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

[Baolu Lu]

On 2023/8/9 22:46, Jason Gunthorpe wrote:
> 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.

Okay. Fair enough.

> 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?)

We ever did this and was removed to make code simple.

Best regards,
baolu