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

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

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.

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

Jason