linux-kernel - Re: [PATCH] KVM: arm/arm64: vgic: add init entry to VGIC KVM device

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Message-ID: <CAFEAcA9YmAVYAOFbmV53Y3zBdcmK9MGSVR4gaLCjKxbyrZ6Xaw@mail.gmail.com>
Date:	Tue, 2 Dec 2014 17:50:00 +0000
From:	Peter Maydell <peter.maydell@...aro.org>
To:	Eric Auger <eric.auger@...aro.org>
Cc:	eric.auger@...com, Christoffer Dall <christoffer.dall@...aro.org>,
	Marc Zyngier <marc.zyngier@....com>,
	arm-mail-list <linux-arm-kernel@...ts.infradead.org>,
	"kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	kvm-devel <kvm@...r.kernel.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	Alexander Graf <agraf@...e.de>,
	"gleb@...nel.org" <gleb@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Patch Tracking <patches@...aro.org>
Subject: Re: [PATCH] KVM: arm/arm64: vgic: add init entry to VGIC KVM device

On 2 December 2014 at 17:27, Eric Auger <eric.auger@...aro.org> wrote:
> Since the advent of dynamic initialization of VGIC, this latter is
> initialized very late, on the first vcpu run. This initialization
> could be initiated much earlier by the user, as soon as it has
> provided the requested dimensioning parameters:
> - number of IRQs and number of vCPUs,
> - DIST and CPU interface base address.
>
> One motivation behind being able to initialize the VGIC sooner is
> related to the setup of IRQ injection in VFIO use case. The VFIO
> signaling, especially when used along with irqfd must be set *after*
> vgic initialization to prevent any virtual IRQ injection before
> VGIC initialization. If virtual IRQ injection occurs before the VGIC
> init, the IRQ cannot be injected and subsequent injection is blocked
> due to VFIO completion mechanism (unmask/mask or forward/unforward).

This implies that you're potentially injecting virtual IRQs
(and changing the state of the VGIC) before we actually
start running the VM (ie before userspace calls KVM_RUN).
Is that right? It seems odd, but maybe vfio works that way?

-- PMM
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