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

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Message-ID: <20161114153149.GY2078@8bytes.org>
Date:   Mon, 14 Nov 2016 16:31:50 +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 05:45:19PM +0100, Auger Eric wrote:
> On 11/11/2016 17:22, Joerg Roedel wrote:
> > 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,

> Current plan is to expose that info through an iommu-group sysfs
> attribute, as you and Robin advised.

Great.

> > and VFIO can enforce that. But the right struct here is not an
> > iova-allocator rb-tree, a ordered linked list should be sufficient.
> I plan a linked list to store the reserved regions (P2P regions, MSI
> region, ...). get_dma_regions is called with a list local to a function
> for that. Might be needed to move that list head in the iommu_group to
> avoid calling the get_dm_regions again in the attribute show function?

You can re-use the get_dm_regions() call-back available in the iommu-ops
already. Just rename it and add a flag to it which tells the iommu-core
whether that region needs to be mapped or not.

> But to allocate the IOVAs within the MSI reserved region, I understand
> you don't want us to use the iova.c allocator, is that correct? We need
> an allocator though, even a very basic one based on bitmap or whatever.
> There potentially have several different physical MSI frame pages to map.

I don't get this, what do you need and address-allocator for?



	Joerg