Re: [PATCH v2 14/18] iommu/arm-smmu-v3: Support domains with shared CDs

From: Jason Gunthorpe <jgg@nvidia.com>
To: "Zhang, Tina" <tina.zhang@intel.com>
Cc: Michael Shavit <mshavit@google.com>,
	Will Deacon <will@kernel.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Joerg Roedel <joro@8bytes.org>,
	"jean-philippe@linaro.org" <jean-philippe@linaro.org>,
	"nicolinc@nvidia.com" <nicolinc@nvidia.com>,
	"baolu.lu@linux.intel.com" <baolu.lu@linux.intel.com>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"iommu@lists.linux.dev" <iommu@lists.linux.dev>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 14/18] iommu/arm-smmu-v3: Support domains with shared CDs
Date: Mon, 10 Jul 2023 13:55:13 -0300	[thread overview]
Message-ID: <ZKw38RrJ0FG8zbqt@nvidia.com> (raw)
In-Reply-To: <MW5PR11MB588179952AEDB50D9259549C892FA@MW5PR11MB5881.namprd11.prod.outlook.com>

On Wed, Jul 05, 2023 at 09:56:50AM +0000, Zhang, Tina wrote:

> > Possibly what we should do is conver the u32 pasid in the mm_struct to a
> > struct iommu_mm_data * and put alot more stuff in there. eg a linked list of
> > all SVA domains.

> If we are going to have 1:1 between SVA domain and pasid, why we
> need a linked list of all SVA domains? Would a SVA domain pointer be
> enough?

Kevin asked this, we can't assume that a single SVA domain is going to
work in a multi-iommu-driver system, which we are trying to enable at
the core level..

> I've got a patch-set which takes this suggestion to add an
> iommu_mm_data struct field to mm_struct. I'll send it out for review
> soon. The motivation of that patch-set is to let the
> invalidate_range() callback use the SVA domain referenced by
> mm->iommu_mm_data->sva_domain to do per-iommu IOTLB invalidation.

Huh?

You are supposed to put the struct mmu_notifier inside the sva_domain
struct and use container_of().

This is another reason why I'd prefer we de-duplicate SVA domains at
the core code level as duplicitive notifiers are expensive..

Please don't add stuff to the mm just for this reason.

Jason