Re: [PATCH] KVM: VMX: Fix NMI event loss

[Sean Christopherson]

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@xxxxxxxxxx