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

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Message-ID: <5707B2C5.5050008@linaro.org>
Date:	Fri, 8 Apr 2016 15:31:49 +0200
From:	Eric Auger <eric.auger@...aro.org>
To:	Alex Williamson <alex.williamson@...hat.com>
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

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@...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.
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
>