Re: [PATCH RFC v2 02/11] iommu: Add iommu_group_singleton_lockdown()

[Jason Gunthorpe]

On Mon, Apr 04, 2022 at 01:43:49PM +0800, Lu Baolu wrote:
> On 2022/3/30 19:58, Jason Gunthorpe wrote:
> > > > Testing the group size is inherently the wrong test to make.
> > > What is your suggestion then?
> > Add a flag to the group that positively indicates the group can never
> > have more than one member, even after hot plug. eg because it is
> > impossible due to ACS, or lack of bridges, and so on.
> 
> The check method seems to be bus specific. For platform devices, perhaps
> this kind of information should be retrieved from firmware interfaces
> like APCI or DT.
> 
> From this point of view, would it be simpler and more reasonable for the
> device driver to do such check? After all, it is the device driver that
> decides whether to provide SVA services to the application via uacce.

The check has to do with the interconnect, not the device - I don't
see how a device driver would know any better.

Why do you bring up uacce? Nothing should need uacce to access SVA.

Jason