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

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Message-ID: <0008adc6-57fd-4ac8-8e8e-5a966596ad61@linux.intel.com>
Date:   Sat, 9 Dec 2023 15:52:44 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jason Gunthorpe <jgg@...pe.ca>
Cc:     baolu.lu@...ux.intel.com,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/6] iommu/vt-d: Setup scalable mode context entry in
 probe path

On 12/8/23 4:50 PM, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@...ux.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