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

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Message-ID: <f856519f-419c-1901-b8bc-3e338873157f@amd.com>
Date: Wed, 7 Feb 2024 23:29:46 +0530
From: Vasant Hegde <vasant.hegde@....com>
To: Baolu Lu <baolu.lu@...ux.intel.com>, "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: "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()

Hi Baolu,

On 2/7/2024 5:59 PM, Baolu Lu wrote:
> 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().

Can you please leave a line -OR- move this to previous para? Otherwise we will
get confused.

-Vasant