Re: [PATCH V2] video/aperture: match the pci device when calling sysfb_disable()

[Javier Martinez Canillas <javierm@redhat.com>]

Alex Deucher <alexander.deucher@amd.com> writes:

Hello Alex,

> In aperture_remove_conflicting_pci_devices(), we currently only
> call sysfb_disable() on vga class devices.  This leads to the
> following problem when the pimary device is not VGA compatible:
>
> 1. A PCI device with a non-VGA class is the boot display
> 2. That device is probed first and it is not a VGA device so
>    sysfb_disable() is not called, but the device resources
>    are freed by aperture_detach_platform_device()
> 3. Non-primary GPU has a VGA class and it ends up calling sysfb_disable()
> 4. NULL pointer dereference via sysfb_disable() since the resources
>    have already been freed by aperture_detach_platform_device() when
>    it was called by the other device.
>
> Fix this by passing a device pointer to sysfb_disable() and checking
> the device to determine if we should execute it or not.
>
> v2: Fix build when CONFIG_SCREEN_INFO is not set
>
> Fixes: 5ae3716cfdcd ("video/aperture: Only remove sysfb on the default vga pci device")
> Cc: Javier Martinez Canillas <javierm@redhat.com>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Helge Deller <deller@gmx.de>
> Cc: Sam Ravnborg <sam@ravnborg.org>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
> Cc: stable@vger.kernel.org
> ---

The patch looks good to me.

Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>

I just have to minor comments below:

...

>  /**
>   * sysfb_disable() - disable the Generic System Framebuffers support
> + * @dev:	the device to check if non-NULL
>   *
>   * This disables the registration of system framebuffer devices that match the
>   * generic drivers that make use of the system framebuffer set up by firmware.
> @@ -61,8 +64,12 @@ static bool sysfb_unregister(void)
>   * Context: The function can sleep. A @disable_lock mutex is acquired to serialize
>   *          against sysfb_init(), that registers a system framebuffer device.
>   */
> -void sysfb_disable(void)
> +void sysfb_disable(struct device *dev)
>  {
> +	struct screen_info *si = &screen_info;
> +
> +	if (dev && dev != sysfb_parent_dev(si))
> +		return;

Does this need to be protected by the disable_lock mutex? i.e:

        mutex_lock(&disable_lock);
        if (!dev || dev == sysfb_parent_dev(si) {
                sysfb_unregister();
                disabled = true;
        }
        mutex_unlock(&disable_lock);

...

> @@ -353,8 +353,7 @@ int aperture_remove_conflicting_pci_devices(struct pci_dev *pdev, const char *na
>  	if (pdev == vga_default_device())
>  		primary = true;
>
> -	if (primary)
> -		sysfb_disable();
> +	sysfb_disable(&pdev->dev);
>

After this change the primary variable is only used to determine whether 
__aperture_remove_legacy_vga_devices(pdev) should be called or not. So I
wonder if could just be dropped and instead have:

	/*
	 * If this is the primary adapter, there could be a VGA device
	 * that consumes the VGA framebuffer I/O range. Remove this
	 * device as well.
	 */
	if (pdev == vga_default_device())
		ret = __aperture_remove_legacy_vga_devices(pdev);



-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat