linux-kernel - Re: [PATCH] vfio/pci: update igd matching conditions

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Message-ID: <20241229092600.00ffa55f.alex.williamson@redhat.com>
Date: Sun, 29 Dec 2024 09:26:00 -0700
From: Alex Williamson <alex.williamson@...hat.com>
To: Tomita Moeko <tomitamoeko@...il.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfio/pci: update igd matching conditions

On Sun, 29 Dec 2024 23:51:40 +0800
Tomita Moeko <tomitamoeko@...il.com> wrote:

> igd device can either expose as a VGA controller or display controller
> depending on whether it is configured as the primary display device in
> BIOS. In both cases, the OpRegion may be present. Also checks if the
> device is at bdf 00:02.0 to avoid setting up igd-specific regions on
> Intel discrete GPUs.
> 
> Signed-off-by: Tomita Moeko <tomitamoeko@...il.com>
> ---
>  drivers/vfio/pci/vfio_pci.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index e727941f589d..051ef4ad3f43 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -111,9 +111,11 @@ static int vfio_pci_open_device(struct vfio_device *core_vdev)
>  	if (ret)
>  		return ret;
>  
> -	if (vfio_pci_is_vga(pdev) &&
> +	if (IS_ENABLED(CONFIG_VFIO_PCI_IGD) &&
>  	    pdev->vendor == PCI_VENDOR_ID_INTEL &&
> -	    IS_ENABLED(CONFIG_VFIO_PCI_IGD)) {
> +	    ((pdev->class >> 8) == PCI_CLASS_DISPLAY_VGA ||

The above is vfio_pci_is_vga(pdev), maybe below should have a similar
helper.

> +	     (pdev->class >> 8) == PCI_CLASS_DISPLAY_OTHER) &&
> +	    pdev == pci_get_domain_bus_and_slot(0, 0, PCI_DEVFN(2, 0))) {

This increments the reference count on the device:

 * Given a PCI domain, bus, and slot/function number, the desired PCI
 * device is located in the list of PCI devices. If the device is
 * found, its reference count is increased and this function returns a
 * pointer to its data structure.  The caller must decrement the
 * reference count by calling pci_dev_put().

>  		ret = vfio_pci_igd_init(vdev);
>  		if (ret && ret != -ENODEV) {
>  			pci_warn(pdev, "Failed to setup Intel IGD regions\n");