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

[Shameerali Kolothum Thodi]

Hi Eric,

First, many thanks for the respin. I will go through all of these(iommu/vfio/Qemu)
and will do a thorough verification/tests on our hardware. 

> -----Original Message-----
> From: Auger Eric [mailto:eric.auger@xxxxxxxxxx]
> Sent: 17 November 2020 08:40
> 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)
> 
> 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.

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 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.

Ok. Will verify this.

> >> - "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.

OK.

> > 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.

That’s cool. I will check this.
 
> If we clearly identify all the public dependencies needed for vSVA/ARM I
> can help you respinning on top of them

Sure. I will rebase the vSVA related changes on top of your series and then
we can take it from there. Thanks for your support.

Thanks,
Shameer

> 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
> >