linux-kernel - Re: [PATCH v2 2/3] KVM: SVM: Don't update IRTEs if APICv/AVIC is disable

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Message-ID: <CALMp9eTQovt83qgB1pM3NTYaNNRU+wrRhNA9NfsRO4RDnbVU3Q@mail.gmail.com>
Date: Thu, 20 Mar 2025 09:08:30 -0700
From: Jim Mattson <jmattson@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Yosry Ahmed <yosry.ahmed@...ux.dev>
Subject: Re: [PATCH v2 2/3] KVM: SVM: Don't update IRTEs if APICv/AVIC is disable

On Thu, Mar 20, 2025 at 7:31 AM Sean Christopherson <seanjc@...gle.com> wrote:
>
> Skip IRTE updates if AVIC is disabled/unsupported, as forcing the IRTE
> into remapped mode (kvm_vcpu_apicv_active() will never be true) is
> unnecessary and wasteful.  The IOMMU driver is responsible for putting
> IRTEs into remapped mode when an IRQ is allocated by a device, long before
> that device is assigned to a VM.  I.e. the kernel as a whole has major
> issues if the IRTE isn't already in remapped mode.
>
> Opportunsitically kvm_arch_has_irq_bypass() to query for APICv/AVIC, so
> so that all checks in KVM x86 incorporate the same information.
>
> Cc: Yosry Ahmed <yosry.ahmed@...ux.dev>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Nit: "disable" -> "disabled" in the shortlog.