Re: [PATCH v11 00/13] SMMUv3 Nested Stage Setup (IOMMU part)

[Auger Eric]

Hi Shameer,

On 5/13/20 5:57 PM, Shameerali Kolothum Thodi wrote:
> Hi Eric,
> 
>> -----Original Message-----
>> From: Auger Eric [mailto:eric.auger@xxxxxxxxxx]
>> Sent: 13 May 2020 14:29
>> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@xxxxxxxxxx>;
>> Zhangfei Gao <zhangfei.gao@xxxxxxxxxx>; eric.auger.pro@xxxxxxxxx;
>> iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
>> kvm@xxxxxxxxxxxxxxx; kvmarm@xxxxxxxxxxxxxxxxxxxxx; will@xxxxxxxxxx;
>> joro@xxxxxxxxxx; maz@xxxxxxxxxx; robin.murphy@xxxxxxx
>> Cc: jean-philippe@xxxxxxxxxx; alex.williamson@xxxxxxxxxx;
>> jacob.jun.pan@xxxxxxxxxxxxxxx; yi.l.liu@xxxxxxxxx; peter.maydell@xxxxxxxxxx;
>> tn@xxxxxxxxxxxx; bbhushan2@xxxxxxxxxxx
>> Subject: Re: [PATCH v11 00/13] SMMUv3 Nested Stage Setup (IOMMU part)
>>
> [...]
> 
>>>>> Yes that's normal this series is not meant to support vSVM at this stage.
>>>>>
>>>>> I intend to add the missing pieces during the next weeks.
>>>>
>>>> Thanks for that. I have made an attempt to add the vSVA based on
>>>> your v10 + JPBs sva patches. The host kernel and Qemu changes can
>>>> be found here[1][2].
>>>>
>>>> This basically adds multiple pasid support on top of your changes.
>>>> I have done some basic sanity testing and we have some initial success
>>>> with the zip vf dev on our D06 platform. Please note that the STALL event is
>>>> not yet supported though, but works fine if we mlock() guest usr mem.
>>>
>>> I have added STALL support for our vSVA prototype and it seems to be
>>> working(on our hardware). I have updated the kernel and qemu branches
>> with
>>> the same[1][2]. I should warn you though that these are prototype code and I
>> am pretty
>>> much re-using the VFIO_IOMMU_SET_PASID_TABLE interface for almost
>> everything.
>>> But thought of sharing, in case if it is useful somehow!.
>>
>> Thank you again for sharing the POC. I looked at the kernel and QEMU
>> branches.
>>
>> Here are some preliminary comments:
>> - "arm-smmu-v3: Reset S2TTB while switching back from nested stage":  as
>> you mentionned S2TTB reset now is featured in v11
> 
> Yes.
> 
>> - "arm-smmu-v3: Add support for multiple pasid in nested mode": I could
>> easily integrate this into my series. Update the iommu api first and
>> pass multiple CD info in a separate patch
> 
> Ok.
in v12, I added
[PATCH v12 14/15] iommu/smmuv3: Accept configs with more than one
context descriptor

I don't think you need to add s1cdmax addition as we already have
pasid_bits which should do the job.

>> - "arm-smmu-v3: Add support to Invalidate CD": CD invalidation should be
>> cascaded to host through the PASID cache invalidation uapi (no pb you
>> warned us for the POC you simply used VFIO_IOMMU_SET_PASID_TABLE). I
>> think I should add this support in my original series although it does
>> not seem to trigger any issue up to now.
> 
> Agree. Cache invalidation uapi is a better interface for this. Also I don’t think
> this matters for non-vsva cases as Guest kernel table/CD(pasid 0) will never
> get invalidated. 
in v12 I added [PATCH v12 15/15] iommu/smmuv3: Add PASID cache
invalidation per PASID. I have not tested it though.
> 
>> - "arm-smmu-v3: Remove duplication of fault propagation". I understand
>> the transcode is done somewhere else with SVA but we still need to do it
>> if a single CD is used, right? I will review the SVA code to better
>> understand.

Since I have rebase on 5.10-rc4 you will still have this duplication to
handle.
> 
> Hmm..not sure. Need to take another look to see whether we need a special
> handling for single CD or not.
> 
>> - for the STALL response injection I would tend to use a new VFIO region
>> for responses. At the moment there is a single VFIO region for reporting
>> the fault.

in v12 I added a new VFIO region to inject your fault. This was tested
with dummy event injection, this should work properly.

If we clearly identify all the public dependencies needed for vSVA/ARM I
can help you respinning on top of them

Thanks

Eric
> 
> Sure. That will be much cleaner and probably improve the context switch
> latency. Another thing I noted with STALL is that pasid_valid flag needs to be
> taken care in the SVA kernel path. 
> 
> "iommu: Remove pasid validity check for STALL model page response msg"
> Not sure this one is a proper way to handle this.
>  
>> On QEMU side:
>> - I am currently working on 3.2 range invalidation support which is
>> needed for DPDK/VFIO
>> - While at it I will look at how to incrementally introduce some of the
>> features you need in this series.
> 
> Ok. 
> 
> Thanks for taking a look at the POC.
> 
> Cheers,
> Shameer
>