linux-kernel - Re: [PATCH] KVM: VMX: Fix NMI event loss

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Message-ID: <SY4P282MB1084112AF3101FE83300ABFF9DE0A@SY4P282MB1084.AUSP282.PROD.OUTLOOK.COM>
Date:   Mon, 28 Aug 2023 23:53:43 +0800
From:   Tianyi Liu <i.pear@...look.com>
To:     seanjc@...gle.com
Cc:     i.pear@...look.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, peterz@...radead.org
Subject: Re: [PATCH] KVM: VMX: Fix NMI event loss

On Mon, Aug 28, 2023, Sean Christopherson wrote:
> On Mon, Aug 28, 2023, Tianyi Liu wrote:
> > Hi, Sean:
> > 
> > I have found that in the latest version of the kernel, some PMU events are
> > being lost. I used bisect and found out the breaking commit [1], which
> > moved the handling of NMI events from `handle_exception_irqoff` to
> > `vmx_vcpu_enter_exit`.
> > 
> > If I revert this part as done in this patch, it works correctly. However,
> > I'm not really familiar with KVM, and I'm not sure about the intent behind
> > the original patch [1].
> 
> FWIW, the goal was to invoke vmx_do_nmi_irqoff() before leaving the "noinstr"
> region.  I messed up and forgot that vmx_get_intr_info() relied on metadata being
> reset after VM-Exit :-/
> 
> > Could you please take a look on this? Thanks a lot.
> 
> Please try this patch, it should fix the problem but I haven't fully tested it
> against an affected workload yet.  I'll do that later today.
> 
> https://lore.kernel.org/all/20230825014532.2846714-1-seanjc@google.com

This works for me, thanks.