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

Jason Gunthorpe
2026-01-27T15:11:45Z

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