Messages in this thread | | | Date | Fri, 11 Aug 2023 09:06:06 +0800 | Subject | Re: [PATCH 0/5] Share sva domains with all devices bound to a mm | From | Tina Zhang <> |
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Hi,
On 8/9/23 18:51, Baolu Lu wrote: > On 2023/8/9 17:44, Tian, Kevin wrote: >>> From: Baolu Lu<baolu.lu@linux.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... > > 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...).
For sva usage, mm->mm_count is increased in iommu_sva_domain_alloc(), and gets decreased when the domain has no users (which is checked in iommu_sva_unbind_device()).
So, in a mm's life time, there could be multiple sva domains, though they are using the same PASID. I think it makes sense to mm. Because it makes no sense to keep a sva domain alive when no users are using it, even though the mm is alive.
Regards, -Tina
> > Best regards, > baolu
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