linux-kernel - Re: [PATCH v4 2/9] iommu: Replace sva_iommu with iommu_attach

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Message-ID: <20240409234800.GD223006@ziepe.ca>
Date: Tue, 9 Apr 2024 20:48:00 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Baolu Lu <baolu.lu@...ux.intel.com>
Cc: Kevin Tian <kevin.tian@...el.com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
	Jean-Philippe Brucker <jean-philippe@...aro.org>,
	Nicolin Chen <nicolinc@...dia.com>, Yi Liu <yi.l.liu@...el.com>,
	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	Joel Granados <j.granados@...sung.com>, iommu@...ts.linux.dev,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/9] iommu: Replace sva_iommu with iommu_attach_handle

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