linux-kernel - Re: [PATCH v2 12/12] iommu/vt-d: Retire struct intel

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Date: Thu, 11 Apr 2024 18:42:20 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: "Tian, Kevin" <kevin.tian@...el.com>, Jason Gunthorpe <jgg@...pe.ca>
Cc: baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 "Zhang, Tina" <tina.zhang@...el.com>, "Liu, Yi L" <yi.l.liu@...el.com>,
 "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 12/12] iommu/vt-d: Retire struct intel_svm

On 2024/4/11 16:32, Tian, Kevin wrote:
>> From: Baolu Lu<baolu.lu@...ux.intel.com>
>> Sent: Thursday, April 11, 2024 3:56 PM
>>
>> On 2024/4/10 23:49, Jason Gunthorpe wrote:
>>> On Wed, Apr 10, 2024 at 10:08:44AM +0800, Lu Baolu wrote:
>>>> @@ -4388,14 +4386,8 @@ static void
>> intel_iommu_remove_dev_pasid(struct device *dev, ioasid_t pasid)
>>>>    	WARN_ON_ONCE(!dev_pasid);
>>>>    	spin_unlock_irqrestore(&dmar_domain->lock, flags);
>>>>
>>>> -	/*
>>>> -	 * The SVA implementation needs to handle its own stuffs like the
>> mm
>>>> -	 * notification. Before consolidating that code into iommu core, let
>>>> -	 * the intel sva code handle it.
>>>> -	 */
>>>>    	if (domain->type == IOMMU_DOMAIN_SVA) {
>>>>    		cache_tag_unassign_domain(dmar_domain,
>> FLPT_DEFAULT_DID, dev, pasid);
>>>> -		intel_svm_remove_dev_pasid(domain);
>>>>    	} else {
>>>>    		did = domain_id_iommu(dmar_domain, iommu);
>>>>    		cache_tag_unassign_domain(dmar_domain, did, dev, pasid);
>>> It seems very strange that SVA has a different DID scheme, why is
>>> this? PASID and SVA should not be different at this layer.
>> The VT-d spec recommends that all SVA domains share a single domain ID.
>> The PASID is unique to each SVA domain, hence the cache tags are unique.
>> Currently, the Intel IOMMU driver assigns different domain IDs for all
>> domains except the SVA type.
>>
>> Sharing a domain ID is not specific to SVA. In general, for devices
>> under a single IOMMU, domains with unique PASIDs can share the same
>> domain ID.
>>
>> In the long term (also on my task list), we will extend the cache tag
>> code to support sharing domain IDs and remove the domain type check from
>> the main code. This will also benefit the nesting case, where user
>> domains nested on the same parent could share a domain ID.
>>
> at least above might be changed to a unified call with the helper
> accepting an iommu parameter and then finding proper did
> internally based on domain type, e.g.
> 
> cache_tag_unassign_domain(domain, iommu, dev, pasid)
> {
> 	if (domain->type == IOMMU_DOMAIN_SVA)
> 		did = FLPT_DEFAULT_DID;
> 	else
> 		did = domain_id_iommu(domain, iommu);
> 
> 	...
> }

Yeah, your code is more graceful.

Best regards,
baolu