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

[Nicolin Chen <nicolinc@nvidia.com>]

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?

> The main issue here was to do this without degrading the invalidation
> workflow and harming SVA and DMA API performance..

I see.. The ATC_INV and TLBI_NH_ALL will be increased for the shared
S2, even if the S2 change is about a device behind one physical SMMU.

Thanks
Nicolin