linux-kernel - Re: [RFC v2 8/8] iommu/arm-smmu: implement add_reserved

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Date:   Fri, 11 Nov 2016 17:22:11 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Auger Eric <eric.auger@...hat.com>
Cc:     drjones@...hat.com, jason@...edaemon.net, kvm@...r.kernel.org,
        marc.zyngier@....com, punit.agrawal@....com, will.deacon@....com,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        diana.craciun@....com, alex.williamson@...hat.com,
        pranav.sawargaonkar@...il.com,
        linux-arm-kernel@...ts.infradead.org, tglx@...utronix.de,
        robin.murphy@....com, christoffer.dall@...aro.org,
        eric.auger.pro@...il.com
Subject: Re: [RFC v2 8/8] iommu/arm-smmu: implement add_reserved_regions
 callback

Hi Eric,

On Fri, Nov 11, 2016 at 04:47:01PM +0100, Auger Eric wrote:
> Effectively in passthrough use case, the userspace defines the address
> space layout and maps guest RAM PA=IOVA to PAs (using
> VFIO_IOMMU_MAP_DMA). But this address space does not comprise the MSI
> IOVAs. Userspace does not care about MSI IOMMU mapping. So the MSI IOVA
> region must be allocated by either the VFIO driver or the IOMMU driver I
> think. Who else could initialize the IOVA allocator domain?

So I think we need a way to tell userspace about the reserved regions
(per iommu-group) so that userspace knows where it can not map anything,
and VFIO can enforce that. But the right struct here is not an
iova-allocator rb-tree, a ordered linked list should be sufficient.


	Joerg