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

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Date:   Wed, 30 Nov 2016 15:08:17 +0100
From:   Auger Eric <eric.auger@...hat.com>
To:     Will Deacon <will.deacon@....com>
Cc:     drjones@...hat.com, jason@...edaemon.net, kvm@...r.kernel.org,
        marc.zyngier@....com, joro@...tes.org, punit.agrawal@....com,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        diana.craciun@....com, alex.williamson@...hat.com,
        pranav.sawargaonkar@...il.com,
        linux-arm-kernel@...ts.infradead.org, tglx@...utronix.de,
        robin.murphy@....com, christoffer.dall@...aro.org,
        eric.auger.pro@...il.com
Subject: Re: [RFC v3 00/10] KVM PCIe/MSI passthrough on ARM/ARM64 and IOVA
 reserved regions

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
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> 

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