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

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Message-ID: <BN9PR11MB52766E912B0FD784C5937D078C462@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Tue, 6 Feb 2024 08:09:20 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Baolu Lu <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: 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.