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KVM: x86: Ensure PV TLB flush tracepoint reflects KVM behavior

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From: Lai Jiangshan <laijs@linux.alibaba.com>

commit af3511ff7fa2107d6410831f3d71030f5e8d2b25 upstream.

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 <laijs@linux.alibaba.com>

Message-Id: <20210531174628.10265-1-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Rishabh Bhatnagar <risbhat@amazon.com>
Tested-by: Allen Pais <apais@linux.microsoft.com>
Acked-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Rishabh Bhatnagar 2023-05-10 18:15:39 +00:00 committed by Greg Kroah-Hartman
parent 01c0002ec7
commit 4b19cbdb1d
1 changed files with 4 additions and 2 deletions
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6
arch/x86/kvm/x86.c
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@ -3041,9 +3041,11 @@ 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;