From: Rishabh Bhatnagar <risbhat@amazon.com>
To: <stable@vger.kernel.org>
Cc: <gregkh@linuxfoundation.org>, <surajjs@amazon.com>,
<mbacco@amazon.com>, Lai Jiangshan <laijs@linux.alibaba.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Rishabh Bhatnagar <risbhat@amazon.com>
Subject: [PATCH 1/9] KVM: x86: Ensure PV TLB flush tracepoint reflects KVM behavior
Date: Fri, 9 Sep 2022 18:13:43 +0000 [thread overview]
Message-ID: <20220909181351.23983-2-risbhat@amazon.com> (raw)
In-Reply-To: <20220909181351.23983-1-risbhat@amazon.com>
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>
---
arch/x86/kvm/x86.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c5a08ec348e6..3640b298c42e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3032,9 +3032,11 @@ 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;
--
2.37.1
next prev parent reply other threads:[~2022-09-09 18:14 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-09 18:13 [PATCH 0/9] KVM backports to 5.10 Rishabh Bhatnagar
2022-09-09 18:13 ` Rishabh Bhatnagar [this message]
2022-09-09 18:13 ` [PATCH 2/9] KVM: x86: Fix recording of guest steal time / preempted status Rishabh Bhatnagar
2022-09-09 18:13 ` [PATCH 3/9] KVM: Fix steal time asm constraints Rishabh Bhatnagar
2022-09-09 18:13 ` [PATCH 4/9] KVM: x86: Remove obsolete disabling of page faults in kvm_arch_vcpu_put() Rishabh Bhatnagar
2022-09-09 18:13 ` [PATCH 5/9] KVM: x86: do not set st->preempted when going back to user space Rishabh Bhatnagar
2022-09-09 18:13 ` [PATCH 6/9] KVM: x86: do not report a vCPU as preempted outside instruction boundaries Rishabh Bhatnagar
2022-09-09 18:13 ` [PATCH 7/9] KVM: x86: revalidate steal time cache if MSR value changes Rishabh Bhatnagar
2022-09-09 18:13 ` [PATCH 8/9] KVM: x86: do not report preemption if the steal time cache is stale Rishabh Bhatnagar
2022-09-09 18:13 ` [PATCH 9/9] KVM: x86: move guest_pv_has out of user_access section Rishabh Bhatnagar
2022-09-09 18:26 ` [PATCH 0/9] KVM backports to 5.10 Greg KH
-- strict thread matches above, loose matches on Subject: below --
2022-09-09 18:55 Rishabh Bhatnagar
2022-09-09 18:55 ` [PATCH 1/9] KVM: x86: Ensure PV TLB flush tracepoint reflects KVM behavior Rishabh Bhatnagar
2023-05-10 18:15 [PATCH 0/9] KVM backports to 5.10 Rishabh Bhatnagar
2023-05-10 18:15 ` [PATCH 1/9] KVM: x86: Ensure PV TLB flush tracepoint reflects KVM behavior Rishabh Bhatnagar
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