linux-kernel - Re: [PATCH 06/21] vfio/pci: Retrieve preserved device files after Live Update

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Message-ID: <aTAzMUa7Gcm+7j9D@devgpu015.cco6.facebook.com>
Date: Wed, 3 Dec 2025 04:55:13 -0800
From: Alex Mastro <amastro@...com>
To: David Matlack <dmatlack@...gle.com>
CC: Alex Williamson <alex@...zbot.org>,
        Adithya Jayachandran
	<ajayachandra@...dia.com>,
        Alistair Popple <apopple@...dia.com>,
        Andrew
 Morton <akpm@...ux-foundation.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, Chris Li <chrisl@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Jacob Pan
	<jacob.pan@...ux.microsoft.com>,
        Jason Gunthorpe <jgg@...dia.com>, Jason
 Gunthorpe <jgg@...pe.ca>,
        Josh Hilke <jrhilke@...gle.com>, Kevin Tian
	<kevin.tian@...el.com>,
        <kvm@...r.kernel.org>, Leon Romanovsky
	<leonro@...dia.com>,
        <linux-kernel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>,
        <linux-pci@...r.kernel.org>, Lukas Wunner
	<lukas@...ner.de>,
        Mike Rapoport <rppt@...nel.org>, Parav Pandit
	<parav@...dia.com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Philipp
 Stanner <pstanner@...hat.com>,
        Pratyush Yadav <pratyush@...nel.org>,
        Saeed
 Mahameed <saeedm@...dia.com>,
        Samiullah Khawaja <skhawaja@...gle.com>,
        Shuah
 Khan <shuah@...nel.org>, Tomita Moeko <tomitamoeko@...il.com>,
        Vipin Sharma
	<vipinsh@...gle.com>, William Tu <witu@...dia.com>,
        Yi Liu
	<yi.l.liu@...el.com>, Yunxiang Li <Yunxiang.Li@....com>,
        Zhu Yanjun
	<yanjun.zhu@...ux.dev>
Subject: Re: [PATCH 06/21] vfio/pci: Retrieve preserved device files after
 Live Update

On Wed, Nov 26, 2025 at 07:35:53PM +0000, David Matlack wrote:
> From: Vipin Sharma <vipinsh@...gle.com>
>  static int vfio_pci_liveupdate_retrieve(struct liveupdate_file_op_args *args)
>  {
> -	return -EOPNOTSUPP;
> +	struct vfio_pci_core_device_ser *ser;
> +	struct vfio_device *device;
> +	struct folio *folio;
> +	struct file *file;
> +	int ret;
> +
> +	folio = kho_restore_folio(args->serialized_data);
> +	if (!folio)
> +		return -ENOENT;

Should this be consistent with the behavior of pci_flb_retrieve() which panics
on failure? The short circuit failure paths which follow leak the folio,
which seems like a hygiene issue, but the practical significance is moot if
vfio_pci_liveupdate_retrieve() failure is catastrophic anyways?

> +
> +	ser = folio_address(folio);
> +
> +	device = vfio_find_device(ser, match_device);
> +	if (!device)
> +		return -ENODEV;
> +
> +	/*
> +	 * During a Live Update userspace retrieves preserved VFIO cdev files by
> +	 * issuing an ioctl on /dev/liveupdate rather than by opening VFIO
> +	 * character devices.
> +	 *
> +	 * To handle that scenario, this routine simulates opening the VFIO
> +	 * character device for userspace with an anonymous inode. The returned
> +	 * file has the same properties as a cdev file (e.g. operations are
> +	 * blocked until BIND_IOMMUFD is called), aside from the inode
> +	 * association.
> +	 */
> +	file = anon_inode_getfile_fmode("[vfio-device-liveupdate]",
> +					&vfio_device_fops, NULL,
> +					O_RDWR, FMODE_PREAD | FMODE_PWRITE);
> +
> +	if (IS_ERR(file)) {
> +		ret = PTR_ERR(file);
> +		goto out;
> +	}
> +
> +	ret = __vfio_device_fops_cdev_open(device, file);
> +	if (ret) {
> +		fput(file);
> +		goto out;
> +	}
> +
> +	args->file = file;
> +
> +out:
> +	/* Drop the reference from vfio_find_device() */
> +	put_device(&device->device);
> +
> +	return ret;
> +}