linux-kernel - Re: [PATCH 0/5] Share sva domains with all devices bound to a mm

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Message-ID: <ZNOmsfE3Eheuelv8@ziepe.ca>
Date:   Wed, 9 Aug 2023 11:46:09 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Baolu Lu <baolu.lu@...ux.intel.com>
Cc:     Tina Zhang <tina.zhang@...el.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Michael Shavit <mshavit@...gle.com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] Share sva domains with all devices bound to a mm

On Wed, Aug 09, 2023 at 08:18:18AM +0800, Baolu Lu wrote:
> On 2023/8/8 15:49, Tina Zhang wrote:
> > A sva domain's lifetime begins with binding a device to a mm and ends
> > by releasing all the bound devices from that sva domain. Technically,
> > there could be more than one sva domain identified by the mm PASID for
> > the use of bound devices issuing DMA transactions.
> > 
> > To support mm PASID 1:n with sva domains, each mm needs to keep both a
> > reference list of allocated sva domains and the corresponding PASID.
> > However, currently, mm struct only has one pasid field for sva usage,
> > which is used to keep the info of an assigned PASID. That pasid field
> > cannot provide sufficient info to build up the 1:n mapping between PASID
> > and sva domains.
> 
> Is it more appropriate to have the same life cycle for sva domain and mm
> pasid? I feel that they represent the same thing, that is, the address
> space shared by mm to a device.

No! The iommu_domain and the PASID are totally seperate objects with
their own lifecycles.

The SVA domain should NEVER be tied to the mm enqcmd PASID.

We might decide to free all the domains and keep the PASID around (can
we even revoke the enqcmd pasid while the MM is alive?)

Jason