linux-kernel - Re: [PATCH v2 2/2] iommu/vt-d: Fix NULL domain on device release

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Date: Mon, 4 Mar 2024 16:07:20 +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>, "Badger, Eric" <ebadger@...estorage.com>
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 2/2] iommu/vt-d: Fix NULL domain on device release

On 2024/3/4 15:36, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@...ux.intel.com>
>> Sent: Thursday, February 29, 2024 5:46 PM
>>
>> +
>> +/*
>> + * 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;
> 
> the spec talks about domain-selective but the code actually does
> global invalidation.

I should have included the following comments below:

/* Given that we have no idea about which domain IDs and PASIDs were
  * used in the pasid table, upgrade them to global PASID and IOTLB
  * cache invalidation. This doesn't impact the performance significantly
  * as the clearing context entry is not a critical path.
  */

> 
>> + * - Global Device-TLB invalidation to affected functions.
>> + *
>> + * Note that RWBF (Required Write-Buffer Flushing) capability has
>> + * been deprecated for scable mode. Section 11.4.2 of the VT-d spec:
>> + *
>> + * HRWBF: Hardware implementations reporting Scalable Mode Translation
>> + * Support (SMTS) as Set also report this field as Clear.
> 
> RWBF info is a bit weird given existing code doesn't touch it

Yes. I will remove above note.

> 
>> + */
>> +static void sm_context_flush_caches(struct device *dev)
>> +{
>> +	struct device_domain_info *info = dev_iommu_priv_get(dev);
>> +	struct intel_iommu *iommu = info->iommu;
>> +
>> +	iommu->flush.flush_context(iommu, 0, PCI_DEVID(info->bus, info-
>>> 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);
>> +}
>> +
>> +static void context_entry_teardown_pasid_table(struct intel_iommu
>> *iommu,
>> +					       struct context_entry *context)
>> +{
>> +	context_clear_entry(context);
>> +	if (!ecap_coherent(iommu->ecap))
>> +		clflush_cache_range(context, sizeof(*context));
> 
> this is __iommu_flush_cache(). You can use it throughout this and
> the 2nd series.

Yes.

> 
>> +
>> +void intel_pasid_teardown_sm_context(struct device *dev)
>> +{
> 
> it's clearer to call it just intel_teardown_sm_context. pasid_table
> is one field in the context entry. Having pasid leading is slightly
> confusing.

I used the intel_pasid prefix because this helper function is located in
the pasid.c file.

Best regards,
baolu