linux-kernel - Re: [PATCH v12 13/16] iommu: Improve iopf_queue_remove

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Date: Wed, 7 Feb 2024 20:29:45 +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 v12 13/16] iommu: Improve iopf_queue_remove_device()

On 2024/2/7 10:50, Tian, Kevin wrote:
>> From: Lu Baolu<baolu.lu@...ux.intel.com>
>> Sent: Wednesday, February 7, 2024 9:33 AM
>>
>> Convert iopf_queue_remove_device() to return void instead of an error code,
>> as the return value is never used. This removal helper is designed to be
>> never-failed, so there's no need for error handling.
>>
>> Ack all outstanding page requests from the device with the response code of
>> IOMMU_PAGE_RESP_INVALID, indicating device should not attempt any retry.
>>
>> Add comments to this helper explaining the steps involved in removing a
>> device from the iopf queue and disabling its PRI. The individual drivers
>> are expected to be adjusted accordingly. Here we just define the expected
>> behaviors of the individual iommu driver from the core's perspective.
>>
>> Suggested-by: Jason Gunthorpe<jgg@...dia.com>
>> Signed-off-by: Lu Baolu<baolu.lu@...ux.intel.com>
>> Reviewed-by: Jason Gunthorpe<jgg@...dia.com>
>> Tested-by: Yan Zhao<yan.y.zhao@...el.com>
> Reviewed-by: Kevin Tian<kevin.tian@...el.com>, with one nit:
> 
>> + * 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.
>> + * - 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.
> this implies calling iopf_queue_remove_device() here.
> 
>> + * - Disable PRI on the device: After calling this helper, the caller could
>> + *   then disable PRI on the device.
>> + * - Call iopf_queue_remove_device(): 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().
>>    */
> but here it suggests calling iopf_queue_remove_device() again. If the comment
> is just about to detail the behavior with that invocation shouldn't it be merged
> with the previous one instead of pretending to be the final step for driver
> to call?

Above just explains the behavior of calling iopf_queue_remove_device().

Best regards,
baolu