linux-kernel - Re: [PATCH 0/2] KVM: SVM: Set pCPU during IRTE update if vCPU is running

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Date:   Wed, 9 Aug 2023 07:23:56 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Joao Martins <joao.m.martins@...cle.com>
Cc:     Alejandro Jimenez <alejandro.j.jimenez@...cle.com>,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        "dengqiao . joey" <dengqiao.joey@...edance.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 0/2] KVM: SVM: Set pCPU during IRTE update if vCPU is running

On Wed, Aug 09, 2023, Joao Martins wrote:
> On 09/08/2023 00:31, Sean Christopherson wrote:
> > Fix a bug where KVM doesn't set the pCPU affinity for running vCPUs when
> > updating IRTE routing.  Not setting the pCPU means the IOMMU will signal
> > the wrong pCPU's doorbell until the vCPU goes through a put+load cycle.
> > 
> 
> Or also framed as an inefficiency that we depend on the GALog (for a running
> vCPU) for interrupt delivery until the put+load cycle happens. I don't think I
> ever reproduced the missed interrupt case in our stress testing.

Ah, I'll reword the changelog in patch 2 if this only delays the interrupt instead
of dropping it entirely.

> > I waffled for far too long between making this one patch or two.  Moving
> > the lock doesn't make all that much sense as a standalone patch, but in the
> > end, I decided that isolating the locking change would be useful in the
> > unlikely event that it breaks something.  If anyone feels strongly about
> > making this a single patch, I have no objection to squashing these together.
> > 
> IMHO, as two patches looks better;
> 
> For what is worth:
> 
> 	Reviewed-by: Joao Martins <joao.m.martins@...cle.com>
> 
> I think Alejandro had reported his testing as successful here:
> 
> https://lore.kernel.org/kvm/caefe41b-2736-3df9-b5cd-b81fc4c30ff0@oracle.com/
> 
> OTOH, he didn't give the Tested-by explicitly

Yeah, I almost asked for a Tested-by, but figured it would be just as easy to
post the patches.