iommu/arm-smmu-v3: Ensure we sync STE when only changing config field

The SMMUv3 architecture permits caching of data structures deemed to be
"reachable" by the SMU, which includes STEs marked as invalid. When
transitioning an STE to a bypass/fault configuration at init or detach
time, we mistakenly elide the CMDQ_OP_CFGI_STE operation in some cases,
therefore potentially leaving the old STE state cached in the SMMU.

This patch fixes the problem by ensuring that we perform the
CMDQ_OP_CFGI_STE operation irrespective of the validity of the previous
STE.

Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reported-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

drivers/iommu/arm-smmu-v3.c

@@ -1085,7 +1085,11 @@ static void arm_smmu_write_strtab_ent(struct arm_smmu_device *smmu, u32 sid,
 		dst[1] = cpu_to_le64(STRTAB_STE_1_SHCFG_INCOMING
 			 << STRTAB_STE_1_SHCFG_SHIFT);
 		dst[2] = 0; /* Nuke the VMID */
-		if (ste_live)
+		/*
+		 * The SMMU can perform negative caching, so we must sync
+		 * the STE regardless of whether the old value was live.
+		 */
+		if (smmu)
 			arm_smmu_sync_ste_for_sid(smmu, sid);
 		return;
 	}