linux-kernel - Re: [PATCH v4 7/8] PCI/VGA: Move check for firmware default out of VGA arbiter

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <f0e70269-b55e-4ac8-b052-da092a177eda@suse.de>
Date: Tue, 24 Jun 2025 11:21:23 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Mario Limonciello <superm1@...nel.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>
Cc: Alex Deucher <alexander.deucher@....com>,
 Christian König <christian.koenig@....com>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Lukas Wunner <lukas@...ner.de>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, David Woodhouse <dwmw2@...radead.org>,
 Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Alex Williamson <alex.williamson@...hat.com>,
 Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
 "open list:DRM DRIVERS" <dri-devel@...ts.freedesktop.org>,
 open list <linux-kernel@...r.kernel.org>,
 "open list:INTEL IOMMU (VT-d)" <iommu@...ts.linux.dev>,
 "open list:PCI SUBSYSTEM" <linux-pci@...r.kernel.org>,
 "open list:VFIO DRIVER" <kvm@...r.kernel.org>,
 "open list:SOUND" <linux-sound@...r.kernel.org>,
 Daniel Dadap <ddadap@...dia.com>,
 Mario Limonciello <mario.limonciello@....com>
Subject: Re: [PATCH v4 7/8] PCI/VGA: Move check for firmware default out of
 VGA arbiter



Am 23.06.25 um 20:47 schrieb Mario Limonciello:
> From: Mario Limonciello <mario.limonciello@....com>
>
> The x86 specific check for whether a framebuffer belongs to a device
> works for display devices as well as VGA devices.  Callers to
> video_is_primary_device() can benefit from checking non-VGA display
> devices.
>
> Move the x86 specific check into x86 specific code, and adjust VGA
> arbiter to call that code as well. This allows fbcon to find the
> right PCI device on systems that don't have VGA devices.
>
> Suggested-by: Thomas Zimmermann <tzimmermann@...e.de>
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
> v4:
>   * use helper
> ---
>   arch/x86/video/video-common.c | 13 ++++++++++++-
>   drivers/pci/vgaarb.c          | 36 ++---------------------------------
>   2 files changed, 14 insertions(+), 35 deletions(-)
>
> diff --git a/arch/x86/video/video-common.c b/arch/x86/video/video-common.c
> index 81fc97a2a837a..917568e4d7fb1 100644
> --- a/arch/x86/video/video-common.c
> +++ b/arch/x86/video/video-common.c
> @@ -9,6 +9,7 @@
>   
>   #include <linux/module.h>
>   #include <linux/pci.h>
> +#include <linux/screen_info.h>
>   #include <linux/vgaarb.h>
>   
>   #include <asm/video.h>
> @@ -27,6 +28,7 @@ EXPORT_SYMBOL(pgprot_framebuffer);
>   
>   bool video_is_primary_device(struct device *dev)
>   {
> +	struct screen_info *si = &screen_info;
>   	struct pci_dev *pdev;
>   
>   	if (!dev_is_pci(dev))
> @@ -34,7 +36,16 @@ bool video_is_primary_device(struct device *dev)
>   
>   	pdev = to_pci_dev(dev);
>   
> -	return (pdev == vga_default_device());
> +	if (!pci_is_display(pdev))
> +		return false;
> +
> +	if (pdev == vga_default_device())
> +		return true;
> +
> +	if (pdev == screen_info_pci_dev(si))
> +		return true;
> +
> +	return false;
>   }
>   EXPORT_SYMBOL(video_is_primary_device);
>   
> diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
> index 78748e8d2dbae..15ab58c70b016 100644
> --- a/drivers/pci/vgaarb.c
> +++ b/drivers/pci/vgaarb.c
> @@ -26,12 +26,12 @@
>   #include <linux/poll.h>
>   #include <linux/miscdevice.h>
>   #include <linux/slab.h>
> -#include <linux/screen_info.h>
>   #include <linux/vt.h>
>   #include <linux/console.h>
>   #include <linux/acpi.h>
>   #include <linux/uaccess.h>
>   #include <linux/vgaarb.h>
> +#include <asm/video.h>
>   
>   static void vga_arbiter_notify_clients(void);
>   
> @@ -554,38 +554,6 @@ void vga_put(struct pci_dev *pdev, unsigned int rsrc)
>   }
>   EXPORT_SYMBOL(vga_put);
>   
> -static bool vga_is_firmware_default(struct pci_dev *pdev)
> -{
> -#if defined(CONFIG_X86)
> -	u64 base = screen_info.lfb_base;
> -	u64 size = screen_info.lfb_size;
> -	struct resource *r;
> -	u64 limit;
> -
> -	/* Select the device owning the boot framebuffer if there is one */
> -
> -	if (screen_info.capabilities & VIDEO_CAPABILITY_64BIT_BASE)
> -		base |= (u64)screen_info.ext_lfb_base << 32;
> -
> -	limit = base + size;
> -
> -	/* Does firmware framebuffer belong to us? */
> -	pci_dev_for_each_resource(pdev, r) {
> -		if (resource_type(r) != IORESOURCE_MEM)
> -			continue;
> -
> -		if (!r->start || !r->end)
> -			continue;
> -
> -		if (base < r->start || limit >= r->end)
> -			continue;
> -
> -		return true;
> -	}
> -#endif
> -	return false;
> -}
> -
>   static bool vga_arb_integrated_gpu(struct device *dev)
>   {
>   #if defined(CONFIG_ACPI)
> @@ -623,7 +591,7 @@ static bool vga_is_boot_device(struct vga_device *vgadev)
>   	if (boot_vga && boot_vga->is_firmware_default)
>   		return false;
>   
> -	if (vga_is_firmware_default(pdev)) {
> +	if (video_is_primary_device(&pdev->dev)) {

Doesn't this generate a cyclic dependency between vgaarb and video? I 
find this call cycle hard to reason about because 
vgaarb_default_device() depends on the results of these boot-device 
tests. Maybe keep vga_is_firmware_default() and just replace its content 
with a call to screen_info_pci_dev().
Best regards
Thomas

>   		vgadev->is_firmware_default = true;
>   		return true;
>   	}

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)