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Date:   Sat, 7 May 2022 16:32:58 +0800
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Subject: Re: [PATCH v5 04/12] iommu/sva: Basic data structures for SVA
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From:   Baolu Lu <baolu.lu@linux.intel.com>
To:     Jean-Philippe Brucker <jean-philippe@linaro.org>
Cc:     Kevin Tian <kevin.tian@intel.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Robin Murphy <robin.murphy@arm.com>,
        iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
        Christoph Hellwig <hch@infradead.org>,
        Jean-Philippe Brucker <jean-philippe@linaro.com>,
        Vinod Koul <vkoul@kernel.org>,
        Jacob jun Pan <jacob.jun.pan@intel.com>,
        Jason Gunthorpe <jgg@nvidia.com>, Will Deacon <will@kernel.org>
References: <20220502014842.991097-1-baolu.lu@linux.intel.com>
 <20220502014842.991097-5-baolu.lu@linux.intel.com> <YnFv0ps0Ad8v+7uH@myrica>
 <d490e542-140c-58c3-bb11-9990795272b1@linux.intel.com>
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Hi Jean,

On 2022/5/5 14:42, Baolu Lu wrote:
> On 2022/5/4 02:09, Jean-Philippe Brucker wrote:
>> On Mon, May 02, 2022 at 09:48:34AM +0800, Lu Baolu wrote:
>>> Use below data structures for SVA implementation in the IOMMU core:
>>>
>>> - struct iommu_sva_ioas
>>>    Represent the I/O address space shared with an application CPU 
>>> address
>>>    space. This structure has a 1:1 relationship with an mm_struct. It
>>>    grabs a "mm->mm_count" refcount during creation and drop it on 
>>> release.
>>
>> Do we actually need this structure?  At the moment it only keeps track of
>> bonds, which we can move to struct dev_iommu. Replacing it by a mm 
>> pointer
>> in struct iommu_domain simplifies the driver and seems to work
> 
> Fair enough.
> 
> +struct iommu_sva_ioas {
> +    struct mm_struct *mm;
> +    ioasid_t pasid;
> +
> +    /* Counter of domains attached to this ioas. */
> +    refcount_t users;
> +
> +    /* All bindings are linked here. */
> +    struct list_head bonds;
> +};
> 
> By moving @mm to struct iommu_domain and @bonds to struct dev_iommu, the
> code looks simpler. The mm, sva domain and per-device dev_iommu are
> guaranteed to be valid during bind() and unbind().
> 
> Will head this direction in the next version.

I'm trying to implement this idea in real code. It seems that we need
additional fields in struct iommu_domain to track which devices the mm
was bound to. It doesn't simplify the code much. Any thoughts?

Best regards,
baolu