linux-kernel - [PATCH 2/5] KVM: Clear vcpu->run->flags at start of KVM

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Message-ID: <20250111012450.1262638-3-seanjc@google.com>
Date: Fri, 10 Jan 2025 17:24:47 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>, 
	Oliver Upton <oliver.upton@...ux.dev>, Michael Ellerman <mpe@...erman.id.au>, 
	Sean Christopherson <seanjc@...gle.com>
Cc: kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	kvmarm@...ts.linux.dev, linuxppc-dev@...ts.ozlabs.org, 
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/5] KVM: Clear vcpu->run->flags at start of KVM_RUN for all architectures

Clear kvm_run.flags at the start of KVM_RUN for all architectures to
minimize the probability of leaving a stale flag set.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/arm64/kvm/arm.c         | 1 -
 arch/arm64/kvm/handle_exit.c | 2 +-
 arch/powerpc/kvm/book3s_hv.c | 4 +---
 arch/x86/kvm/x86.c           | 1 -
 virt/kvm/kvm_main.c          | 3 +++
 5 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index a102c3aebdbc..925fa010bb7b 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1128,7 +1128,6 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 
 	ret = 1;
 	run->exit_reason = KVM_EXIT_UNKNOWN;
-	run->flags = 0;
 	while (ret > 0) {
 		/*
 		 * Check conditions before entering the guest
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index d7c2990e7c9e..63692c254a07 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -186,7 +186,7 @@ static int kvm_handle_guest_debug(struct kvm_vcpu *vcpu)
 	run->exit_reason = KVM_EXIT_DEBUG;
 	run->debug.arch.hsr = lower_32_bits(esr);
 	run->debug.arch.hsr_high = upper_32_bits(esr);
-	run->flags = KVM_DEBUG_ARCH_HSR_HIGH_VALID;
+	run->flags |= KVM_DEBUG_ARCH_HSR_HIGH_VALID;
 
 	switch (ESR_ELx_EC(esr)) {
 	case ESR_ELx_EC_WATCHPT_LOW:
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 25429905ae90..b253f7372774 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1704,9 +1704,7 @@ static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu,
 		/* Exit to guest with KVM_EXIT_NMI as exit reason */
 		run->exit_reason = KVM_EXIT_NMI;
 		run->hw.hardware_exit_reason = vcpu->arch.trap;
-		/* Clear out the old NMI status from run->flags */
-		run->flags &= ~KVM_RUN_PPC_NMI_DISP_MASK;
-		/* Now set the NMI status */
+		/* Note, run->flags is cleared at the start of KVM_RUN. */
 		if (vcpu->arch.mce_evt.disposition == MCE_DISPOSITION_RECOVERED)
 			run->flags |= KVM_RUN_PPC_NMI_DISP_FULLY_RECOV;
 		else
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1b04092ec76a..a8aa12e0911d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11465,7 +11465,6 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 
 	vcpu_load(vcpu);
 	kvm_sigset_activate(vcpu);
-	kvm_run->flags = 0;
 	kvm_load_guest_fpu(vcpu);
 
 	kvm_vcpu_srcu_read_lock(vcpu);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index de2c11dae231..7d2076439081 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4336,6 +4336,9 @@ static long kvm_vcpu_ioctl(struct file *filp,
 
 			put_pid(oldpid);
 		}
+
+		vcpu->run->flags = 0;
+
 		vcpu->wants_to_run = !READ_ONCE(vcpu->run->immediate_exit__unsafe);
 		r = kvm_arch_vcpu_ioctl_run(vcpu);
 		vcpu->wants_to_run = false;
-- 
2.47.1.613.gc27f4b7a9f-goog