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

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Message-ID: <BN9PR11MB52766D5CF4F959D58E60C9238C12A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Wed, 9 Aug 2023 09:44:11 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>,
        "Zhang, Tina" <tina.zhang@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Michael Shavit <mshavit@...gle.com>
CC:     "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 0/5] Share sva domains with all devices bound to a mm

> From: Baolu Lu <baolu.lu@...ux.intel.com>
> Sent: Wednesday, August 9, 2023 8:18 AM
> 
> 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.
> 

iirc it's a simplification to free mm pasid at __mmdrop() otherwise the
implementation is tricky, but I don't remember all the detail...