linux-kernel - Re: [PATCH v11 13/16] iommu: Improve iopf_queue_remove

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Date: Tue, 6 Feb 2024 16:33:14 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: "Tian, Kevin" <kevin.tian@...el.com>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Jason Gunthorpe <jgg@...pe.ca>,
 Jean-Philippe Brucker <jean-philippe@...aro.org>,
 Nicolin Chen <nicolinc@...dia.com>
Cc: baolu.lu@...ux.intel.com, "Liu, Yi L" <yi.l.liu@...el.com>,
 Jacob Pan <jacob.jun.pan@...ux.intel.com>,
 Longfang Liu <liulongfang@...wei.com>, "Zhao, Yan Y" <yan.y.zhao@...el.com>,
 Joel Granados <j.granados@...sung.com>,
 "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
 "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH v11 13/16] iommu: Improve iopf_queue_remove_device()

On 2024/2/6 16:09, Tian, Kevin wrote:
>> From: Baolu Lu <baolu.lu@...ux.intel.com>
>> Sent: Monday, February 5, 2024 7:55 PM
>>
>> On 2024/2/5 17:00, Tian, Kevin wrote:
>>>> From: Lu Baolu <baolu.lu@...ux.intel.com>
>>>> Sent: Tuesday, January 30, 2024 4:09 PM
>>>>     *
>>>> - * Caller makes sure that no more faults are reported for this device.
>>>> + * Removing a device from an iopf_queue. It's recommended to follow
>>>> these
>>>> + * steps when removing a device:
>>>>     *
>>>> - * Return: 0 on success and <0 on error.
>>>> + * - Disable new PRI reception: Turn off PRI generation in the IOMMU
>>>> hardware
>>>> + *   and flush any hardware page request queues. This should be done
>>>> before
>>>> + *   calling into this helper.
>>>
>>> this 1st step is already not followed by intel-iommu driver. The Page
>>> Request Enable (PRE) bit is set in the context entry when a device
>>> is attached to the default domain and cleared only in
>>> intel_iommu_release_device().
>>>
>>> but iopf_queue_remove_device() is called when IOMMU_DEV_FEAT_IOPF
>>> is disabled e.g. when idxd driver is unbound from the device.
>>>
>>> so the order is already violated.
>>>
>>>> + * - Acknowledge all outstanding PRQs to the device: Respond to all
>>>> outstanding
>>>> + *   page requests with IOMMU_PAGE_RESP_INVALID, indicating the
>> device
>>>> should
>>>> + *   not retry. This helper function handles this.
>>>> + * - Disable PRI on the device: After calling this helper, the caller could
>>>> + *   then disable PRI on the device.
>>>
>>> intel_iommu_disable_iopf() disables PRI cap before calling this helper.
>>
>> You are right. The individual drivers should be adjusted accordingly in
>> separated patches. Here we just define the expected behaviors of the
>> individual iommu driver from the core's perspective.
> 
> can you add a note in commit msg about it?
> 
>>
>>>
>>>> + * - Tear down the iopf infrastructure: Calling
>> iopf_queue_remove_device()
>>>> + *   essentially disassociates the device. The fault_param might still exist,
>>>> + *   but iommu_page_response() will do nothing. The device fault
>> parameter
>>>> + *   reference count has been properly passed from
>>>> iommu_report_device_fault()
>>>> + *   to the fault handling work, and will eventually be released after
>>>> + *   iommu_page_response().
>>>
>>> it's unclear what 'tear down' means here.
>>
>> It's the same as calling iopf_queue_remove_device(). Perhaps I could
>> remove the confusing "tear down the iopf infrastructure"?
>>
> 
> I thought it is the last step then must have something real to do.
> 
> if not then removing it is clearer.

Both done. Thanks!

Best regards,
baolu