Re: [PATCH v5 0/5] cover-letter: Simplify vfio_iommu_type1 attach/detach routine

From: Nicolin Chen <nicolinc@nvidia.com>
To: <joro@8bytes.org>, Alex Williamson <alex.williamson@redhat.com>
Cc: <will@kernel.org>, <marcan@marcan.st>, <sven@svenpeter.dev>,
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Subject: Re: [PATCH v5 0/5] cover-letter: Simplify vfio_iommu_type1 attach/detach routine
Date: Wed, 13 Jul 2022 16:57:32 -0700	[thread overview]
Message-ID: <Ys9b7GSImp/sHair@Asurada-Nvidia> (raw)
In-Reply-To: <20220706120325.4741ff34.alex.williamson@redhat.com>

On Wed, Jul 06, 2022 at 12:03:25PM -0600, Alex Williamson wrote:

> On Wed, 6 Jul 2022 10:53:52 -0700
> Nicolin Chen <nicolinc@nvidia.com> wrote:
> 
> > On Wed, Jul 06, 2022 at 11:42:17AM -0600, Alex Williamson wrote:
> >
> > > On Fri, 1 Jul 2022 14:44:50 -0700
> > > Nicolin Chen <nicolinc@nvidia.com> wrote:
> > >
> > > > This is a preparatory series for IOMMUFD v2 patches. It enforces error
> > > > code -EMEDIUMTYPE in iommu_attach_device() and iommu_attach_group() when
> > > > an IOMMU domain and a device/group are incompatible. It also drops the
> > > > useless domain->ops check since it won't fail in current environment.
> > > >
> > > > These allow VFIO iommu code to simplify its group attachment routine, by
> > > > avoiding the extra IOMMU domain allocations and attach/detach sequences
> > > > of the old code.
> > > >
> > > > Worths mentioning the exact match for enforce_cache_coherency is removed
> > > > with this series, since there's very less value in doing that as KVM will
> > > > not be able to take advantage of it -- this just wastes domain memory.
> > > > Instead, we rely on Intel IOMMU driver taking care of that internally.
> > > >
> > > > This is on github:
> > > > https://github.com/nicolinc/iommufd/commits/vfio_iommu_attach
> > >
> > > How do you foresee this going in, I'm imagining Joerg would merge the
> > > first patch via the IOMMU tree and provide a topic branch that I'd
> > > merge into the vfio tree along with the remaining patches.  Sound
> > > right?  Thanks,
> >
> > We don't have any build dependency between the IOMMU change and
> > VFIO changes, yet, without the IOMMU one, any iommu_attach_group()
> > failure now would be a hard failure without a chance falling back
> > to a new_domain, which is slightly different from the current flow.
> >
> > For a potential existing use case that relies on reusing existing
> > domain, I think it'd be safer to have Joerg acking the first change
> > so you merge them all? Thank!
> 
> Works for me, I'll look for buy-in + ack from Joerg.  Thanks,
> 
> Alex

Joerg, would it be possible for you to ack at the IOMMU patch?

Thanks!
Nic