Re: [PATCH 0/7] iommu cleanup and refactoring

From: Jason Gunthorpe via iommu <iommu@lists.linux-foundation.org>
To: Robin Murphy <robin.murphy@arm.com>
Cc: "Tian, Kevin" <kevin.tian@intel.com>,
	"Raj, Ashok" <ashok.raj@intel.com>,
	David Airlie <airlied@linux.ie>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	"Pan, Jacob jun" <jacob.jun.pan@intel.com>,
	Christoph Hellwig <hch@infradead.org>,
	Alex Williamson <alex.williamson@redhat.com>,
	Thierry Reding <thierry.reding@gmail.com>,
	Ben Skeggs <bskeggs@redhat.com>, Daniel Vetter <daniel@ffwll.ch>,
	Jonathan Hunter <jonathanh@nvidia.com>,
	Will Deacon <will@kernel.org>
Subject: Re: [PATCH 0/7] iommu cleanup and refactoring
Date: Tue, 25 Jan 2022 11:16:02 -0400	[thread overview]
Message-ID: <20220125151602.GL84788@nvidia.com> (raw)
In-Reply-To: <7febcba4-f5bf-6bf6-6180-895b18d1b806@arm.com>

On Tue, Jan 25, 2022 at 02:48:02PM +0000, Robin Murphy wrote:

> Agreed, certainly an IOMMU_DOMAIN_SVA type that can both encapsulate the mm
> and effectively replace iommu_sva seems like a logical and fairly small next
> step. We already have the paradigm of different domain types supporting
> different ops, so initially an SVA domain would simply allow bind/unbind
> rather than attach/detach/map/unmap.

I hope we can quickly get to a PASID enabled generic attach/detach
scheme - we really need this to do the uAPI part of this interface.

> they are fundamentally different things in their own right, and the ideal
> API should give us the orthogonality to also bind a device to an SVA domain
> without PASID (e.g. for KVM stage 2, or userspace assignment of simpler
> fault/stall-tolerant devices), or attach PASIDs to regular iommu_domains.

Yes, these are orthogonal things. A iommu driver that supports PASID
ideally should support PASID enabled attach/detatch for every
iommu_domain type it supports.

SVA should not be entangled with PASID beyond that SVA is often used
with PASID - a SVA iommu_domain should be fully usable with a RID too.

I'm hoping to see the core iommu code provide some simplified "SVA"
API that under the covers creates a SVA domain and then does a normal
PASID attach using the global PASID in the mm_struct - the
driver should not care what, or even if, PASID is used for a SVA
domain.

Jason
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