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

Sean Christopherson
2022-04-15T00:43:52Z

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@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@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)
--
2.36.0.rc0.470.gd361397f0d-goog