Subject: Re: [PATCH v6 0/7] KVM PCIe/MSI passthrough on ARM/ARM64: kernel part
 1/3: iommu changes
To: Alex Williamson <alex.williamson@redhat.com>
References: <1459757222-2668-1-git-send-email-eric.auger@linaro.org>
 <20160406171534.794c6824@t450s.home> <5706528B.2010906@linaro.org>
 <20160407115001.25de7d1e@t450s.home>
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
From: Eric Auger <eric.auger@linaro.org>
Message-ID: <5707B2C5.5050008@linaro.org>
Date: Fri, 8 Apr 2016 15:31:49 +0200
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Hi Alex,
On 04/07/2016 07:50 PM, Alex Williamson wrote:
> 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.
Yes this sounds obvious now.
  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,
Yes. For dma cookie (iommu_put_dma_cookie) I see this is done from the
iommu driver domain_free callback.

Thanks

Eric
> 
> Alex
>