linux-kernel - Re: [PATCH 0/5] Share sva domains with all devices bound to a mm

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Date:   Thu, 10 Aug 2023 09:23:23 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     baolu.lu@...ux.intel.com, Tina Zhang <tina.zhang@...el.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Michael Shavit <mshavit@...gle.com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] Share sva domains with all devices bound to a mm

On 2023/8/9 22:46, Jason Gunthorpe wrote:
> On Wed, Aug 09, 2023 at 08:18:18AM +0800, Baolu Lu wrote:
>> On 2023/8/8 15:49, Tina Zhang wrote:
>>> A sva domain's lifetime begins with binding a device to a mm and ends
>>> by releasing all the bound devices from that sva domain. Technically,
>>> there could be more than one sva domain identified by the mm PASID for
>>> the use of bound devices issuing DMA transactions.
>>>
>>> To support mm PASID 1:n with sva domains, each mm needs to keep both a
>>> reference list of allocated sva domains and the corresponding PASID.
>>> However, currently, mm struct only has one pasid field for sva usage,
>>> which is used to keep the info of an assigned PASID. That pasid field
>>> cannot provide sufficient info to build up the 1:n mapping between PASID
>>> and sva domains.
>> Is it more appropriate to have the same life cycle for sva domain and mm
>> pasid? I feel that they represent the same thing, that is, the address
>> space shared by mm to a device.
> No! The iommu_domain and the PASID are totally seperate objects with
> their own lifecycles.
> 
> The SVA domain should NEVER be tied to the mm enqcmd PASID.

Okay. Fair enough.

> 
> We might decide to free all the domains and keep the PASID around (can
> we even revoke the enqcmd pasid while the MM is alive?)

We ever did this and was removed to make code simple.

Best regards,
baolu