linux-kernel - Re: [PATCH v10 08/12] iommu/sva: Refactoring iommu_sva_bind/unbind

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Date:   Mon, 25 Jul 2022 18:22:06 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        Zhangfei Gao <zhangfei.gao@...aro.org>,
        "Zhu, Tony" <tony.zhu@...el.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v10 08/12] iommu/sva: Refactoring
 iommu_sva_bind/unbind_device()

On 2022/7/25 15:50, Tian, Kevin wrote:
>> From: Baolu Lu <baolu.lu@...ux.intel.com>
>> Sent: Sunday, July 24, 2022 9:48 PM
>>>
>>> The API is really refcounting the PASID:
>>>
>>>> +struct iommu_sva *iommu_sva_bind_device(struct device *dev,
>>>> +					struct mm_struct *mm);
>>>> +void iommu_sva_unbind_device(struct iommu_sva *handle);
>>>
>>> So what you need to do is store that 'iommu_sva' in the group's PASID
>>> xarray.
>>>
>>> The bind logic would be
>>>
>>>     sva = xa_load(group->pasid, mm->pasid)
>>>     if (sva)
>>>        refcount_inc(sva->users)
>>>        return sva
>>>     sva = kalloc
>>>     sva->domain = domain
>>>     xa_store(group->pasid, sva);
>>
>> Thanks for the suggestion. It makes a lot of sense to me.
>>
>> Furthermore, I'd like to separate the generic data from the caller-
>> specific things because the group->pasid_array should also be able to
>> serve other usages. Hence, the attach/detach_device_pasid interfaces
>> might be changed like below:
>>
>> /* Collection of per-pasid IOMMU data */
>> struct group_pasid {
>> 	struct iommu_domain *domain;
>> 	void *priv;
>> };
>>
> 
> Is there any reason why pasid refcnt is sva specific and needs to be
> in a priv field?

I am going to store the iommu_sva data which represents the bind
relationship between device and domain.

Best regards,
baolu