iommu/arm-smmu-v3: Use S2FWB for NESTED domains

Force Write Back (FWB) changes how the S2 IOPTE's MemAttr field
works. When S2FWB is supported and enabled the IOPTE will force cachable
access to IOMMU_CACHE memory when nesting with a S1 and deny cachable
access when !IOMMU_CACHE.

When using a single stage of translation, a simple S2 domain, it doesn't
change things for PCI devices as it is just a different encoding for the
existing mapping of the IOMMU protection flags to cachability attributes.
For non-PCI it also changes the combining rules when incoming transactions
have inconsistent attributes.

However, when used with a nested S1, FWB has the effect of preventing the
guest from choosing a MemAttr in it's S1 that would cause ordinary DMA to
bypass the cache. Consistent with KVM we wish to deny the guest the
ability to become incoherent with cached memory the hypervisor believes is
cachable so we don't have to flush it.

Allow NESTED domains to be created if the SMMU has S2FWB support and use
S2FWB for NESTING_PARENTS. This is an additional option to CANWBS.

Link: https://patch.msgid.link/r/10-v4-9e99b76f3518+3a8-smmuv3_nesting_jgg@nvidia.com
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Reviewed-by: Donald Dutile <ddutile@redhat.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

3 files changed, 15 insertions, 3 deletions

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
index 91247a2a2d2c..a1c8fcd4797c 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
@@ -220,9 +220,12 @@ struct iommufd_viommu *arm_vsmmu_alloc(struct device *dev,
 	 * Must support some way to prevent the VM from bypassing the cache
 	 * because VFIO currently does not do any cache maintenance. canwbs
 	 * indicates the device is fully coherent and no cache maintenance is
-	 * ever required, even for PCI No-Snoop.
+	 * ever required, even for PCI No-Snoop. S2FWB means the S1 can't make
+	 * things non-coherent using the memattr, but No-Snoop behavior is not
+	 * effected.
 	 */
-	if (!arm_smmu_master_canwbs(master))
+	if (!arm_smmu_master_canwbs(master) &&
+	    !(smmu->features & ARM_SMMU_FEAT_S2FWB))
 		return ERR_PTR(-EOPNOTSUPP);
 
 	vsmmu = iommufd_viommu_alloc(ictx, struct arm_vsmmu, core,
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 53f12b9d78ab..de598d66b5c2 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -1046,7 +1046,8 @@ void arm_smmu_get_ste_used(const __le64 *ent, __le64 *used_bits)
 	/* S2 translates */
 	if (cfg & BIT(1)) {
 		used_bits[1] |=
-			cpu_to_le64(STRTAB_STE_1_EATS | STRTAB_STE_1_SHCFG);
+			cpu_to_le64(STRTAB_STE_1_S2FWB | STRTAB_STE_1_EATS |
+				    STRTAB_STE_1_SHCFG);
 		used_bits[2] |=
 			cpu_to_le64(STRTAB_STE_2_S2VMID | STRTAB_STE_2_VTCR |
 				    STRTAB_STE_2_S2AA64 | STRTAB_STE_2_S2ENDI |
@@ -1654,6 +1655,8 @@ void arm_smmu_make_s2_domain_ste(struct arm_smmu_ste *target,
 		FIELD_PREP(STRTAB_STE_1_EATS,
 			   ats_enabled ? STRTAB_STE_1_EATS_TRANS : 0));
 
+	if (pgtbl_cfg->quirks & IO_PGTABLE_QUIRK_ARM_S2FWB)
+		target->data[1] |= cpu_to_le64(STRTAB_STE_1_S2FWB);
 	if (smmu->features & ARM_SMMU_FEAT_ATTR_TYPES_OVR)
 		target->data[1] |= cpu_to_le64(FIELD_PREP(STRTAB_STE_1_SHCFG,
 							  STRTAB_STE_1_SHCFG_INCOMING));
@@ -2472,6 +2475,9 @@ static int arm_smmu_domain_finalise(struct arm_smmu_domain *smmu_domain,
 		pgtbl_cfg.oas = smmu->oas;
 		fmt = ARM_64_LPAE_S2;
 		finalise_stage_fn = arm_smmu_domain_finalise_s2;
+		if ((smmu->features & ARM_SMMU_FEAT_S2FWB) &&
+		    (flags & IOMMU_HWPT_ALLOC_NEST_PARENT))
+			pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_ARM_S2FWB;
 		break;
 	default:
 		return -EINVAL;
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 3fabe187ea78..5a025d310dbe 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
@@ -58,6 +58,7 @@ struct arm_smmu_device;
 #define IDR1_SIDSIZE			GENMASK(5, 0)
 
 #define ARM_SMMU_IDR3			0xc
+#define IDR3_FWB			(1 << 8)
 #define IDR3_RIL			(1 << 10)
 
 #define ARM_SMMU_IDR5			0x14
@@ -265,6 +266,7 @@ static inline u32 arm_smmu_strtab_l2_idx(u32 sid)
 #define STRTAB_STE_1_S1COR		GENMASK_ULL(5, 4)
 #define STRTAB_STE_1_S1CSH		GENMASK_ULL(7, 6)
 
+#define STRTAB_STE_1_S2FWB		(1UL << 25)
 #define STRTAB_STE_1_S1STALLD		(1UL << 27)
 
 #define STRTAB_STE_1_EATS		GENMASK_ULL(29, 28)
@@ -740,6 +742,7 @@ struct arm_smmu_device {
 #define ARM_SMMU_FEAT_ATTR_TYPES_OVR	(1 << 20)
 #define ARM_SMMU_FEAT_HA		(1 << 21)
 #define ARM_SMMU_FEAT_HD		(1 << 22)
+#define ARM_SMMU_FEAT_S2FWB		(1 << 23)
 	u32				features;
 
 #define ARM_SMMU_OPT_SKIP_PREFETCH	(1 << 0)