Re: [PATCH v3 04/10] iommu/vt-d: Add helper to setup pasid nested translation

Baolu Lu
2023-05-26T04:17:23Z

On 5/24/23 3:16 PM, Tian, Kevin wrote:
>> From: Yi Liu <yi.l.liu@intel.com>
>> Sent: Thursday, May 11, 2023 10:51 PM
>>
>> +
>> +/**
>> + * intel_pasid_setup_nested() - Set up PASID entry for nested translation.
>> + * This could be used for guest shared virtual address. In this case, the
>> + * first level page tables are used for GVA-GPA translation in the guest,
>> + * second level page tables are used for GPA-HPA translation.
>
> it's not just for guest SVA. Actually in this series it's RID_PASID nested
> translation.

Yes.

>> + *
>> + * @iommu: IOMMU which the device belong to
>> + * @dev: Device to be set up for translation
>> + * @pasid: PASID to be programmed in the device PASID table
>> + * @domain: User domain nested on a s2 domain
>
> "User stage-1 domain"

Yes.

>> + */
>> +int intel_pasid_setup_nested(struct intel_iommu *iommu, struct device
>> *dev,
>> + u32 pasid, struct dmar_domain *domain)
>> +{
>> + struct iommu_hwpt_intel_vtd *s1_cfg = &domain->s1_cfg;
>> + pgd_t *s1_gpgd = (pgd_t *)(uintptr_t)domain->s1_pgtbl;
>> + struct dmar_domain *s2_domain = domain->s2_domain;
>> + u16 did = domain_id_iommu(domain, iommu);
>> + struct dma_pte *pgd = s2_domain->pgd;
>> + struct pasid_entry *pte;
>> + int agaw;
>> +
>> + if (!ecap_nest(iommu->ecap)) {
>> + pr_err_ratelimited("%s: No nested translation support\n",
>> + iommu->name);
>> + return -ENODEV;
>> + }
>> +
>> + /*
>> + * Sanity checking performed by caller to make sure address width
>
> "by caller"? it's checked in this function.

This comment need to be updated.

>> + * matching in two dimensions: CPU vs. IOMMU, guest vs. host.
>> + */
>> + switch (s1_cfg->addr_width) {
>> + case ADDR_WIDTH_4LEVEL:
>> + break;
>> +#ifdef CONFIG_X86
>> + case ADDR_WIDTH_5LEVEL:
>> + if (!cpu_feature_enabled(X86_FEATURE_LA57) ||
>> + !cap_fl5lp_support(iommu->cap)) {
>> + dev_err_ratelimited(dev,
>> + "5-level paging not supported\n");
>> + return -EINVAL;
>> + }
>> + break;
>> +#endif
>> + default:
>> + dev_err_ratelimited(dev, "Invalid guest address width %d\n",
>> + s1_cfg->addr_width);
>> + return -EINVAL;
>> + }
>> +
>> + if ((s1_cfg->flags & IOMMU_VTD_PGTBL_SRE) && !ecap_srs(iommu-
>>> ecap)) {
>> + pr_err_ratelimited("No supervisor request support on %s\n",
>> + iommu->name);
>> + return -EINVAL;
>> + }
>> +
>> + if ((s1_cfg->flags & IOMMU_VTD_PGTBL_EAFE)
>> && !ecap_eafs(iommu->ecap)) {
>> + pr_err_ratelimited("No extended access flag support
>> on %s\n",
>> + iommu->name);
>> + return -EINVAL;
>> + }
>> +
>> + /*
>> + * Memory type is only applicable to devices inside processor
>> coherent
>> + * domain. Will add MTS support once coherent devices are available.
>> + */
>> + if (s1_cfg->flags & IOMMU_VTD_PGTBL_MTS_MASK) {
>> + pr_warn_ratelimited("No memory type support %s\n",
>> + iommu->name);
>> + return -EINVAL;
>> + }
>
> If it's unsupported why exposing them in the uAPI at this point?

Agreed. We can remove this flag for now.

>> +
>> + agaw = iommu_skip_agaw(s2_domain, iommu, &pgd);
>> + if (agaw < 0) {
>> + dev_err_ratelimited(dev, "Invalid domain page table\n");
>> + return -EINVAL;
>> + }
>
> this looks problematic.
>
> static inline int iommu_skip_agaw(struct dmar_domain *domain,
> struct intel_iommu *iommu,
> struct dma_pte **pgd)
> {
> int agaw;
>
> for (agaw = domain->agaw; agaw > iommu->agaw; agaw--) {
> *pgd = phys_to_virt(dma_pte_addr(*pgd));
> if (!dma_pte_present(*pgd))
> return -EINVAL;
> }
>
> return agaw;
> }
>
> why is it safe to change pgd level of s2 domain when it's used as
> the parent? this s2 pgtbl might be used by other devices behind
> other iommus which already maps GPAs in a level which this
> iommu doesn't support...
>
> shouldn't we simply fail it as another incompatible condition?

You are right. We can change it to this:

if (domain->agaw > iommu->agaw)
return -EINVAL;

>
>> +
>> + /* First level PGD (in GPA) must be supported by the second level. */
>> + if ((uintptr_t)s1_gpgd > (1ULL << s2_domain->gaw)) {
>> + dev_err_ratelimited(dev,
>> + "Guest PGD %lx not supported,
>> max %llx\n",
>> + (uintptr_t)s1_gpgd, s2_domain-
>>> max_addr);
>> + return -EINVAL;
>> + }
>
> I'm not sure how useful this check is. Even if the pgd is sane the
> lower level PTEs could include unsupported GPA's. If a guest really
> doesn't want to follow the GPA restriction which vIOMMU reports,
> it can easily cause IOMMU fault in many ways.

You are right.

> Then why treating pgd specially?

I have no memory about this check for now. Yi, any thought?

Best regards,
baolu