From: "Tian, Kevin" <kevin.tian@intel.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Alexey Kardashevskiy <aik@ozlabs.ru>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
Robin Murphy <robin.murphy@arm.com>,
Lu Baolu <baolu.lu@linux.intel.com>,
"Rodel, Jorg" <jroedel@suse.de>,
Alex Williamson <alex.williamson@redhat.com>,
"kvm-ppc@vger.kernel.org" <kvm-ppc@vger.kernel.org>,
Nicolin Chen <nicolinc@nvidia.com>
Subject: RE: [RFC PATCH kernel] vfio: Skip checking for IOMMU_CAP_CACHE_COHERENCY on POWER and more
Date: Thu, 07 Jul 2022 01:06:54 +0000 [thread overview]
Message-ID: <BN9PR11MB5276FB34FE0DAC75DB5D61E38C839@BN9PR11MB5276.namprd11.prod.outlook.com> (raw)
In-Reply-To: <20220705004919.GC23621@ziepe.ca>
> From: Jason Gunthorpe <jgg@ziepe.ca>
> Sent: Tuesday, July 5, 2022 8:49 AM
>
> On Fri, Jul 01, 2022 at 07:10:45AM +0000, Tian, Kevin wrote:
> > > From: Alexey Kardashevskiy <aik@ozlabs.ru>
> > > Sent: Friday, July 1, 2022 2:18 PM
> > >
> > > VFIO on POWER does not implement iommu_ops and therefore
> > > iommu_capable()
> > > always returns false and __iommu_group_alloc_blocking_domain()
> always
> > > fails.
> > >
> > > iommu_group_claim_dma_owner() in setting container fails for the same
> > > reason - it cannot allocate a domain.
> > >
> > > This skips the check for platforms supporting VFIO without implementing
> > > iommu_ops which to my best knowledge is POWER only.
> > >
> > > This also allows setting container in absence of iommu_ops.
> > >
> > > Fixes: 70693f470848 ("vfio: Set DMA ownership for VFIO devices")
> > > Fixes: e8ae0e140c05 ("vfio: Require that devices support DMA cache
> > > coherence")
> > > Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> > > ---
> > >
> > > Not quite sure what the proper small fix is and implementing iommu_ops
> > > on POWER is not going to happen any time soon or ever :-/
> >
> > I'm not sure how others feel about checking bus->iommu_ops outside
> > of iommu subsystem. This sounds a bit non-modular to me and it's not
> > obvious from the caller side why lacking of iommu_ops implies the two
> > relevant APIs are not usable.
>
> The more I think about this, the more I think POWER should implement
> partial iommu_ops to make this work. It would not support an UNMANAGED
> domain, or default domains, but it would support blocking and the
> coherency probe.
Yes, this sounds a better approach.
>
> This makes everything work properly and keeps the mess out of the core
> code.
>
> It should not be hard to do if someone can share a bit about the ppc
> code and test it..
>
> Jason
next prev parent reply other threads:[~2022-07-07 1:06 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-01 6:17 [RFC PATCH kernel] vfio: Skip checking for IOMMU_CAP_CACHE_COHERENCY on POWER and more Alexey Kardashevskiy
2022-07-01 7:10 ` Tian, Kevin
2022-07-05 0:49 ` Jason Gunthorpe
2022-07-07 1:06 ` Tian, Kevin [this message]
2022-07-01 10:34 ` Robin Murphy
2022-07-01 23:40 ` Tian, Kevin
2022-07-03 0:22 ` Jason Gunthorpe
2022-07-03 0:26 ` Jason Gunthorpe
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