* Re: [PATCH 6.12 126/132] drm, fbcon, vga_switcheroo: Avoid race condition in fbcon setup
2025-12-03 15:30 ` [PATCH 6.12 126/132] drm, fbcon, vga_switcheroo: Avoid race condition in fbcon setup Greg Kroah-Hartman
@ 2025-12-03 17:15 ` Thomas Zimmermann
0 siblings, 0 replies; 2+ messages in thread
From: Thomas Zimmermann @ 2025-12-03 17:15 UTC (permalink / raw)
To: Greg Kroah-Hartman, stable
Cc: patches, Javier Martinez Canillas, Alex Deucher, dri-devel,
nouveau, amd-gfx, linux-fbdev, Sasha Levin
Hi,
thank you for making the updated patch.
Am 03.12.25 um 16:30 schrieb Greg Kroah-Hartman:
> 6.12-stable review patch. If anyone has any objections, please let me know.
>
> ------------------
>
> From: Thomas Zimmermann <tzimmermann@suse.de>
>
> [ Upstream commit eb76d0f5553575599561010f24c277cc5b31d003 ]
>
> Protect vga_switcheroo_client_fb_set() with console lock. Avoids OOB
> access in fbcon_remap_all(). Without holding the console lock the call
> races with switching outputs.
>
> VGA switcheroo calls fbcon_remap_all() when switching clients. The fbcon
> function uses struct fb_info.node, which is set by register_framebuffer().
> As the fb-helper code currently sets up VGA switcheroo before registering
> the framebuffer, the value of node is -1 and therefore not a legal value.
> For example, fbcon uses the value within set_con2fb_map() [1] as an index
> into an array.
>
> Moving vga_switcheroo_client_fb_set() after register_framebuffer() can
> result in VGA switching that does not switch fbcon correctly.
>
> Therefore move vga_switcheroo_client_fb_set() under fbcon_fb_registered(),
> which already holds the console lock. Fbdev calls fbcon_fb_registered()
> from within register_framebuffer(). Serializes the helper with VGA
> switcheroo's call to fbcon_remap_all().
>
> Although vga_switcheroo_client_fb_set() takes an instance of struct fb_info
> as parameter, it really only needs the contained fbcon state. Moving the
> call to fbcon initialization is therefore cleaner than before. Only amdgpu,
> i915, nouveau and radeon support vga_switcheroo. For all other drivers,
> this change does nothing.
>
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> Link: https://elixir.bootlin.com/linux/v6.17/source/drivers/video/fbdev/core/fbcon.c#L2942 # [1]
> Fixes: 6a9ee8af344e ("vga_switcheroo: initial implementation (v15)")
> Acked-by: Javier Martinez Canillas <javierm@redhat.com>
> Acked-by: Alex Deucher <alexander.deucher@amd.com>
> Cc: dri-devel@lists.freedesktop.org
> Cc: nouveau@lists.freedesktop.org
> Cc: amd-gfx@lists.freedesktop.org
> Cc: linux-fbdev@vger.kernel.org
> Cc: <stable@vger.kernel.org> # v2.6.34+
> Link: https://patch.msgid.link/20251105161549.98836-1-tzimmermann@suse.de
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
> ---
> drivers/gpu/drm/drm_fb_helper.c | 6 ------
> drivers/gpu/drm/i915/display/intel_fbdev.c | 6 ------
> drivers/gpu/drm/radeon/radeon_fbdev.c | 5 -----
> drivers/video/fbdev/core/fbcon.c | 9 +++++++++
> 4 files changed, 9 insertions(+), 17 deletions(-)
>
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -30,9 +30,7 @@
> #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>
> #include <linux/console.h>
> -#include <linux/pci.h>
> #include <linux/sysrq.h>
> -#include <linux/vga_switcheroo.h>
>
> #include <drm/drm_atomic.h>
> #include <drm/drm_drv.h>
> @@ -1637,10 +1635,6 @@ static int drm_fb_helper_single_fb_probe
>
> strcpy(fb_helper->fb->comm, "[fbcon]");
>
> - /* Set the fb info for vgaswitcheroo clients. Does nothing otherwise. */
> - if (dev_is_pci(dev->dev))
> - vga_switcheroo_client_fb_set(to_pci_dev(dev->dev), fb_helper->info);
> -
> return 0;
> }
>
> --- a/drivers/gpu/drm/i915/display/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/display/intel_fbdev.c
> @@ -589,11 +589,8 @@ static int intel_fbdev_restore_mode(stru
> static void intel_fbdev_client_unregister(struct drm_client_dev *client)
> {
> struct drm_fb_helper *fb_helper = drm_fb_helper_from_client(client);
> - struct drm_device *dev = fb_helper->dev;
> - struct pci_dev *pdev = to_pci_dev(dev->dev);
>
> if (fb_helper->info) {
> - vga_switcheroo_client_fb_set(pdev, NULL);
> drm_fb_helper_unregister_info(fb_helper);
> } else {
> drm_fb_helper_unprepare(fb_helper);
> @@ -620,7 +617,6 @@ static int intel_fbdev_client_hotplug(st
> {
> struct drm_fb_helper *fb_helper = drm_fb_helper_from_client(client);
> struct drm_device *dev = client->dev;
> - struct pci_dev *pdev = to_pci_dev(dev->dev);
> int ret;
>
> if (dev->fb_helper)
> @@ -634,8 +630,6 @@ static int intel_fbdev_client_hotplug(st
> if (ret)
> goto err_drm_fb_helper_fini;
>
> - vga_switcheroo_client_fb_set(pdev, fb_helper->info);
> -
> return 0;
>
> err_drm_fb_helper_fini:
> --- a/drivers/gpu/drm/radeon/radeon_fbdev.c
> +++ b/drivers/gpu/drm/radeon/radeon_fbdev.c
> @@ -300,10 +300,8 @@ static void radeon_fbdev_client_unregist
> {
> struct drm_fb_helper *fb_helper = drm_fb_helper_from_client(client);
> struct drm_device *dev = fb_helper->dev;
> - struct radeon_device *rdev = dev->dev_private;
>
> if (fb_helper->info) {
> - vga_switcheroo_client_fb_set(rdev->pdev, NULL);
> drm_helper_force_disable_all(dev);
> drm_fb_helper_unregister_info(fb_helper);
> } else {
> @@ -325,7 +323,6 @@ static int radeon_fbdev_client_hotplug(s
> {
> struct drm_fb_helper *fb_helper = drm_fb_helper_from_client(client);
> struct drm_device *dev = client->dev;
> - struct radeon_device *rdev = dev->dev_private;
> int ret;
>
> if (dev->fb_helper)
> @@ -342,8 +339,6 @@ static int radeon_fbdev_client_hotplug(s
> if (ret)
> goto err_drm_fb_helper_fini;
>
> - vga_switcheroo_client_fb_set(rdev->pdev, fb_helper->info);
> -
> return 0;
>
> err_drm_fb_helper_fini:
> --- a/drivers/video/fbdev/core/fbcon.c
> +++ b/drivers/video/fbdev/core/fbcon.c
> @@ -65,6 +65,7 @@
> #include <linux/string.h>
> #include <linux/kd.h>
> #include <linux/panic.h>
> +#include <linux/pci.h>
> #include <linux/printk.h>
> #include <linux/slab.h>
> #include <linux/fb.h>
> @@ -77,6 +78,7 @@
> #include <linux/interrupt.h>
> #include <linux/crc32.h> /* For counting font checksums */
> #include <linux/uaccess.h>
> +#include <linux/vga_switcheroo.h>
> #include <asm/irq.h>
>
> #include "fbcon.h"
> @@ -2894,6 +2896,9 @@ void fbcon_fb_unregistered(struct fb_inf
>
> console_lock();
>
> + if (info->device && dev_is_pci(info->device))
> + vga_switcheroo_client_fb_set(to_pci_dev(info->device), NULL);
> +
> fbcon_registered_fb[info->node] = NULL;
> fbcon_num_registered_fb--;
>
> @@ -3027,6 +3032,10 @@ static int do_fb_registered(struct fb_in
> }
> }
>
> + /* Set the fb info for vga_switcheroo clients. Does nothing otherwise. */
> + if (info->device && dev_is_pci(info->device))
> + vga_switcheroo_client_fb_set(to_pci_dev(info->device), info);
> +
> return ret;
> }
>
>
>
>
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)
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