linux-kernel - Re: [PATCH v8 5/7] iommu/arm-smmu-v3: Populate smmu

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Message-ID: <20251219185605.GI254720@nvidia.com>
Date: Fri, 19 Dec 2025 14:56:05 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: will@...nel.org, jean-philippe@...aro.org, robin.murphy@....com,
	joro@...tes.org, balbirs@...dia.com, miko.lenczewski@....com,
	peterz@...radead.org, kevin.tian@...el.com, praan@...gle.com,
	linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 5/7] iommu/arm-smmu-v3: Populate smmu_domain->invs
 when attaching masters

On Fri, Dec 19, 2025 at 10:54:15AM -0800, Nicolin Chen wrote:
> On Fri, Dec 19, 2025 at 11:51:51AM -0400, Jason Gunthorpe wrote:
> > On Wed, Dec 17, 2025 at 03:24:30PM -0800, Nicolin Chen wrote:
> > > +	*cur = inv;
> > > +	switch (type) {
> > > +	case INV_TYPE_S1_ASID:
> > > +		if (master->smmu->features & ARM_SMMU_FEAT_E2H) {
> > > +			cur->size_opcode = CMDQ_OP_TLBI_EL2_VA;
> > > +			cur->nsize_opcode = CMDQ_OP_TLBI_EL2_ASID;
> > > +		} else {
> > > +			cur->size_opcode = CMDQ_OP_TLBI_NH_VA;
> > > +			cur->nsize_opcode = CMDQ_OP_TLBI_NH_ASID;
> > 
> > There is a tricky little gotcha here that probably requires a comment.
> > 
> > NH_VA and NH_ASID both take (VMID,ASID) as input since the ASID is
> > always scoped to a single VMID.
> > 
> > In this case the invalidation logic always wires the VMID to zero,
> > which is also the VMID the driver uses for S1 tables when the S2 is in
> > bypass.
> > 
> > Which is fine, we don't support an actual S1 table on top of a S2
> > table where we issue invalidations through the invs array.
> > 
> > So maybe:
> > 
> >  For S1 page tables the driver always uses VMID=0, and the
> >  invalidation logic for this type will set it as well.
> 
> Ack. And I will drop that ssid too.

It looks like the ssid is needed for ats:

@@ -3156,12 +3162,136 @@ arm_smmu_master_build_inv(struct arm_smmu_master *master,
        case INV_TYPE_ATS:
        case INV_TYPE_ATS_FULL:
                cur->size_opcode = cur->nsize_opcode = CMDQ_OP_ATC_INV;
+               cur->ssid = ssid;
                break;

Jason