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Message-ID: <86ecc67a-8567-f3b3-02c9-572474af8e72@linux.intel.com>
Date:   Wed, 9 Aug 2023 18:51:41 +0800
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Cc:     baolu.lu@linux.intel.com,
        "iommu@lists.linux.dev" <iommu@lists.linux.dev>,
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Subject: Re: [PATCH 0/5] Share sva domains with all devices bound to a mm
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To:     "Tian, Kevin" <kevin.tian@intel.com>,
        "Zhang, Tina" <tina.zhang@intel.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Michael Shavit <mshavit@google.com>
References: <20230808074944.7825-1-tina.zhang@intel.com>
 <184044ad-880f-5452-727b-f7fd18330c22@linux.intel.com>
 <BN9PR11MB52766D5CF4F959D58E60C9238C12A@BN9PR11MB5276.namprd11.prod.outlook.com>
From:   Baolu Lu <baolu.lu@linux.intel.com>
In-Reply-To: <BN9PR11MB52766D5CF4F959D58E60C9238C12A@BN9PR11MB5276.namprd11.prod.outlook.com>
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On 2023/8/9 17:44, Tian, Kevin wrote:
>> From: Baolu Lu<baolu.lu@linux.intel.com>
>> Sent: Wednesday, August 9, 2023 8:18 AM
>>
>> 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.
>>
> iirc it's a simplification to free mm pasid at __mmdrop() otherwise the
> implementation is tricky, but I don't remember all the detail...

Yeah, probably we could also free the sva domains in __mmdrop()? Remove
the refcount for sva domain just like what we did for pasid (at the
beginning we had refcount for each pasid...).

Best regards,
baolu