linux-kernel - Re: [PATCH 2/2] KVM: x86: check_nested_events if there is an injectable NMI

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Date:   Thu, 23 Apr 2020 17:10:45 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Cathy Avery <cavery@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        vkuznets@...hat.com, wei.huang2@....com
Subject: Re: [PATCH 2/2] KVM: x86: check_nested_events if there is an
 injectable NMI

On 23/04/20 16:42, Sean Christopherson wrote:
> On Tue, Apr 14, 2020 at 04:11:07PM -0400, Cathy Avery wrote:
>> With NMI intercept moved to check_nested_events there is a race
>> condition where vcpu->arch.nmi_pending is set late causing
> How is nmi_pending set late?  The KVM_{G,S}ET_VCPU_EVENTS paths can't set
> it because the current KVM_RUN thread holds the mutex, and the only other
> call to process_nmi() is in the request path of vcpu_enter_guest, which has
> already executed.
> 

I think the actual cause is priority inversion between NMI and
interrupts, because NMI is added last in patch 1.

Paolo