From: Sean Christopherson <seanjc@google.com>
To: Wanpeng Li <kernellwp@gmail.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
Paolo Bonzini <pbonzini@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
stable@vger.kernel.org
Subject: Re: [PATCH 3/3] KVM: X86: Fix vCPU preempted state from guest point of view
Date: Tue, 11 May 2021 00:18:06 +0000 [thread overview]
Message-ID: <YJnNPpalqYwERwEL@google.com> (raw)
In-Reply-To: <1620466310-8428-3-git-send-email-wanpengli@tencent.com>
On Sat, May 08, 2021, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.com>
>
> Commit 66570e966dd9 (kvm: x86: only provide PV features if enabled in guest's
> CPUID) avoids to access pv tlb shootdown host side logic when this pv feature
> is not exposed to guest, however, kvm_steal_time.preempted not only leveraged
> by pv tlb shootdown logic but also mitigate the lock holder preemption issue.
> From guest point of view, vCPU is always preempted since we lose the reset of
> kvm_steal_time.preempted before vmentry if pv tlb shootdown feature is not
> exposed. This patch fixes it by clearing kvm_steal_time.preempted before
> vmentry.
>
> Fixes: 66570e966dd9 (kvm: x86: only provide PV features if enabled in guest's CPUID)
> Cc: stable@vger.kernel.org
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> arch/x86/kvm/x86.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c0244a6..c38e990 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3105,7 +3105,8 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
> st->preempted & KVM_VCPU_FLUSH_TLB);
> if (xchg(&st->preempted, 0) & KVM_VCPU_FLUSH_TLB)
> kvm_vcpu_flush_tlb_guest(vcpu);
> - }
> + } else
> + st->preempted = 0;
Curly braces needed since the if-statment needs 'em. Other than that,
Reviewed-by: Sean Christopherson <seanjc@google.com>
>
> vcpu->arch.st.preempted = 0;
>
> --
> 2.7.4
>
next prev parent reply other threads:[~2021-05-11 0:18 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-08 9:31 [PATCH 1/3] KVM: PPC: Book3S HV: exit halt polling on need_resched() as well Wanpeng Li
2021-05-08 9:31 ` [PATCH 2/3] KVM: X86: Bail out of direct yield in case of undercomitted scenarios Wanpeng Li
2021-05-11 21:44 ` Sean Christopherson
2021-05-12 2:43 ` Wanpeng Li
2021-05-12 16:59 ` Sean Christopherson
2021-05-08 9:31 ` [PATCH 3/3] KVM: X86: Fix vCPU preempted state from guest point of view Wanpeng Li
2021-05-11 0:18 ` Sean Christopherson [this message]
2021-05-11 10:28 ` Wanpeng Li
2021-05-12 0:02 ` [PATCH 1/3] KVM: PPC: Book3S HV: exit halt polling on need_resched() as well Wanpeng Li
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