linux-kernel - Re: [PATCH 26/26] vfio/xe: Add vendor-specific vfio

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Message-ID: <aPgwJ8DHhqCfAdpk@lstrano-desk.jf.intel.com>
Date: Tue, 21 Oct 2025 18:15:19 -0700
From: Matthew Brost <matthew.brost@...el.com>
To: Jason Gunthorpe <jgg@...pe.ca>
CC: Michał Winiarski <michal.winiarski@...el.com>, "Alex
 Williamson" <alex.williamson@...hat.com>, Lucas De Marchi
	<lucas.demarchi@...el.com>, Thomas Hellström
	<thomas.hellstrom@...ux.intel.com>, Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Yishai Hadas <yishaih@...dia.com>, Kevin Tian <kevin.tian@...el.com>,
	"Shameer Kolothum" <shameerali.kolothum.thodi@...wei.com>,
	<intel-xe@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
	<kvm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>, Michal Wajdeczko
	<michal.wajdeczko@...el.com>, Jani Nikula <jani.nikula@...ux.intel.com>,
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>, Tvrtko Ursulin
	<tursulin@...ulin.net>, David Airlie <airlied@...il.com>, Simona Vetter
	<simona@...ll.ch>, Lukasz Laguna <lukasz.laguna@...el.com>
Subject: Re: [PATCH 26/26] vfio/xe: Add vendor-specific vfio_pci driver for
 Intel graphics

On Tue, Oct 21, 2025 at 08:38:11PM -0300, Jason Gunthorpe wrote:
> On Tue, Oct 21, 2025 at 04:14:30PM -0700, Matthew Brost wrote:
> > On Tue, Oct 21, 2025 at 08:03:28PM -0300, Jason Gunthorpe wrote:
> > > On Sat, Oct 11, 2025 at 09:38:47PM +0200, Michał Winiarski wrote:
> > > > +	/*
> > > > +	 * "STOP" handling is reused for "RUNNING_P2P", as the device doesn't have the capability to
> > > > +	 * selectively block p2p DMA transfers.
> > > > +	 * The device is not processing new workload requests when the VF is stopped, and both
> > > > +	 * memory and MMIO communication channels are transferred to destination (where processing
> > > > +	 * will be resumed).
> > > > +	 */
> > > > +	if ((cur == VFIO_DEVICE_STATE_RUNNING && new == VFIO_DEVICE_STATE_STOP) ||
> > > > +	    (cur == VFIO_DEVICE_STATE_RUNNING && new == VFIO_DEVICE_STATE_RUNNING_P2P)) {
> > > > +		ret = xe_sriov_vfio_stop(xe_vdev->pf, xe_vdev->vfid);
> > > 
> > > This comment is not right, RUNNING_P2P means the device can still
> > > receive P2P activity on it's BAR. Eg a GPU will still allow read/write
> > > to its framebuffer.
> > > 
> > > But it is not initiating any new transactions.
> > > 
> > > > +static void xe_vfio_pci_migration_init(struct vfio_device *core_vdev)
> > > > +{
> > > > +	struct xe_vfio_pci_core_device *xe_vdev =
> > > > +		container_of(core_vdev, struct xe_vfio_pci_core_device, core_device.vdev);
> > > > +	struct pci_dev *pdev = to_pci_dev(core_vdev->dev);
> > > > +
> > > > +	if (!xe_sriov_vfio_migration_supported(pdev->physfn))
> > > > +		return;
> > > > +
> > > > +	/* vfid starts from 1 for xe */
> > > > +	xe_vdev->vfid = pci_iov_vf_id(pdev) + 1;
> > > > +	xe_vdev->pf = pdev->physfn;
> > > 
> > > No, this has to use pci_iov_get_pf_drvdata, and this driver should
> > > never have a naked pf pointer flowing around.
> > > 
> > > The entire exported interface is wrongly formed:
> > > 
> > > +bool xe_sriov_vfio_migration_supported(struct pci_dev *pdev);
> > > +int xe_sriov_vfio_wait_flr_done(struct pci_dev *pdev, unsigned int vfid);
> > > +int xe_sriov_vfio_stop(struct pci_dev *pdev, unsigned int vfid);
> > > +int xe_sriov_vfio_run(struct pci_dev *pdev, unsigned int vfid);
> > > +int xe_sriov_vfio_stop_copy_enter(struct pci_dev *pdev, unsigned int vfid);
> > > 
> > > None of these should be taking in a naked pci_dev, it should all work
> > > on whatever type the drvdata is.
> > 
> > This seems entirely backwards. Why would the Xe module export its driver
> > structure to the VFIO module? 
> 
> Because that is how we designed this to work. You've completely
> ignored the safety protocols built into this method.
> 
> > That opens up potential vectors for abuse—for example, the VFIO
> > module accessing internal Xe device structures.
> 
> It does not, just use an opaque struct type.
> 
> > much cleaner to keep interfaces between modules as opaque / generic
> > as possible.
> 
> Nope, don't do that. They should be limited and locked down. Passing
> random pci_devs into these API is going to be bad.


Ok, I think I see what you're getting at. The idea is to call
dev_set_drvdata on the Xe side, then use pci_iov_get_pf_drvdata on the
VFIO side to retrieve that data. This allows passing whatever Xe sets
via dev_set_drvdata between the module interfaces, while only
forward-declaring the interface struct in the shared header.

Am I understanding this correctly?

Matt

> 
> Jason