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

[Baolu Lu]

On 2023/8/9 17:44, Tian, Kevin wrote:
> > From: Baolu Lu<baolu.lu@xxxxxxxxxxxxxxx>
> > 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...

Yeah, probably we could also free the sva domains in __mmdrop()? Remove
the refcount for sva domain just like what we did for pasid (at the
beginning we had refcount for each pasid...).

Best regards,
baolu