linux-kernel - Re: [PATCH] KVM: SVM: Update destination when updating pi irte

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Message-ID: <3d05fcf1-dad3-826e-03e9-599ced7524b4@oracle.com>
Date:   Wed, 17 May 2023 16:32:26 +0100
From:   Joao Martins <joao.m.martins@...cle.com>
To:     "dengqiao.joey" <dengqiao.joey@...edance.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        seanjc@...gle.com, pbonzini@...hat.com
Subject: Re: [PATCH] KVM: SVM: Update destination when updating pi irte

On 17/05/2023 13:04, dengqiao.joey wrote:
> This seems to be a different issue. Joao's patch tries to fix the issue
> that IRTE is not changed. The problem I encountered is that IRTE does
> get changed, thus the destination field is also cleared by
> amd_iommu_activate_guest_mode(). 

Whether the amd_iommu_activate_guest_mode() clears the destination field or not
doesn't change the situation I think. So I don't think that is the problem
you're having. amd_iommu_activate_guest_mode() will always make IRTEs with
isRun=0. Which means your VF interrupts get injected via GALog events and the
DestID is meaningless there :/ Even if you leave the old affinity there with
isRun=1 bit it's still wrong as by the time you run the vcpu, the wrong affinity
will be used by the VF. More fundamentally I am not sure that on IRTE routing
updates in the VM that you can look on vcpu->cpu the way you are using it could
be potentially invalid when vcpus are blocked/preempted. You're changing IRTEs
in the whole VM in pi_update_irte()

My changes essentially handle the fact where IRTEs will be always updated with
the right GATag set in the IRTE ... and then when the vCPU migrates, wakes or
block+unblocks it will change IRTE[DestID] with the new pcpu (which the vcpu is
running on) via amd_iommu_update_ga(). So there's a good chance my changes fixes
your affinity issue.

	Joao