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 10:58:26 -0400
From:   Alejandro Jimenez <alejandro.j.jimenez@...cle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Joao Martins <joao.m.martins@...cle.com>
Cc:     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 8/9/23 10:23, Sean Christopherson wrote:
> 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.

Right, I was never able to see any dropped interrupts when testing the baseline host kernel with "idle=poll" on my guest.
Though I didn't reproduce Dengqiao's setup exactly e.g. they imply using isolcpus in the host kernel params.

> 
> 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.

I was hoping to find more time to test with other configs (i.e. more closely matching the original environment).
That being said, besides the positive results from the validation script mentioned earlier, I have been using the
patched kernel to launch guests in my setup for quite some time now without encountering any issues. From my side:

Tested-by: Alejandro Jimenez <alejandro.j.jimenez@...cle.com>