Re: [PATCH v4 2/9] iommu: Replace sva_iommu with iommu_attach_handle

Jason Gunthorpe
2024-04-09T23:48:02Z

On Tue, Apr 09, 2024 at 10:11:28AM +0800, Baolu Lu wrote:
> On 4/8/24 10:19 PM, Jason Gunthorpe wrote:
> > On Sat, Apr 06, 2024 at 02:09:34PM +0800, Baolu Lu wrote:
> > > On 4/3/24 7:59 PM, Jason Gunthorpe wrote:
> > > > On Wed, Apr 03, 2024 at 09:15:12AM +0800, Lu Baolu wrote:
> > > > > + /* A bond already exists, just take a reference`. */
> > > > > + handle = iommu_attach_handle_get(group, iommu_mm->pasid);
> > > > > + if (handle) {
> > > > > + mutex_unlock(&iommu_sva_lock);
> > > > > + return handle;
> > > > > }
> > > > At least in this context this is not enough we need to ensure that the
> > > > domain on the PASID is actually an SVA domain and it was installed by
> > > > this mechanism, not an iommufd domain for instance.
> > > >
> > > > ie you probably need a type field in the iommu_attach_handle to tell
> > > > what the priv is.
> > > >
> > > > Otherwise this seems like a great idea!
> > > Yes, you are right. For the SVA case, I will add the following changes.
> > > The IOMMUFD path will also need such enhancement. I will update it in
> > > the next version.
> > The only use for this is the PRI callbacks right? Maybe instead of
> > adding a handle type let's just check domain->iopf_handler ?
> >
> > Ie SVA will pass &ommu_sva_iopf_handler as its "type"
>
> Sorry that I don't fully understand the proposal here.

I was talking specifically about the type field you suggested adding
to the handle struct.

Instead of adding a type field check the domain->iopf_handler to
determine the domain and thus handle type.

> The problem is that the context code (SVA, IOMMUFD, etc.) needs to make
> sure that the attach handle is really what it has installed during
> domain attachment. The context code needs some mechanism to include some
> kind of "owner cookie" in the attach handle, so that it could check
> against it later for valid use.

Right, you have a derived struct for each user and you need a way to
check if casting from the general handle struct to the derived struct
is OK.

I'm suggesting using domain->iopf_handle as the type key.

Jason