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

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Message-ID: <BN9PR11MB5276E70CAB272B212977F0C98C472@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Mon, 5 Feb 2024 09:00:51 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Lu Baolu <baolu.lu@...ux.intel.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 v11 13/16] iommu: Improve iopf_queue_remove_device()

> 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.

> + * - 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.