Re: [PATCH v7 1/4] iommu: Generalize PASID 0 for normal DMA w/o PASID

[Jean-Philippe Brucker <jean-philippe@linaro.org>]

Hi Jacob,

On Tue, May 23, 2023 at 10:34:48AM -0700, Jacob Pan wrote:
> PCIe Process address space ID (PASID) is used to tag DMA traffic, it
> provides finer grained isolation than requester ID (RID).
> 
> For each device/RID, 0 is a special PASID for the normal DMA (no
> PASID). This is universal across all architectures that supports PASID,
> therefore warranted to be reserved globally and declared in the common
> header. Consequently, we can avoid the conflict between different PASID
> use cases in the generic code. e.g. SVA and DMA API with PASIDs.
> 
> This paved away for device drivers to choose global PASID policy while
> continue doing normal DMA.
> 
> Noting that VT-d could support none-zero RID/NO_PASID, but currently not
> used.
> 
> Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> ---
> v7:
>    - renamed IOMMU_DEF_RID_PASID to be IOMMU_NO_PASID to be more generic
> v6:
>    - let SMMU code use the common RID_PASID macro
> ---
>  .../iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c   |  2 +-
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c   | 10 ++++----
>  drivers/iommu/intel/iommu.c                   | 24 +++++++++----------
>  drivers/iommu/intel/pasid.c                   |  2 +-
>  drivers/iommu/intel/pasid.h                   |  1 -
>  include/linux/iommu.h                         |  1 +
>  6 files changed, 20 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
> index a5a63b1c947e..5e6b39881c04 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
> @@ -80,7 +80,7 @@ arm_smmu_share_asid(struct mm_struct *mm, u16 asid)
>  	 * be some overlap between use of both ASIDs, until we invalidate the
>  	 * TLB.
>  	 */
> -	arm_smmu_write_ctx_desc(smmu_domain, 0, cd);
> +	arm_smmu_write_ctx_desc(smmu_domain, IOMMU_NO_PASID, cd);
>  
>  	/* Invalidate TLB entries previously associated with that context */
>  	arm_smmu_tlb_inv_asid(smmu, asid);
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index 3fd83fb75722..6d64c8fc923f 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -1053,7 +1053,7 @@ int arm_smmu_write_ctx_desc(struct arm_smmu_domain *smmu_domain, int ssid,
>  	/*
>  	 * This function handles the following cases:
>  	 *
> -	 * (1) Install primary CD, for normal DMA traffic (SSID = 0).
> +	 * (1) Install primary CD, for normal DMA traffic (SSID = IOMMU_NO_PASID = 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.
> @@ -1869,7 +1869,7 @@ static void arm_smmu_tlb_inv_context(void *cookie)
>  		cmd.tlbi.vmid	= smmu_domain->s2_cfg.vmid;
>  		arm_smmu_cmdq_issue_cmd_with_sync(smmu, &cmd);
>  	}
> -	arm_smmu_atc_inv_domain(smmu_domain, 0, 0, 0);
> +	arm_smmu_atc_inv_domain(smmu_domain, IOMMU_NO_PASID, 0, 0);
>  }
>  
>  static void __arm_smmu_tlb_inv_range(struct arm_smmu_cmdq_ent *cmd,
> @@ -1957,7 +1957,7 @@ static void arm_smmu_tlb_inv_range_domain(unsigned long iova, size_t size,
>  	 * Unfortunately, this can't be leaf-only since we may have
>  	 * zapped an entire table.
>  	 */
> -	arm_smmu_atc_inv_domain(smmu_domain, 0, iova, size);
> +	arm_smmu_atc_inv_domain(smmu_domain, IOMMU_NO_PASID, iova, size);
>  }
>  
>  void arm_smmu_tlb_inv_range_asid(unsigned long iova, size_t size, int asid,
> @@ -2131,7 +2131,7 @@ static int arm_smmu_domain_finalise_s1(struct arm_smmu_domain *smmu_domain,
>  	 * the master has been added to the devices list for this domain.
>  	 * This isn't an issue because the STE hasn't been installed yet.
>  	 */
> -	ret = arm_smmu_write_ctx_desc(smmu_domain, 0, &cfg->cd);
> +	ret = arm_smmu_write_ctx_desc(smmu_domain, IOMMU_NO_PASID, &cfg->cd);
>  	if (ret)
>  		goto out_free_cd_tables;
>  
> @@ -2317,7 +2317,7 @@ static void arm_smmu_enable_ats(struct arm_smmu_master *master)
>  	pdev = to_pci_dev(master->dev);
>  
>  	atomic_inc(&smmu_domain->nr_ats_masters);
> -	arm_smmu_atc_inv_domain(smmu_domain, 0, 0, 0);
> +	arm_smmu_atc_inv_domain(smmu_domain, IOMMU_NO_PASID, 0, 0);
>  	if (pci_enable_ats(pdev, stu))
>  		dev_err(master->dev, "Failed to enable ATS (STU %zu)\n", stu);
>  }

Thanks, I think this makes the code clearer. For consistency you could
also add these:

---
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index 6d64c8fc923fc..c977106357961 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -1601,7 +1601,7 @@ static void arm_smmu_handle_ppr(struct arm_smmu_device *smmu, u64 *evt)

 	sid = FIELD_GET(PRIQ_0_SID, evt[0]);
 	ssv = FIELD_GET(PRIQ_0_SSID_V, evt[0]);
-	ssid = ssv ? FIELD_GET(PRIQ_0_SSID, evt[0]) : 0;
+	ssid = ssv ? FIELD_GET(PRIQ_0_SSID, evt[0]) : IOMMU_NO_PASID;
 	last = FIELD_GET(PRIQ_0_PRG_LAST, evt[0]);
 	grpid = FIELD_GET(PRIQ_1_PRG_IDX, evt[1]);

@@ -1742,7 +1742,7 @@ arm_smmu_atc_inv_to_cmd(int ssid, unsigned long iova, size_t size,
 	 */
 	*cmd = (struct arm_smmu_cmdq_ent) {
 		.opcode			= CMDQ_OP_ATC_INV,
-		.substream_valid	= !!ssid,
+		.substream_valid	= (ssid != IOMMU_NO_PASID),
 		.atc.ssid		= ssid,
 	};

@@ -1789,7 +1789,7 @@ static int arm_smmu_atc_inv_master(struct arm_smmu_master *master)
 	struct arm_smmu_cmdq_ent cmd;
 	struct arm_smmu_cmdq_batch cmds;

-	arm_smmu_atc_inv_to_cmd(0, 0, 0, &cmd);
+	arm_smmu_atc_inv_to_cmd(IOMMU_NO_PASID, 0, 0, &cmd);

 	cmds.num = 0;
 	for (i = 0; i < master->num_streams; i++) {
---

With that, for SMMU:

Reviewed-by: Jean-Philippe Brucker <jean-philippe@linaro.org>