linux-kernel - Re: [PATCH v6 0/7] KVM PCIe/MSI passthrough on ARM/ARM64: kernel part 1/3: iommu changes

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Date:	Thu, 7 Apr 2016 11:50:01 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Eric Auger <eric.auger@...aro.org>
Cc:	eric.auger@...com, robin.murphy@....com, will.deacon@....com,
	joro@...tes.org, tglx@...utronix.de, jason@...edaemon.net,
	marc.zyngier@....com, christoffer.dall@...aro.org,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
	kvm@...r.kernel.org, suravee.suthikulpanit@....com,
	patches@...aro.org, linux-kernel@...r.kernel.org,
	Manish.Jaggi@...iumnetworks.com, Bharat.Bhushan@...escale.com,
	pranav.sawargaonkar@...il.com, p.fedin@...sung.com,
	iommu@...ts.linux-foundation.org, Jean-Philippe.Brucker@....com,
	julien.grall@....com
Subject: Re: [PATCH v6 0/7] KVM PCIe/MSI passthrough on ARM/ARM64: kernel
 part 1/3: iommu changes

On Thu, 7 Apr 2016 14:28:59 +0200
Eric Auger <eric.auger@...aro.org> wrote:

> Hi Alex,
> On 04/07/2016 01:15 AM, Alex Williamson wrote:
> > On Mon,  4 Apr 2016 08:06:55 +0000
> > Eric Auger <eric.auger@...aro.org> wrote:
> >   
> >> This series introduces the dma-reserved-iommu api used to:
> >> - create/destroy an iova domain dedicated to reserved iova bindings
> >> - map/unmap physical addresses onto reserved IOVAs.
> >> - unmap and destroy all IOVA reserved bindings  
> > 
> > Why are we making the decision to have an unbalanced map vs unmap, we
> > can create individual mappings, but only unmap the whole thing and
> > start over?  That's a strange interface.  Thanks,  
> The "individual" balanced unmap also exists (iommu_put_reserved_iova)
> and this is the "normal" path. This happens on msi_domain_deactivate
> (and possibly on msi_domain_set_affinity).
> 
> I added iommu_unmap_reserved to handle the case where the userspace
> registers a reserved iova domain and fails to unregister it. In that
> case one need to handle the cleanup on kernel-side and I chose to
> implement this on vfio_iommu_type1 release. All the reserved IOMMU
> bindings get destroyed on that event.
> 
> Any advice to handle this situation?

If we want to model it similar to regular iommu domains, then
iommu_free_reserved_iova_domain() should release all the mappings and
destroy the iova domain.  Additionally, since the reserved iova domain
is just a construct on top of an iommu domain, it should be sufficient
to call iommu_domain_free() to also remove the reserved iova domain if
one exists.  Thanks,

Alex