Re: [PATCH RFCv1 3/3] iommu/arm-smmu-v3: Allow ATS to be always on

Nicolin Chen
2026-01-26T18:41:06Z

On Mon, Jan 26, 2026 at 01:20:20PM -0400, Jason Gunthorpe wrote:
> On Mon, Jan 26, 2026 at 12:39:50PM +0000, Will Deacon wrote:
> > > + ret = arm_smmu_alloc_cd_tables(master);
> > > + if (ret)
> > > + return ret;
> >
> > Were do you allocate the second level entry for ssid 0 if we're using
> > 2-level cd tables?
>
> I don't think we need to. The entire design here has a non-valid CD entry
> for SSID 0.

Hmm, whether we allocate a 2-level cd table would actually depend on
the "1 << cd_table->s1cdmax" v.s. CTXDESC_L2_ENTRIES, right?

If the device supports PASID and s1cdmax is large, we should prepare
a 2-level cd tables, even if only SSID0 is used at this moment since
we have to support !0 pasids via potential SVA domains.

In all Other cases, we would prepare a linear one.

Nicolin