Re: [RFC v3 00/10] KVM PCIe/MSI passthrough on ARM/ARM64 and IOVA reserved regions

[Auger Eric]

Hi Will,

On 30/11/2016 11:37, Will Deacon wrote:
> On Wed, Nov 30, 2016 at 10:49:33AM +0100, Auger Eric wrote:
>> On 15/11/2016 14:09, Eric Auger wrote:
>>> Following LPC discussions, we now report reserved regions through
>>> iommu-group sysfs reserved_regions attribute file.
>>>
>>> Reserved regions are populated through the IOMMU get_resv_region callback
>>> (former get_dm_regions), now implemented by amd-iommu, intel-iommu and
>>> arm-smmu.
>>>
>>> The intel-iommu reports the [FEE0_0000h - FEF0_000h] MSI window as an
>>> IOMMU_RESV_NOMAP reserved region.
>>>
>>> arm-smmu reports the MSI window (arbitrarily located at 0x8000000 and
>>> 1MB large) and the PCI host bridge windows.
>>>
>>> The series integrates a not officially posted patch from Robin:
>>> "iommu/dma: Allow MSI-only cookies".
>>>
>>> This series currently does not address IRQ safety assessment.
>>
>> I will respin this series taking into account Joerg's comment. Does
>> anyone have additional comments or want to put forward some conceptual
>> issues with the current direction and with this implementation?
>>
>> As for the IRQ safety assessment, in a first step I would propose to
>> remove the IOMMU_CAP_INTR_REMAP from arm-smmus and consider the
>> assignment as unsafe. Any objection?
> 
> Well, yeah, because it's perfectly safe with GICv3.

Well except if you have an MSI controller in-between the device and the
sMMU (typically embedded in the host bridge). Detecting this situation
is not straightforward; hence my proposal.

Thanks

Eric
> 
> Will
> 
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