RE: [PATCH v2 8/8] iommu/arm-smmu-v3: Support IOMMU_DOMAIN_NESTED

Tian, Kevin
2024-08-30T08:21:20Z

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Tuesday, August 27, 2024 11:52 PM
>
> For SMMUv3 a IOMMU_DOMAIN_NESTED is composed of a S2
> iommu_domain acting
> as the parent and a user provided STE fragment that defines the CD table
> and related data with addresses translated by the S2 iommu_domain.
>
> The kernel only permits userspace to control certain allowed bits of the
> STE that are safe for user/guest control.
>
> IOTLB maintenance is a bit subtle here, the S1 implicitly includes the S2
> translation, but there is no way of knowing which S1 entries refer to a
> range of S2.
>
> For the IOTLB we follow ARM's guidance and issue a
> CMDQ_OP_TLBI_NH_ALL to
> flush all ASIDs from the VMID after flushing the S2 on any change to the
> S2.
>
> Similarly we have to flush the entire ATC if the S2 is changed.

it's clearer to mention that ATS is not supported at this point.

> @@ -2614,7 +2687,8 @@ arm_smmu_find_master_domain(struct
> arm_smmu_domain *smmu_domain,
> list_for_each_entry(master_domain, &smmu_domain->devices,
> devices_elm) {
> if (master_domain->master == master &&
> - master_domain->ssid == ssid)
> + master_domain->ssid == ssid &&
> + master_domain->nest_parent == nest_parent)
> return master_domain;
> }

there are two nest_parent flags in master_domain and smmu_domain.
Probably duplicating?

> +static struct iommu_domain *
> +arm_smmu_domain_alloc_nesting(struct device *dev, u32 flags,
> + struct iommu_domain *parent,
> + const struct iommu_user_data *user_data)
> +{
> + struct arm_smmu_master *master = dev_iommu_priv_get(dev);
> + struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
> + struct arm_smmu_nested_domain *nested_domain;
> + struct arm_smmu_domain *smmu_parent;
> + struct iommu_hwpt_arm_smmuv3 arg;
> + unsigned int eats;
> + unsigned int cfg;
> + int ret;
> +
> + if (!(master->smmu->features & ARM_SMMU_FEAT_NESTING))
> + return ERR_PTR(-EOPNOTSUPP);
> +
> + /*
> + * Must support some way to prevent the VM from bypassing the
> cache
> + * because VFIO currently does not do any cache maintenance.
> + */
> + if (!(fwspec->flags & IOMMU_FWSPEC_PCI_RC_CANWBS) &&
> + !(master->smmu->features & ARM_SMMU_FEAT_S2FWB))
> + return ERR_PTR(-EOPNOTSUPP);

this can be saved if we guard the setting of NESTING upon them.

> +
> + ret = iommu_copy_struct_from_user(&arg, user_data,
> +
> IOMMU_HWPT_DATA_ARM_SMMUV3, ste);
> + if (ret)
> + return ERR_PTR(ret);

prefer to allocating resource after static condition checks below.

> +
> + if (flags || !(master->smmu->features &
> ARM_SMMU_FEAT_TRANS_S1))
> + return ERR_PTR(-EOPNOTSUPP);

Is it possible when NESTING is supported?

> +
> + if (!(parent->type & __IOMMU_DOMAIN_PAGING))
> + return ERR_PTR(-EINVAL);

Just check parent->nest_parent

> +
> + smmu_parent = to_smmu_domain(parent);
> + if (smmu_parent->stage != ARM_SMMU_DOMAIN_S2 ||
> + smmu_parent->smmu != master->smmu)
> + return ERR_PTR(-EINVAL);

again S2 should be implied when parent->nest_parent is true.

> +
> + /* EIO is reserved for invalid STE data. */
> + if ((arg.ste[0] & ~STRTAB_STE_0_NESTING_ALLOWED) ||
> + (arg.ste[1] & ~STRTAB_STE_1_NESTING_ALLOWED))
> + return ERR_PTR(-EIO);
> +
> + cfg = FIELD_GET(STRTAB_STE_0_CFG, le64_to_cpu(arg.ste[0]));
> + if (cfg != STRTAB_STE_0_CFG_ABORT && cfg !=
> STRTAB_STE_0_CFG_BYPASS &&
> + cfg != STRTAB_STE_0_CFG_S1_TRANS)
> + return ERR_PTR(-EIO);

If vSTE is invalid those bits can be ignored?

> +
> + eats = FIELD_GET(STRTAB_STE_1_EATS, le64_to_cpu(arg.ste[1]));
> + if (eats != STRTAB_STE_1_EATS_ABT)
> + return ERR_PTR(-EIO);
> +
> + if (cfg != STRTAB_STE_0_CFG_S1_TRANS)
> + eats = STRTAB_STE_1_EATS_ABT;

this check sounds redundant. If the last check passes then eats is
already set to _ABT.

>
> +/**
> + * struct iommu_hwpt_arm_smmuv3 - ARM SMMUv3 Context Descriptor
> Table info
> + * (IOMMU_HWPT_DATA_ARM_SMMUV3)
> + *
> + * @ste: The first two double words of the user space Stream Table Entry
> for
> + * a user stage-1 Context Descriptor Table. Must be little-endian.
> + * Allowed fields: (Refer to "5.2 Stream Table Entry" in SMMUv3 HW
> Spec)
> + * - word-0: V, Cfg, S1Fmt, S1ContextPtr, S1CDMax
> + * - word-1: S1DSS, S1CIR, S1COR, S1CSH, S1STALLD

Not sure whether EATS should be documented here or not. It's handled
but must be ZERO at this point.