Re: [PATCH v2 06/10] iommu/arm-smmu-v3: Allocate vmid in arm_vsmmu_init

On Tue, Jan 27, 2026 at 11:11:38AM -0400, Jason Gunthorpe wrote:

On Mon, Jan 26, 2026 at 07:06:24PM -0800, Nicolin Chen wrote:

quoted

On Mon, Jan 26, 2026 at 05:16:36PM -0400, Jason Gunthorpe wrote:

quoted

On Wed, Jan 21, 2026 at 05:24:24PM -0800, Nicolin Chen wrote:

quoted

VMID owned by a vSMMU should be allocated in the viommu_init callback, as
HW like tegra241-cmdqv needs to setup VINTF with the VMID.

Even the architected SMMU needs this, the VMS (not implemented in
Linux) should all share the same VMID for the same VM.

But for standard SMMU, the allocation/sharing could happen at the
device attachment to a nested (maybe bypass proxy) domain, right?

vmid is only needed for STE (attach) and invalidation.

Or do you see some other case where vmid must be allocated during
viommu_init?

It has to be tied to the VSMMU, it doesn't matter if a single VMID is
allocated on-demand for the VSMMU or for the lifetime, it has to be a
single ID and shared across all STEs.

Attachment threads are mutexed. Any device that attaches firstly
will allocate a shareable tag and add it to the array. Any other
device will get the tag from the array and reuse it. And nothing
will change this.

It is easy to understand that lifecycle by just allocating it for the
lifetime of the VSMMU..

Yea, it makes sense for that matter.

So, perhaps:

VMID owned by a vSMMU should be allocated in the viommu_init callback for
 - a straightforward lifecycle for a VMID used by a vSMMU
 - HW like tegra241-cmdqv needs to setup VINTF with the VMID

Thanks
Nicolin