linux-kernel - Re: [PATCH v3 1/4] iommu/vt-d: Implement domain ops for attach_dev

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Message-ID: <00a972f4-1fe2-2eb0-fcf5-d454f3b9dcc6@linux.intel.com>
Date:   Thu, 12 May 2022 09:16:17 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>, dmaengine@...r.kernel.org,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        vkoul@...nel.org, robin.murphy@....com, will@...nel.org,
        Yi Liu <yi.l.liu@...el.com>, Dave Jiang <dave.jiang@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Eric Auger <eric.auger@...hat.com>
Subject: Re: [PATCH v3 1/4] iommu/vt-d: Implement domain ops for
 attach_dev_pasid

On 2022/5/12 01:25, Jacob Pan wrote:
> Hi Jason,
> 
> On Wed, 11 May 2022 14:00:25 -0300, Jason Gunthorpe <jgg@...dia.com> wrote:
> 
>> On Wed, May 11, 2022 at 10:02:16AM -0700, Jacob Pan wrote:
>>>>> If not global, perhaps we could have a list of pasids (e.g. xarray)
>>>>> attached to the device_domain_info. The TLB flush logic would just
>>>>> go through the list w/o caring what the PASIDs are for. Does it
>>>>> make sense to you?
>>>>
>>>> Sort of, but we shouldn't duplicate xarrays - the group already has
>>>> this xarray - need to find some way to allow access to it from the
>>>> driver.
>>>>    
>>> I am not following,  here are the PASIDs for devTLB flush which is per
>>> device. Why group?
>>
>> Because group is where the core code stores it.
> I see, with singleton group. I guess I can let dma-iommu code call
> 
> iommu_attach_dma_pasid {
> 	iommu_attach_device_pasid();
> Then the PASID will be stored in the group xa.
> The flush code can retrieve PASIDs from device_domain_info.device -> group
> -> pasid_array.
> Thanks for pointing it out, I missed the new pasid_array.
>>
>>> We could retrieve PASIDs from the device PASID table but xa would be
>>> more efficient.
>>>    
>>>>>>> Are you suggesting the dma-iommu API should be called
>>>>>>> iommu_set_dma_pasid instead of iommu_attach_dma_pasid?
>>>>>>
>>>>>> No that API is Ok - the driver ops API should be 'set' not
>>>>>> attach/detach
>>>>> Sounds good, this operation has little in common with
>>>>> domain_ops.dev_attach_pasid() used by SVA domain. So I will add a
>>>>> new domain_ops.dev_set_pasid()
>>>>
>>>> What? No, their should only be one operation, 'dev_set_pasid' and it
>>>> is exactly the same as the SVA operation. It configures things so that
>>>> any existing translation on the PASID is removed and the PASID
>>>> translates according to the given domain.
>>>>
>>>> SVA given domain or UNMANAGED given domain doesn't matter to the
>>>> higher level code. The driver should implement per-domain ops as
>>>> required to get the different behaviors.
>>> Perhaps some code to clarify, we have
>>> sva_domain_ops.dev_attach_pasid() = intel_svm_attach_dev_pasid;
>>> default_domain_ops.dev_attach_pasid() = intel_iommu_attach_dev_pasid;
>>
>> Yes, keep that structure
>>   
>>> Consolidate pasid programming into dev_set_pasid() then called by both
>>> intel_svm_attach_dev_pasid() and intel_iommu_attach_dev_pasid(), right?
>>>   
>>
>> I was only suggesting that really dev_attach_pasid() op is misnamed,
>> it should be called set_dev_pasid() and act like a set, not a paired
>> attach/detach - same as the non-PASID ops.
>>
> Got it. Perhaps another patch to rename, Baolu?

Yes. I can rename it in my sva series if others are also happy with this
naming.

Best regards,
baolu