From af3511ff7fa2107d6410831f3d71030f5e8d2b25 Mon Sep 17 00:00:00 2001 From: Lai Jiangshan Date: Tue, 1 Jun 2021 01:46:28 +0800 Subject: KVM: x86: Ensure PV TLB flush tracepoint reflects KVM behavior In record_steal_time(), st->preempted is read twice, and trace_kvm_pv_tlb_flush() might output result inconsistent if kvm_vcpu_flush_tlb_guest() see a different st->preempted later. It is a very trivial problem and hardly has actual harm and can be avoided by reseting and reading st->preempted in atomic way via xchg(). Signed-off-by: Lai Jiangshan Message-Id: <20210531174628.10265-1-jiangshanlai@gmail.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/x86.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'arch/x86') diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 1cd6d4685932..e2144eedaf79 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3101,9 +3101,11 @@ static void record_steal_time(struct kvm_vcpu *vcpu) * expensive IPIs. */ if (guest_pv_has(vcpu, KVM_FEATURE_PV_TLB_FLUSH)) { + u8 st_preempted = xchg(&st->preempted, 0); + trace_kvm_pv_tlb_flush(vcpu->vcpu_id, - st->preempted & KVM_VCPU_FLUSH_TLB); - if (xchg(&st->preempted, 0) & KVM_VCPU_FLUSH_TLB) + st_preempted & KVM_VCPU_FLUSH_TLB); + if (st_preempted & KVM_VCPU_FLUSH_TLB) kvm_vcpu_flush_tlb_guest(vcpu); } else { st->preempted = 0; -- cgit v1.2.3