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

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Message-ID: <ZOypc+LeHdE5u0MC@google.com>
Date:   Mon, 28 Aug 2023 07:04:35 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Tianyi Liu <i.pear@...look.com>
Cc:     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, 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