Commit af3511ff authored by Lai Jiangshan's avatar Lai Jiangshan Committed by Paolo Bonzini
Browse files

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: default avatarLai Jiangshan <laijs@linux.alibaba.com>

Message-Id: <20210531174628.10265-1-jiangshanlai@gmail.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent b1bd5cba

arch/x86/kvm/x86.c

+4 −2
Original line number Diff line number Diff line
@@ -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;