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

Nicolin Chen
2024-08-27T21:24:50Z

On Tue, Aug 27, 2024 at 12:51:38PM -0300, Jason Gunthorpe wrote:
> 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.
>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>

With some small nits:

> @@ -2192,6 +2255,16 @@ static void arm_smmu_tlb_inv_range_domain(unsigned long iova, size_t size,
> }
> __arm_smmu_tlb_inv_range(&cmd, iova, size, granule, smmu_domain);
>
> + if (smmu_domain->stage == ARM_SMMU_DOMAIN_S2 &&
> + smmu_domain->nest_parent) {

smmu_domain->nest_parent alone is enough?

[---]
> +static int arm_smmu_attach_dev_nested(struct iommu_domain *domain,
> + struct device *dev)
> +{
[..]
> + if (arm_smmu_ssids_in_use(&master->cd_table) ||

This feels more like a -EBUSY as it would be unlikely able to
attach to a different nested domain?

> + nested_domain->s2_parent->smmu != master->smmu)
> + return -EINVAL;
[---]

> +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);
> +
> + ret = iommu_copy_struct_from_user(&arg, user_data,
> + IOMMU_HWPT_DATA_ARM_SMMUV3, ste);
> + if (ret)
> + return ERR_PTR(ret);
> +
> + if (flags || !(master->smmu->features & ARM_SMMU_FEAT_TRANS_S1))
> + return ERR_PTR(-EOPNOTSUPP);

A bit redundant to the first sanity against ARM_SMMU_FEAT_NESTING,
since ARM_SMMU_FEAT_NESTING includes ARM_SMMU_FEAT_TRANS_S1.

> +
> + if (!(parent->type & __IOMMU_DOMAIN_PAGING))
> + return ERR_PTR(-EINVAL);
> +
> + smmu_parent = to_smmu_domain(parent);
> + if (smmu_parent->stage != ARM_SMMU_DOMAIN_S2 ||

Maybe "!smmu_parent->nest_parent" instead.

[---]
> + smmu_parent->smmu != master->smmu)
> + return ERR_PTR(-EINVAL);

It'd be slightly nicer if we do all the non-arg validations prior
to calling iommu_copy_struct_from_user(). Then, the following arg
validations would be closer to the copy().

> +
> + /* 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);
[---]

> /* The following are exposed for testing purposes. */
> struct arm_smmu_entry_writer_ops;
> struct arm_smmu_entry_writer {
> @@ -830,6 +849,7 @@ struct arm_smmu_master_domain {
> struct list_head devices_elm;
> struct arm_smmu_master *master;
> ioasid_t ssid;
> + u8 nest_parent;

Would it be nicer to match with the one in struct arm_smmu_domain:
+ bool nest_parent : 1;
?

> + * 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

It seems that word-1 is missing EATS.

Thanks
Nicolin