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

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Message-ID: <20220125151602.GL84788@nvidia.com>
Date:   Tue, 25 Jan 2022 11:16:02 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Ben Skeggs <bskeggs@...hat.com>,
        "Raj, Ashok" <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/7] iommu cleanup and refactoring

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