Date: Thu, 7 Apr 2016 11:50:01 -0600
From: Alex Williamson <alex.williamson@redhat.com>
To: Eric Auger <eric.auger@linaro.org>
Cc: eric.auger@st.com, robin.murphy@arm.com, will.deacon@arm.com,
        joro@8bytes.org, tglx@linutronix.de, jason@lakedaemon.net,
        marc.zyngier@arm.com, christoffer.dall@linaro.org,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
        kvm@vger.kernel.org, suravee.suthikulpanit@amd.com, patches@linaro.org,
        linux-kernel@vger.kernel.org, Manish.Jaggi@caviumnetworks.com,
        Bharat.Bhushan@freescale.com, pranav.sawargaonkar@gmail.com,
        p.fedin@samsung.com, iommu@lists.linux-foundation.org,
        Jean-Philippe.Brucker@arm.com, julien.grall@arm.com
Subject: Re: [PATCH v6 0/7] KVM PCIe/MSI passthrough on ARM/ARM64: kernel
 part 1/3: iommu changes
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On Thu, 7 Apr 2016 14:28:59 +0200
Eric Auger <eric.auger@linaro.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@linaro.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