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

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Date:   Mon, 24 Jan 2022 13:44:04 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     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>,
        Robin Murphy <robin.murphy@....com>,
        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 Mon, Jan 24, 2022 at 09:46:26AM +0000, Tian, Kevin wrote:
> > From: Lu Baolu <baolu.lu@...ux.intel.com>
> > Sent: Monday, January 24, 2022 3:11 PM
> > 
> > Hi,
> > 
> > The guest pasid and aux-domain related code are dead code in current
> > iommu subtree. As we have reached a consensus that all these features
> > should be based on the new iommufd framework (which is under active
> > development), the first part of this series removes and cleanups all
> > the dead code.
> > 
> > The second part of this series refactors the iommu_domain by moving all
> > domain-specific ops from iommu_ops to a new domain_ops. This makes an
> > iommu_domain self-contained and represent the abstraction of an I/O
> > translation table in the IOMMU subsystem. With different type of
> > iommu_domain providing different set of ops, it's easier to support more
> > types of I/O translation tables.
> 
> You may want to give more background on this end goal. In general there
> are four IOPT types in iommufd discussions:
> 
> 1) The one currently tracked by iommu_domain, with a map/unmap semantics
> 2) The one managed by mm and shared to iommu via sva_bind/unbind ops
> 3) The one managed by userspace and bound to iommu via iommufd (require nesting)
> 4) The one managed by KVM (e.g. EPT) and shared to iommu via a TBD interface

Yes, at least from an iommufd perspective I'd like to see one struct
for all of these types, mainly so we can have a uniform alloc, attach
and detatch flow for all io page table types. 

If we want to use the iommu_domain, or make iommu_domain a sub-class
of a new struct, can be determined as we go along.

Regardless, I think this cleanup stands on its own. Moving the ops and
purging the dead code is clearly the right thing to do.

Thanks,
Jason