[PATCH v4 07/13] iommu/arm-smmu-v3: Keep track of attached ssids

[Michael Shavit]

> And since we have a group of subdomains that are simply indexed
> by ssids, perhaps we can add an xarray to store a subdomain ptr
> along with an ssid, replacing the list?

Hmmmm, I think the only place where we search through the list for a
specific SSID is during remove_dev_pasid. We mostly use the list to
iterate over  all the masters/ssids that this domain is attached to.
I'm not sure if moving to an xarray to optimize the remove_dev_pasid
call is worth it (at the cost of iterations which IIUC would become N
log(N))