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

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Message-ID: <9e323c4668e94ea89beec3689376b893@huawei.com>
Date:   Wed, 13 May 2020 15:57:58 +0000
From:   Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>
To:     Auger Eric <eric.auger@...hat.com>,
        Zhangfei Gao <zhangfei.gao@...aro.org>,
        "eric.auger.pro@...il.com" <eric.auger.pro@...il.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
        "will@...nel.org" <will@...nel.org>,
        "joro@...tes.org" <joro@...tes.org>,
        "maz@...nel.org" <maz@...nel.org>,
        "robin.murphy@....com" <robin.murphy@....com>
CC:     "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>,
        "yi.l.liu@...el.com" <yi.l.liu@...el.com>,
        "peter.maydell@...aro.org" <peter.maydell@...aro.org>,
        "tn@...ihalf.com" <tn@...ihalf.com>,
        "bbhushan2@...vell.com" <bbhushan2@...vell.com>
Subject: RE: [PATCH v11 00/13] SMMUv3 Nested Stage Setup (IOMMU part)

Hi Eric,

> -----Original Message-----
> From: Auger Eric [mailto:eric.auger@...hat.com]
> Sent: 13 May 2020 14:29
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>;
> Zhangfei Gao <zhangfei.gao@...aro.org>; eric.auger.pro@...il.com;
> iommu@...ts.linux-foundation.org; linux-kernel@...r.kernel.org;
> kvm@...r.kernel.org; kvmarm@...ts.cs.columbia.edu; will@...nel.org;
> joro@...tes.org; maz@...nel.org; robin.murphy@....com
> Cc: jean-philippe@...aro.org; alex.williamson@...hat.com;
> jacob.jun.pan@...ux.intel.com; yi.l.liu@...el.com; peter.maydell@...aro.org;
> tn@...ihalf.com; bbhushan2@...vell.com
> 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 don’t 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