[PATCH v2] iommu/arm-smmu-v3: Allow default substream bypass with a pasid support

[Nicolin Chen]

When an iommu_domain is set to IOMMU_DOMAIN_IDENTITY, the driver sets the
arm_smmu_domain->stage to ARM_SMMU_DOMAIN_BYPASS and skips the allocation
of a CD table, and then sets STRTAB_STE_0_CFG_BYPASS to the CONFIG field
of the STE. This works well for devices that only have one substream, i.e.
pasid disabled.

With a pasid-capable device, however, there could be a use case where it
allows an IDENTITY domain attachment without disabling its pasid feature.
This requires the driver to allocate a multi-entry CD table to attach the
IDENTITY domain to its default substream and to configure the S1DSS filed
of the STE to STRTAB_STE_1_S1DSS_BYPASS. So, there is a missing link here
between the STE setup and an IDENTITY domain attachment.

Add a new stage ARM_SMMU_DOMAIN_BYPASS_S1DSS to tag this configuration by
overriding the ARM_SMMU_DOMAIN_BYPASS if the device has pasid capability.
This new tag will allow the driver allocating a CD table yet skipping an
CD insertion from the IDENTITY domain, and setting up the STE accordingly.

In a use case of ARM_SMMU_DOMAIN_BYPASS_S1DSS, the SHCFG field of the STE
should be set to STRTAB_STE_1_SHCFG_INCOMING. In other cases of having a
CD table, the shareability comes from a CD, not the SHCFG field: according
to "13.5 Summary of attribute/permission configuration fields" in the spec
the SHCFG field value is irrelevant. So, always configure the SHCFG field
of the STE to STRTAB_STE_1_SHCFG_INCOMING when a CD table is present, for
simplification.

Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
---

Changelog
v2:
 * Rebased on top of Michael's series reworking CD table ownership:
   https://lore.kernel.org/all/20230816131925.2521220-1-mshavit@xxxxxxxxxx/
 * Added a new ARM_SMMU_DOMAIN_BYPASS_S1DSS stage to tag the use case
v1: https://lore.kernel.org/all/20230627033326.5236-1-nicolinc@xxxxxxxxxx/

 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 22 +++++++++++++++++++--
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h |  1 +
 2 files changed, 21 insertions(+), 2 deletions(-)

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 b27011b2bec9..860db4fbb995 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -1271,6 +1271,7 @@ static void arm_smmu_write_strtab_ent(struct arm_smmu_master *master, u32 sid,
 	 * 3. Update Config, sync
 	 */
 	u64 val = le64_to_cpu(dst[0]);
+	u8 s1dss = STRTAB_STE_1_S1DSS_SSID0;
 	bool ste_live = false;
 	struct arm_smmu_device *smmu = NULL;
 	struct arm_smmu_ctx_desc_cfg *cd_table = NULL;
@@ -1290,6 +1291,9 @@ static void arm_smmu_write_strtab_ent(struct arm_smmu_master *master, u32 sid,
 
 	if (smmu_domain) {
 		switch (smmu_domain->stage) {
+		case ARM_SMMU_DOMAIN_BYPASS_S1DSS:
+			s1dss = STRTAB_STE_1_S1DSS_BYPASS;
+			fallthrough;
 		case ARM_SMMU_DOMAIN_S1:
 			cd_table = &master->cd_table;
 			break;
@@ -1348,7 +1352,8 @@ static void arm_smmu_write_strtab_ent(struct arm_smmu_master *master, u32 sid,
 
 		BUG_ON(ste_live);
 		dst[1] = cpu_to_le64(
-			 FIELD_PREP(STRTAB_STE_1_S1DSS, STRTAB_STE_1_S1DSS_SSID0) |
+			 FIELD_PREP(STRTAB_STE_1_S1DSS, s1dss) |
+			 FIELD_PREP(STRTAB_STE_1_SHCFG, STRTAB_STE_1_SHCFG_INCOMING) |
 			 FIELD_PREP(STRTAB_STE_1_S1CIR, STRTAB_STE_1_S1C_CACHE_WBRA) |
 			 FIELD_PREP(STRTAB_STE_1_S1COR, STRTAB_STE_1_S1C_CACHE_WBRA) |
 			 FIELD_PREP(STRTAB_STE_1_S1CSH, ARM_SMMU_SH_ISH) |
@@ -2435,6 +2440,16 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
 	} else if (smmu_domain->smmu != smmu)
 		ret = -EINVAL;
 
+	/*
+	 * When attaching an IDENTITY domain to a master with pasid capability,
+	 * the master can still enable SVA feature by allocating a multi-entry
+	 * CD table and attaching the IDENTITY domain to its default substream
+	 * that alone can be byassed using the S1DSS field of the STE.
+	 */
+	if (smmu_domain->stage == ARM_SMMU_DOMAIN_BYPASS && master->ssid_bits &&
+	    smmu->features & ARM_SMMU_FEAT_TRANS_S1)
+		smmu_domain->stage = ARM_SMMU_DOMAIN_BYPASS_S1DSS;
+
 	mutex_unlock(&smmu_domain->init_mutex);
 	if (ret)
 		return ret;
@@ -2456,7 +2471,8 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
 	list_add(&master->domain_head, &smmu_domain->devices);
 	spin_unlock_irqrestore(&smmu_domain->devices_lock, flags);
 
-	if (smmu_domain->stage == ARM_SMMU_DOMAIN_S1) {
+	if (smmu_domain->stage == ARM_SMMU_DOMAIN_S1 ||
+	    smmu_domain->stage == ARM_SMMU_DOMAIN_BYPASS_S1DSS) {
 		if (!master->cd_table.cdtab) {
 			ret = arm_smmu_alloc_cd_tables(master);
 			if (ret) {
@@ -2464,7 +2480,9 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
 				goto out_list_del;
 			}
 		}
+	}
 
+	if (smmu_domain->stage == ARM_SMMU_DOMAIN_S1) {
 		/*
 		 * Prevent SVA from concurrently modifying the CD or writing to
 		 * the CD entry
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
index b7a91c8e9b52..e9361f85c91c 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
@@ -714,6 +714,7 @@ enum arm_smmu_domain_stage {
 	ARM_SMMU_DOMAIN_S2,
 	ARM_SMMU_DOMAIN_NESTED,
 	ARM_SMMU_DOMAIN_BYPASS,
+	ARM_SMMU_DOMAIN_BYPASS_S1DSS, /* Bypass S1 default substream only */
 };
 
 struct arm_smmu_domain {

base-commit: aed5d77d0c3d55d1949db89f27cf7a3981261ef4
-- 
2.41.0