linux-kernel - Re: [PATCH v6 08/12] iommu/sva: Use attach/detach_pasid

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Message-ID: <1a78418a-8637-e8dd-d1de-5529f20058fd@linux.intel.com>
Date:   Thu, 12 May 2022 19:59:41 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, "Tian, Kevin" <kevin.tian@...el.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>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 08/12] iommu/sva: Use attach/detach_pasid_dev in SVA
 interfaces

On 2022/5/12 19:48, Jason Gunthorpe wrote:
> On Thu, May 12, 2022 at 01:17:08PM +0800, Baolu Lu wrote:
>> On 2022/5/12 13:01, Tian, Kevin wrote:
>>>> From: Baolu Lu <baolu.lu@...ux.intel.com>
>>>> Sent: Thursday, May 12, 2022 11:03 AM
>>>>
>>>> On 2022/5/11 22:53, Jason Gunthorpe wrote:
>>>>>>> Also, given the current arrangement it might make sense to have a
>>>>>>> struct iommu_domain_sva given that no driver is wrappering this in
>>>>>>> something else.
>>>>>> Fair enough. How about below wrapper?
>>>>>>
>>>>>> +struct iommu_sva_domain {
>>>>>> +       /*
>>>>>> +        * Common iommu domain header,*must*  be put at the top
>>>>>> +        * of the structure.
>>>>>> +        */
>>>>>> +       struct iommu_domain domain;
>>>>>> +       struct mm_struct *mm;
>>>>>> +       struct iommu_sva bond;
>>>>>> +}
>>>>>>
>>>>>> The refcount is wrapped in bond.
>>>>> I'm still not sure that bond is necessary
>>>>
>>>> "bond" is the sva handle that the device drivers get through calling
>>>> iommu_sva_bind().
>>>>
>>>
>>> 'bond' was required before because we didn't have a domain to wrap
>>> the page table at that time.
>>>
>>> Now we have a domain and it is 1:1 associated to bond. Probably
>>> make sense now by just returning the domain as the sva handle
>>> instead?
>>
>> It also includes the device information that the domain has been
>> attached. So the sva_unbind() looks like this:
>>
>> /**
>>   * iommu_sva_unbind_device() - Remove a bond created with
>> iommu_sva_bind_device
>>   * @handle: the handle returned by iommu_sva_bind_device()
>>   *
>>   * Put reference to a bond between device and address space. The device
>> should
>>   * not be issuing any more transaction for this PASID. All outstanding page
>>   * requests for this PASID must have been flushed to the IOMMU.
>>   */
>> void iommu_sva_unbind_device(struct iommu_sva *handle)
>>
>> It's fine to replace the iommu_sva with iommu_sva_domain for sva handle,
>> if we can include the device in the unbind() interface.
> 
> Why would we have a special unbind for SVA?

It's about SVA kAPI for device drivers. The existing kAPIs include:

struct iommu_sva *iommu_sva_bind_device(struct device *dev,
                                         struct mm_struct *mm,
                                         void *drvdata);
void iommu_sva_unbind_device(struct iommu_sva *handle);
u32 iommu_sva_get_pasid(struct iommu_sva *handle);

> SVA should not different from normal domains it should use the normal
> detach flow too.

Best regards,
baolu