm@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, 
	linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, 
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"

Now that KVM unconditionally sets l1tf_flush_l1d in kvm_arch_vcpu_load(),
drop the redundant store from vcpu_run().  The flag is cleared only when
VM-Enter is imminent, deep below vcpu_run(), i.e. barring a KVM bug, it's
impossible for l1tf_flush_l1d to be cleared between loading the vCPU and
calling vcpu_run().

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/vmx.c | 7 ++++---
 arch/x86/kvm/x86.c     | 1 -
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index da2f95385a12..552b6a9887a5 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6672,9 +6672,10 @@ static noinstr void vmx_l1d_flush(struct kvm_vcpu *vcpu)
 		bool flush_l1d;
 
 		/*
-		 * Clear the per-vcpu flush bit, it gets set again
-		 * either from vcpu_run() or from one of the unsafe
-		 * VMEXIT handlers.
+		 * Clear the per-vcpu flush bit, it gets set again if the vCPU
+		 * is reloaded, i.e. if the vCPU is scheduled out or if KVM
+		 * exits to userspace, or if KVM reaches one of the unsafe
+		 * VMEXIT handlers, e.g. if KVM calls into the emulator.
 		 */
 		flush_l1d = vcpu->arch.l1tf_flush_l1d;
 		vcpu->arch.l1tf_flush_l1d = false;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 60fea297f91f..86ae7392cc59 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11264,7 +11264,6 @@ static int vcpu_run(struct kvm_vcpu *vcpu)
 	int r;
 
 	vcpu->run->exit_reason = KVM_EXIT_UNKNOWN;
-	vcpu->arch.l1tf_flush_l1d = true;
 
 	for (;;) {
 		/*
-- 
2.45.0.215.g3402c0e53f-goog