linux-kernel - [PATCH 5.17 129/146] KVM: x86: Dont re-acquire SRCU lock in complete_emulated

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Message-Id: <20220426081753.688082335@linuxfoundation.org>
Date:   Tue, 26 Apr 2022 10:22:04 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Sean Christopherson <seanjc@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.17 129/146] KVM: x86: Dont re-acquire SRCU lock in complete_emulated_io()

From: Sean Christopherson <seanjc@...gle.com>

commit 2d08935682ac5f6bfb70f7e6844ec27d4a245fa4 upstream.

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@...r.kernel.org
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
Message-Id: <20220415004343.2203171-2-seanjc@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kvm/x86.c |    7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10296,12 +10296,7 @@ static int vcpu_run(struct kvm_vcpu *vcp
 
 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)