Re: [PATCH v1 0/4] iommu/arm-smmu-v3: Allocate vmid per vsmmu instead of s2_parent

[Nicolin Chen]

On Wed, Mar 05, 2025 at 02:31:51PM -0400, Jason Gunthorpe wrote:
> On Wed, Mar 05, 2025 at 10:23:36AM -0800, Nicolin Chen wrote:
> > On Wed, Mar 05, 2025 at 12:54:52PM -0400, Jason Gunthorpe wrote:
> > > On Tue, Mar 04, 2025 at 09:03:59PM -0800, Nicolin Chen wrote:
> > > 
> > > > Have a pair of patches getting the functions ready for the vmid migration.
> > > > Decouple the vmid from S2 parent domains and move its allocation to vSMMU
> > > > instances. Note that a regular S2 domain (!nest_parent) has to retain the
> > > > s2_cfg and vmid for non-nesting use cases, if the SMMU HW doesn't support
> > > > stage 1. Then, an S2 invalidation has to be iterated for all the vmids in
> > > > the vSMMU list introduced in the S2 parent domain.
> > > 
> > > I was planning to also fix the S2 to be able to attach to multiple
> > > IOMMU instances at the same time as getting VMID to the viommu.. It
> > > doesn't quite make sense to me that viommu would allow multi-attach
> > > but the normal cases wouldn't. Did you find a shortcut?
> > 
> > Hmm, not quite following the question. You mean vIOMMU attaching to
> > multiple S2 domains?
> 
> I mean a normal S2 domain attaching to multiple devices on multiple
> instances.

Oh, I haven't thought about a !nest_parent S2 case.

A nest_parent case will not allow devices to attach the S2 but
always to a proxy nested S1 as we discussed previously. So, I
think the implementation could be very different?

Thanks
Nicolin