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

[Shameerali Kolothum Thodi]

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;
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> Cc: jean-philippe@xxxxxxxxxx; alex.williamson@xxxxxxxxxx;
> jacob.jun.pan@xxxxxxxxxxxxxxx; yi.l.liu@xxxxxxxxx; peter.maydell@xxxxxxxxxx;
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> 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.
> - "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 donât think
this matters for non-vsva cases as Guest kernel table/CD(pasid 0) will never
get invalidated. 

> - "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.

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.

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