Re: [PATCH v2 1/6] iommu/vt-d: Setup scalable mode context entry in probe path

Baolu Lu
2023-12-09T07:57:29Z

On 12/8/23 4:50 PM, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@linux.intel.com>
>> Sent: Tuesday, December 5, 2023 9:22 AM
>>
>> @@ -304,6 +304,11 @@ int intel_pasid_setup_first_level(struct intel_iommu
>> *iommu,
>> return -EINVAL;
>> }
>>
>> + if (intel_pasid_setup_sm_context(dev, true)) {
>> + dev_err(dev, "Context entry is not configured\n");
>> + return -ENODEV;
>> + }
>> +
>> spin_lock(&iommu->lock);
>> pte = intel_pasid_get_entry(dev, pasid);
>> if (!pte) {
>> @@ -384,6 +389,11 @@ int intel_pasid_setup_second_level(struct
>> intel_iommu *iommu,
>> return -EINVAL;
>> }
>>
>> + if (intel_pasid_setup_sm_context(dev, true)) {
>> + dev_err(dev, "Context entry is not configured\n");
>> + return -ENODEV;
>> + }
>> +
>> pgd = domain->pgd;
>> agaw = iommu_skip_agaw(domain, iommu, &pgd);
>> if (agaw < 0) {
>> @@ -505,6 +515,11 @@ int intel_pasid_setup_pass_through(struct
>> intel_iommu *iommu,
>> u16 did = FLPT_DEFAULT_DID;
>> struct pasid_entry *pte;
>>
>> + if (intel_pasid_setup_sm_context(dev, true)) {
>> + dev_err(dev, "Context entry is not configured\n");
>> + return -ENODEV;
>> + }
>> +
>> spin_lock(&iommu->lock);
>> pte = intel_pasid_get_entry(dev, pasid);
>> if (!pte) {
>
> instead of replicating the invocation in all three stubs it's simpler to
> do once in dmar_domain_attach_device() for all of them.

It's not good to repeat the code. Perhaps we can add this check to
intel_pasid_get_entry()? The rule is that you can't get the pasid entry
if the context is copied.

> Then put the deferred check outside of intel_pasid_setup_sm_context()
> instead of using a Boolean flag

Okay, that's more readable.

>> @@ -623,6 +638,11 @@ int intel_pasid_setup_nested(struct intel_iommu
>> *iommu, struct device *dev,
>> return -EINVAL;
>> }
>>
>> + if (intel_pasid_setup_sm_context(dev, true)) {
>> + dev_err_ratelimited(dev, "Context entry is not configured\n");
>> + return -ENODEV;
>> + }
>> +
>
> Do we support nested in kdump?

No.

>
>> +
>> + /*
>> + * Cache invalidation for changes to a scalable-mode context table
>> + * entry.
>> + *
>> + * Section 6.5.3.3 of the VT-d spec:
>> + * - Device-selective context-cache invalidation;
>> + * - Domain-selective PASID-cache invalidation to affected domains
>> + * (can be skipped if all PASID entries were not-present);
>> + * - Domain-selective IOTLB invalidation to affected domains;
>> + * - Global Device-TLB invalidation to affected functions.
>> + *
>> + * For kdump cases, old valid entries may be cached due to the
>> + * in-flight DMA and copied pgtable, but there is no unmapping
>> + * behaviour for them, thus we need explicit cache flushes for all
>> + * affected domain IDs and PASIDs used in the copied PASID table.
>> + * Given that we have no idea about which domain IDs and PASIDs
>> were
>> + * used in the copied tables, upgrade them to global PASID and IOTLB
>> + * cache invalidation.
>> + *
>> + * For kdump case, at this point, the device is supposed to finish
>> + * reset at its driver probe stage, so no in-flight DMA will exist,
>> + * and we don't need to worry anymore hereafter.
>> + */
>> + if (context_copied(iommu, bus, devfn)) {
>> + context_clear_entry(context);
>> + clear_context_copied(iommu, bus, devfn);
>> + iommu->flush.flush_context(iommu, 0,
>> + (((u16)bus) << 8) | devfn,
>> + DMA_CCMD_MASK_NOBIT,
>> + DMA_CCMD_DEVICE_INVL);
>> + qi_flush_pasid_cache(iommu, 0, QI_PC_GLOBAL, 0);
>> + iommu->flush.flush_iotlb(iommu, 0, 0, 0,
>> DMA_TLB_GLOBAL_FLUSH);
>> + devtlb_invalidation_with_pasid(iommu, dev,
>> IOMMU_NO_PASID);
>> + }
>
> I don't see this logic from existing code. If it's a bug fix then
> please send it separately first.

This code originates from domain_context_mapping_one(). It's not a bug
fix.

>> +
>> + context_entry_set_pasid_table(context, dev);
>
> and here is additional change to the context entry. Why is the
> context cache invalidated in the start?

The previous context entry may be copied from a previous kernel.
Therefore, we need to tear down the entry and flush the caches before
reusing it.

>
>> +
>> +static int pci_pasid_table_setup(struct pci_dev *pdev, u16 alias, void *data)
>> +{
>> + struct device *dev = data;
>> +
>> + if (dev != &pdev->dev)
>> + return 0;
>
> what is it for? the existing domain_context_mapping_cb() doesn't have
> this check then implying a behavior change.

Emm, I should remove this line and keep it consistent with the exiting
code.

Best regards,
baolu