linux-kernel - Re: [RFC PATCH v6 04/20] iommu/arm-smmu: add capability IOMMU_CAP_INTR

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Date:	Mon, 16 Jun 2014 09:30:32 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Joerg Roedel <joro@...tes.org>
Cc:	Will Deacon <will.deacon@....com>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	Antonios Motakis <a.motakis@...tualopensystems.com>,
	"kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"tech@...tualopensystems.com" <tech@...tualopensystems.com>,
	"a.rigo@...tualopensystems.com" <a.rigo@...tualopensystems.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"kim.phillips@...escale.com" <kim.phillips@...escale.com>,
	"stuart.yoder@...escale.com" <stuart.yoder@...escale.com>,
	"eric.auger@...aro.org" <eric.auger@...aro.org>,
	"moderated list:ARM SMMU DRIVER" 
	<linux-arm-kernel@...ts.infradead.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v6 04/20] iommu/arm-smmu: add capability
 IOMMU_CAP_INTR_REMAP

On Mon, 2014-06-16 at 17:21 +0200, Joerg Roedel wrote:
> On Mon, Jun 16, 2014 at 04:13:29PM +0100, Will Deacon wrote:
> > MSIs look just like memory accesses made by the device, so the SMMU
> > will translate them to point at the GIC ITS (doorbell). The ITS then
> > has tables to work out how to route the MSI.
> > 
> > So, if IOMMU_CAP_INTR_REMAP is simply supposed to indicate that the
> > SMMU can translate MSIs to point somewhere else, then the ARM SMMU can
> > always do it.  If it's supposed to indicate that the actual MSI
> > payload can be filtered/routed, then that requires the GIC ITS.
> > 
> > The part I'm unsure of is how VFIO knows where to map the MSIs to.
> > That requires knowledge of the physical and virtual doorbell pages --
> > is that discoverable in the API?
> 
> VFIO does not care about the actual routing, it only cares that the
> device can not send interrupts it is not allowed to send (e.g.
> interrupts to vectors used by other devices or, on x86, exception vectors).
> If that is guaranteed by the SMMU or the GIC ITS hardware and driver
> then it is fine to set this flag.

Yep, I agree.  Thanks,

Alex

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