[PATCH 1/3] KVM: x86: Don't re-acquire SRCU lock in complete_emulated_io()

Sean Christopherson seanjc at google.com
Thu Apr 14 17:43:41 PDT 2022

Don't re-acquire SRCU in complete_emulated_io() now that KVM acquires the
lock in kvm_arch_vcpu_ioctl_run().  More importantly, don't overwrite
vcpu->srcu_idx.  If the index acquired by complete_emulated_io() differs
from the one acquired by kvm_arch_vcpu_ioctl_run(), KVM will effectively
leak a lock and hang if/when synchronize_srcu() is invoked for the
relevant grace period.

Fixes: 8d25b7beca7e ("KVM: x86: pull kvm->srcu read-side to kvm_arch_vcpu_ioctl_run")
Cc: stable at vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc at google.com>
 arch/x86/kvm/x86.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ab336f7c82e4..f35fe09de59d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10450,12 +10450,7 @@ static int vcpu_run(struct kvm_vcpu *vcpu)
 static inline int complete_emulated_io(struct kvm_vcpu *vcpu)
-	int r;
-	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
-	r = kvm_emulate_instruction(vcpu, EMULTYPE_NO_DECODE);
-	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
-	return r;
+	return kvm_emulate_instruction(vcpu, EMULTYPE_NO_DECODE);
 static int complete_emulated_pio(struct kvm_vcpu *vcpu)

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