linux-kernel - [PATCH 1/3] KVM: x86: Don't re-acquire SRCU lock in complete_emulated

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Message-Id: <20220415004343.2203171-2-seanjc@google.com>
Date:   Fri, 15 Apr 2022 00:43:41 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Anup Patel <anup@...infault.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Atish Patra <atishp@...shpatra.org>,
        David Hildenbrand <david@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, linuxppc-dev@...ts.ozlabs.org,
        kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/3] KVM: x86: Don't re-acquire SRCU lock in complete_emulated_io()

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>
---
 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)
-- 
2.36.0.rc0.470.gd361397f0d-goog