* [PATCH 1/2] drm, fbcon, vga_switcheroo: Avoid race condition in fbcon setup
[not found] <20260120081841.9827-1-tzimmermann@suse.com>
@ 2026-01-20 8:13 ` Thomas Zimmermann
2026-01-20 8:20 ` Thomas Zimmermann
0 siblings, 1 reply; 4+ messages in thread
From: Thomas Zimmermann @ 2026-01-20 8:13 UTC (permalink / raw)
To: kernel-kabi
Cc: Thomas Zimmermann, Javier Martinez Canillas, Alex Deucher,
dri-devel, nouveau, amd-gfx, linux-fbdev, stable
From: Thomas Zimmermann <tzimmermann@suse.de>
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
(cherry picked from commit eb76d0f5553575599561010f24c277cc5b31d003)
---
drivers/gpu/drm/drm_fb_helper.c | 6 ------
drivers/gpu/drm/i915/display/intel_fbdev.c | 2 --
drivers/gpu/drm/radeon/radeon_fbdev.c | 3 ---
drivers/video/fbdev/core/fbcon.c | 9 +++++++++
4 files changed, 9 insertions(+), 11 deletions(-)
diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index b507c1c008a3e..3915a8b17bc4c 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -32,7 +32,6 @@
#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>
@@ -1668,7 +1667,6 @@ static int drm_fb_helper_find_sizes(struct drm_fb_helper *fb_helper,
static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper)
{
struct drm_client_dev *client = &fb_helper->client;
- struct drm_device *dev = fb_helper->dev;
struct drm_fb_helper_surface_size sizes;
int ret;
@@ -1687,10 +1685,6 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper)
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;
}
diff --git a/drivers/gpu/drm/i915/display/intel_fbdev.c b/drivers/gpu/drm/i915/display/intel_fbdev.c
index 31d0d695d5671..8bad7e7909f7b 100644
--- a/drivers/gpu/drm/i915/display/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/display/intel_fbdev.c
@@ -36,7 +36,6 @@
#include <linux/string.h>
#include <linux/sysrq.h>
#include <linux/tty.h>
-#include <linux/vga_switcheroo.h>
#include <drm/drm_crtc.h>
#include <drm/drm_fb_helper.h>
@@ -337,7 +336,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
ifbdev->vma_flags = flags;
intel_runtime_pm_put(&dev_priv->runtime_pm, wakeref);
- vga_switcheroo_client_fb_set(pdev, info);
return 0;
out_unpin:
diff --git a/drivers/gpu/drm/radeon/radeon_fbdev.c b/drivers/gpu/drm/radeon/radeon_fbdev.c
index fb70de29545c6..730efabe05f6b 100644
--- a/drivers/gpu/drm/radeon/radeon_fbdev.c
+++ b/drivers/gpu/drm/radeon/radeon_fbdev.c
@@ -303,7 +303,6 @@ static void radeon_fbdev_client_unregister(struct drm_client_dev *client)
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 {
@@ -342,8 +341,6 @@ static int radeon_fbdev_client_hotplug(struct drm_client_dev *client)
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:
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 79525ee90e3b2..57b21b6869231 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -64,6 +64,7 @@
#include <linux/console.h>
#include <linux/string.h>
#include <linux/kd.h>
+#include <linux/pci.h>
#include <linux/slab.h>
#include <linux/fb.h>
#include <linux/fbcon.h>
@@ -75,6 +76,7 @@
#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"
@@ -2909,6 +2911,9 @@ void fbcon_fb_unregistered(struct fb_info *info)
console_lock();
+ if (info->device && dev_is_pci(info->device))
+ vga_switcheroo_client_fb_set(to_pci_dev(info->device), info);
+
fbcon_registered_fb[info->node] = NULL;
fbcon_num_registered_fb--;
@@ -3042,6 +3047,10 @@ static int do_fb_registered(struct fb_info *info)
}
}
+ /* 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), NULL);
+
return ret;
}
--
2.52.0
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH 1/2] drm, fbcon, vga_switcheroo: Avoid race condition in fbcon setup
2026-01-20 8:13 ` [PATCH 1/2] drm, fbcon, vga_switcheroo: Avoid race condition in fbcon setup Thomas Zimmermann
@ 2026-01-20 8:20 ` Thomas Zimmermann
0 siblings, 0 replies; 4+ messages in thread
From: Thomas Zimmermann @ 2026-01-20 8:20 UTC (permalink / raw)
To: Thomas Zimmermann
Cc: Javier Martinez Canillas, Alex Deucher, dri-devel, nouveau,
amd-gfx, linux-fbdev, stable
Please ignore. This patch has been merged already.
Am 20.01.26 um 09:13 schrieb Thomas Zimmermann:
> From: Thomas Zimmermann <tzimmermann@suse.de>
>
> 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
> (cherry picked from commit eb76d0f5553575599561010f24c277cc5b31d003)
> ---
> drivers/gpu/drm/drm_fb_helper.c | 6 ------
> drivers/gpu/drm/i915/display/intel_fbdev.c | 2 --
> drivers/gpu/drm/radeon/radeon_fbdev.c | 3 ---
> drivers/video/fbdev/core/fbcon.c | 9 +++++++++
> 4 files changed, 9 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index b507c1c008a3e..3915a8b17bc4c 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -32,7 +32,6 @@
> #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>
> @@ -1668,7 +1667,6 @@ static int drm_fb_helper_find_sizes(struct drm_fb_helper *fb_helper,
> static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper)
> {
> struct drm_client_dev *client = &fb_helper->client;
> - struct drm_device *dev = fb_helper->dev;
> struct drm_fb_helper_surface_size sizes;
> int ret;
>
> @@ -1687,10 +1685,6 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper)
>
> 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;
> }
>
> diff --git a/drivers/gpu/drm/i915/display/intel_fbdev.c b/drivers/gpu/drm/i915/display/intel_fbdev.c
> index 31d0d695d5671..8bad7e7909f7b 100644
> --- a/drivers/gpu/drm/i915/display/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/display/intel_fbdev.c
> @@ -36,7 +36,6 @@
> #include <linux/string.h>
> #include <linux/sysrq.h>
> #include <linux/tty.h>
> -#include <linux/vga_switcheroo.h>
>
> #include <drm/drm_crtc.h>
> #include <drm/drm_fb_helper.h>
> @@ -337,7 +336,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
> ifbdev->vma_flags = flags;
>
> intel_runtime_pm_put(&dev_priv->runtime_pm, wakeref);
> - vga_switcheroo_client_fb_set(pdev, info);
> return 0;
>
> out_unpin:
> diff --git a/drivers/gpu/drm/radeon/radeon_fbdev.c b/drivers/gpu/drm/radeon/radeon_fbdev.c
> index fb70de29545c6..730efabe05f6b 100644
> --- a/drivers/gpu/drm/radeon/radeon_fbdev.c
> +++ b/drivers/gpu/drm/radeon/radeon_fbdev.c
> @@ -303,7 +303,6 @@ static void radeon_fbdev_client_unregister(struct drm_client_dev *client)
> 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 {
> @@ -342,8 +341,6 @@ static int radeon_fbdev_client_hotplug(struct drm_client_dev *client)
> 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:
> diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> index 79525ee90e3b2..57b21b6869231 100644
> --- a/drivers/video/fbdev/core/fbcon.c
> +++ b/drivers/video/fbdev/core/fbcon.c
> @@ -64,6 +64,7 @@
> #include <linux/console.h>
> #include <linux/string.h>
> #include <linux/kd.h>
> +#include <linux/pci.h>
> #include <linux/slab.h>
> #include <linux/fb.h>
> #include <linux/fbcon.h>
> @@ -75,6 +76,7 @@
> #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"
> @@ -2909,6 +2911,9 @@ void fbcon_fb_unregistered(struct fb_info *info)
>
> console_lock();
>
> + if (info->device && dev_is_pci(info->device))
> + vga_switcheroo_client_fb_set(to_pci_dev(info->device), info);
> +
> fbcon_registered_fb[info->node] = NULL;
> fbcon_num_registered_fb--;
>
> @@ -3042,6 +3047,10 @@ static int do_fb_registered(struct fb_info *info)
> }
> }
>
> + /* 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), NULL);
> +
> 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)
^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH 1/2] drm, fbcon, vga_switcheroo: Avoid race condition in fbcon setup
[not found] <20260120082841.11381-1-tzimmermann@suse.com>
@ 2026-01-20 8:28 ` Thomas Zimmermann
2026-01-20 8:29 ` Thomas Zimmermann
0 siblings, 1 reply; 4+ messages in thread
From: Thomas Zimmermann @ 2026-01-20 8:28 UTC (permalink / raw)
To: kernel-kabi
Cc: Thomas Zimmermann, Javier Martinez Canillas, Alex Deucher,
dri-devel, nouveau, amd-gfx, linux-fbdev, stable
From: Thomas Zimmermann <tzimmermann@suse.de>
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
(cherry picked from commit eb76d0f5553575599561010f24c277cc5b31d003)
---
drivers/gpu/drm/drm_fb_helper.c | 6 ------
drivers/gpu/drm/i915/display/intel_fbdev.c | 2 --
drivers/gpu/drm/radeon/radeon_fbdev.c | 3 ---
drivers/video/fbdev/core/fbcon.c | 9 +++++++++
4 files changed, 9 insertions(+), 11 deletions(-)
diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index b507c1c008a3e..3915a8b17bc4c 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -32,7 +32,6 @@
#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>
@@ -1668,7 +1667,6 @@ static int drm_fb_helper_find_sizes(struct drm_fb_helper *fb_helper,
static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper)
{
struct drm_client_dev *client = &fb_helper->client;
- struct drm_device *dev = fb_helper->dev;
struct drm_fb_helper_surface_size sizes;
int ret;
@@ -1687,10 +1685,6 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper)
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;
}
diff --git a/drivers/gpu/drm/i915/display/intel_fbdev.c b/drivers/gpu/drm/i915/display/intel_fbdev.c
index 31d0d695d5671..8bad7e7909f7b 100644
--- a/drivers/gpu/drm/i915/display/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/display/intel_fbdev.c
@@ -36,7 +36,6 @@
#include <linux/string.h>
#include <linux/sysrq.h>
#include <linux/tty.h>
-#include <linux/vga_switcheroo.h>
#include <drm/drm_crtc.h>
#include <drm/drm_fb_helper.h>
@@ -337,7 +336,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
ifbdev->vma_flags = flags;
intel_runtime_pm_put(&dev_priv->runtime_pm, wakeref);
- vga_switcheroo_client_fb_set(pdev, info);
return 0;
out_unpin:
diff --git a/drivers/gpu/drm/radeon/radeon_fbdev.c b/drivers/gpu/drm/radeon/radeon_fbdev.c
index fb70de29545c6..730efabe05f6b 100644
--- a/drivers/gpu/drm/radeon/radeon_fbdev.c
+++ b/drivers/gpu/drm/radeon/radeon_fbdev.c
@@ -303,7 +303,6 @@ static void radeon_fbdev_client_unregister(struct drm_client_dev *client)
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 {
@@ -342,8 +341,6 @@ static int radeon_fbdev_client_hotplug(struct drm_client_dev *client)
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:
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 79525ee90e3b2..57b21b6869231 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -64,6 +64,7 @@
#include <linux/console.h>
#include <linux/string.h>
#include <linux/kd.h>
+#include <linux/pci.h>
#include <linux/slab.h>
#include <linux/fb.h>
#include <linux/fbcon.h>
@@ -75,6 +76,7 @@
#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"
@@ -2909,6 +2911,9 @@ void fbcon_fb_unregistered(struct fb_info *info)
console_lock();
+ if (info->device && dev_is_pci(info->device))
+ vga_switcheroo_client_fb_set(to_pci_dev(info->device), info);
+
fbcon_registered_fb[info->node] = NULL;
fbcon_num_registered_fb--;
@@ -3042,6 +3047,10 @@ static int do_fb_registered(struct fb_info *info)
}
}
+ /* 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), NULL);
+
return ret;
}
--
2.52.0
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH 1/2] drm, fbcon, vga_switcheroo: Avoid race condition in fbcon setup
2026-01-20 8:28 ` Thomas Zimmermann
@ 2026-01-20 8:29 ` Thomas Zimmermann
0 siblings, 0 replies; 4+ messages in thread
From: Thomas Zimmermann @ 2026-01-20 8:29 UTC (permalink / raw)
To: Thomas Zimmermann
Cc: Javier Martinez Canillas, Alex Deucher, dri-devel, nouveau,
amd-gfx, linux-fbdev, stable
Please ignore. This patch has been merged already.
Am 20.01.26 um 09:28 schrieb Thomas Zimmermann:
> From: Thomas Zimmermann <tzimmermann@suse.de>
>
> 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
> (cherry picked from commit eb76d0f5553575599561010f24c277cc5b31d003)
> ---
> drivers/gpu/drm/drm_fb_helper.c | 6 ------
> drivers/gpu/drm/i915/display/intel_fbdev.c | 2 --
> drivers/gpu/drm/radeon/radeon_fbdev.c | 3 ---
> drivers/video/fbdev/core/fbcon.c | 9 +++++++++
> 4 files changed, 9 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index b507c1c008a3e..3915a8b17bc4c 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -32,7 +32,6 @@
> #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>
> @@ -1668,7 +1667,6 @@ static int drm_fb_helper_find_sizes(struct drm_fb_helper *fb_helper,
> static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper)
> {
> struct drm_client_dev *client = &fb_helper->client;
> - struct drm_device *dev = fb_helper->dev;
> struct drm_fb_helper_surface_size sizes;
> int ret;
>
> @@ -1687,10 +1685,6 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper)
>
> 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;
> }
>
> diff --git a/drivers/gpu/drm/i915/display/intel_fbdev.c b/drivers/gpu/drm/i915/display/intel_fbdev.c
> index 31d0d695d5671..8bad7e7909f7b 100644
> --- a/drivers/gpu/drm/i915/display/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/display/intel_fbdev.c
> @@ -36,7 +36,6 @@
> #include <linux/string.h>
> #include <linux/sysrq.h>
> #include <linux/tty.h>
> -#include <linux/vga_switcheroo.h>
>
> #include <drm/drm_crtc.h>
> #include <drm/drm_fb_helper.h>
> @@ -337,7 +336,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
> ifbdev->vma_flags = flags;
>
> intel_runtime_pm_put(&dev_priv->runtime_pm, wakeref);
> - vga_switcheroo_client_fb_set(pdev, info);
> return 0;
>
> out_unpin:
> diff --git a/drivers/gpu/drm/radeon/radeon_fbdev.c b/drivers/gpu/drm/radeon/radeon_fbdev.c
> index fb70de29545c6..730efabe05f6b 100644
> --- a/drivers/gpu/drm/radeon/radeon_fbdev.c
> +++ b/drivers/gpu/drm/radeon/radeon_fbdev.c
> @@ -303,7 +303,6 @@ static void radeon_fbdev_client_unregister(struct drm_client_dev *client)
> 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 {
> @@ -342,8 +341,6 @@ static int radeon_fbdev_client_hotplug(struct drm_client_dev *client)
> 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:
> diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> index 79525ee90e3b2..57b21b6869231 100644
> --- a/drivers/video/fbdev/core/fbcon.c
> +++ b/drivers/video/fbdev/core/fbcon.c
> @@ -64,6 +64,7 @@
> #include <linux/console.h>
> #include <linux/string.h>
> #include <linux/kd.h>
> +#include <linux/pci.h>
> #include <linux/slab.h>
> #include <linux/fb.h>
> #include <linux/fbcon.h>
> @@ -75,6 +76,7 @@
> #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"
> @@ -2909,6 +2911,9 @@ void fbcon_fb_unregistered(struct fb_info *info)
>
> console_lock();
>
> + if (info->device && dev_is_pci(info->device))
> + vga_switcheroo_client_fb_set(to_pci_dev(info->device), info);
> +
> fbcon_registered_fb[info->node] = NULL;
> fbcon_num_registered_fb--;
>
> @@ -3042,6 +3047,10 @@ static int do_fb_registered(struct fb_info *info)
> }
> }
>
> + /* 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), NULL);
> +
> 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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2026-01-20 8:13 ` [PATCH 1/2] drm, fbcon, vga_switcheroo: Avoid race condition in fbcon setup Thomas Zimmermann
2026-01-20 8:20 ` Thomas Zimmermann
[not found] <20260120082841.11381-1-tzimmermann@suse.com>
2026-01-20 8:28 ` Thomas Zimmermann
2026-01-20 8:29 ` Thomas Zimmermann
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