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

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Message-ID: <aXgrsJeXB3bpFQqK@Asurada-Nvidia>
Date: Mon, 26 Jan 2026 19:06:24 -0800
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: <will@...nel.org>, <robin.murphy@....com>, <joro@...tes.org>,
	<jpb@...nel.org>, <praan@...gle.com>, <miko.lenczewski@....com>,
	<linux-arm-kernel@...ts.infradead.org>, <iommu@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>, <patches@...ts.linux.dev>
Subject: Re: [PATCH v2 06/10] iommu/arm-smmu-v3: Allocate vmid in
 arm_vsmmu_init

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?

> > +void arm_vsmmu_destroy(struct iommufd_viommu *viommu)
> > +{
> > +	struct arm_vsmmu *vsmmu = container_of(viommu, struct arm_vsmmu, core);
> > +
> > +	mutex_lock(&arm_smmu_asid_lock);
> > +	ida_free(&vsmmu->smmu->vmid_map, vsmmu->vmid);
> > +	mutex_unlock(&arm_smmu_asid_lock);
> 
> Need a comment explaining where the flush is.

Ack.

> It looks like arm_smmu_iotlb_tag_free() does the free in the case of
> INV_TYPE_S2_VMID_VSMMU?
> 
> But this patch doesn't have that code yet. So maybe this should be
> merged with the next patch..

Or maybe I should re-order the sequence of the patches. I'll see
what works the best.

Thanks
Nicolin