linux-kernel - Re: [RFC PATCH v2 0/6] powerpc: pSeries: vfio: iommu: Re-enable support for SPAPR TCE VFIO

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Date: Fri, 10 May 2024 13:33:13 -0500
From: Shawn Anastasio <sanastasio@...torengineering.com>
To: Jason Gunthorpe <jgg@...pe.ca>, Shivaprasad G Bhat <sbhat@...ux.ibm.com>
Cc: kvm@...r.kernel.org, aik@...abs.ru, linux-kernel@...r.kernel.org,
 oohall@...il.com, ruscur@...sell.cc, brking@...ux.vnet.ibm.com,
 robh@...nel.org, svaidy@...ux.ibm.com, aneesh.kumar@...nel.org,
 joel@....id.au, naveen.n.rao@...ux.ibm.com, msuchanek@...e.de,
 jroedel@...e.de, gbatra@...ux.vnet.ibm.com, npiggin@...il.com,
 alex.williamson@...hat.com, mahesh@...ux.ibm.com,
 tpearson@...torengineering.com, Alexey Kardashevskiy <aik@....com>,
 vaibhav@...ux.ibm.com, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC PATCH v2 0/6] powerpc: pSeries: vfio: iommu: Re-enable
 support for SPAPR TCE VFIO

On 5/6/24 12:43 PM, Jason Gunthorpe wrote:
> On Sat, May 04, 2024 at 12:33:53AM +0530, Shivaprasad G Bhat wrote:
>> We have legacy workloads using VFIO in userspace/kvm guests running
>> on downstream distro kernels. We want these workloads to be able to
>> continue running on our arch.
> 
> It has been broken since 2018, I don't find this reasoning entirely
> reasonable :\
>

Raptor is currently working on an automated test runner setup to
exercise the VFIO subsystem on PowerNV and (to a lesser extent) pSeries,
so breakages like this going forward will hopefully be caught much more
quickly.

>> I firmly believe the refactoring in this patch series is a step in
>> that direction.
> 
> But fine, as long as we are going to fix it. PPC really needs this to
> be resolved to keep working.
>

Agreed. Modernizing/de-cluttering PPC's IOMMU code in general is another
task that we're working towards. As mentioned previously on the list,
we're working towards a more standard IOMMU driver for PPC that can be
used with dma_iommu, which I think will be a good step towards cleaning
this up. Initially PowerNV is going to be our target, but to the extent
that it is possible and useful, pSeries support could be brought in
later.

> Jason

Thanks,
Shawn