Re: [PATCH 4/8] iommu/arm-smmu-v3: Add support for Substream IDs

Will Deacon
2019-06-26T18:00:34Z

On Mon, Jun 10, 2019 at 07:47:10PM +0100, Jean-Philippe Brucker wrote:
> At the moment, the SMMUv3 driver implements only one stage-1 or stage-2
> page directory per device. However SMMUv3 allows more than one address
> space for some devices, by providing multiple stage-1 page directories. In
> addition to the Stream ID (SID), that identifies a device, we can now have
> Substream IDs (SSID) identifying an address space. In PCIe, SID is called
> Requester ID (RID) and SSID is called Process Address-Space ID (PASID).
>
> Prepare the driver for SSID support, by adding context descriptor tables
> in STEs (previously a single static context descriptor). A complete
> stage-1 walk is now performed like this by the SMMU:
>
> Stream tables Ctx. tables Page tables
> +--------+ ,------->+-------+ ,------->+-------+
> : : | : : | : :
> +--------+ | +-------+ | +-------+
> SID->| STE |---' SSID->| CD |---' IOVA->| PTE |--> IPA
> +--------+ +-------+ +-------+
> : : : : : :
> +--------+ +-------+ +-------+
>
> Implement a single level of context descriptor table for now, but as with
> stream and page tables, an SSID can be split to index multiple levels of
> tables.
>
> In all stream table entries, we set S1DSS=SSID0 mode, making translations
> without an SSID use context descriptor 0. Although it would be possible by
> setting S1DSS=BYPASS, we don't currently support SSID when user selects
> iommu.passthrough.

I don't understand your comment here: iommu.passthrough works just as it did
before, right, since we set bypass in the STE config field so S1DSS is not
relevant? I also notice that SSID0 causes transactions with SSID==0 to
abort. Is a PASID of 0 reserved, so this doesn't matter?

> @@ -1062,33 +1143,90 @@ static u64 arm_smmu_cpu_tcr_to_cd(u64 tcr)
> return val;
> }
>
> -static void arm_smmu_write_ctx_desc(struct arm_smmu_device *smmu,
> - struct arm_smmu_s1_cfg *cfg)
> +static int arm_smmu_write_ctx_desc(struct arm_smmu_domain *smmu_domain,
> + int ssid, struct arm_smmu_ctx_desc *cd)
> {
> u64 val;
> + bool cd_live;
> + struct arm_smmu_device *smmu = smmu_domain->smmu;
> + __le64 *cdptr = arm_smmu_get_cd_ptr(&smmu_domain->s1_cfg, ssid);
>
> /*
> - * We don't need to issue any invalidation here, as we'll invalidate
> - * the STE when installing the new entry anyway.
> + * This function handles the following cases:
> + *
> + * (1) Install primary CD, for normal DMA traffic (SSID = 0).
> + * (2) Install a secondary CD, for SID+SSID traffic.
> + * (3) Update ASID of a CD. Atomically write the first 64 bits of the
> + * CD, then invalidate the old entry and mappings.
> + * (4) Remove a secondary CD.
> */
> - val = arm_smmu_cpu_tcr_to_cd(cfg->cd.tcr) |
> +
> + if (!cdptr)
> + return -ENOMEM;
> +
> + val = le64_to_cpu(cdptr[0]);
> + cd_live = !!(val & CTXDESC_CD_0_V);
> +
> + if (!cd) { /* (4) */
> + cdptr[0] = 0;

Should we be using WRITE_ONCE here? (although I notice we don't seem to
bother for STEs either...)

Will