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Tue, 20 Jan 2026 08:18:56 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 2DYkNnA6b2n1bQAAD6G6ig (envelope-from ); Tue, 20 Jan 2026 08:18:56 +0000 From: Thomas Zimmermann To: kernel-kabi@suse.de Cc: Thomas Zimmermann , Javier Martinez Canillas , Alex Deucher , dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, linux-fbdev@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH 1/2] drm, fbcon, vga_switcheroo: Avoid race condition in fbcon setup Date: Tue, 20 Jan 2026 09:13:37 +0100 Message-ID: <20260120081841.9827-2-tzimmermann@suse.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260120081841.9827-1-tzimmermann@suse.com> References: <20260120081841.9827-1-tzimmermann@suse.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Score: -2.80 X-Spamd-Result: default: False [-2.80 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_CONTAINS_FROM(1.00)[]; R_MISSING_CHARSET(0.50)[]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; TO_MATCH_ENVRCPT_ALL(0.00)[]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; FROM_HAS_DN(0.00)[]; MIME_TRACE(0.00)[0:+]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,bootlin.com:url,suse.com:mid]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCPT_COUNT_SEVEN(0.00)[9]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; DKIM_SIGNED(0.00)[suse.com:s=susede1]; TO_DN_SOME(0.00)[]; RCVD_TLS_ALL(0.00)[] X-Spam-Level: X-Spam-Flag: NO From: Thomas Zimmermann 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 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 Acked-by: Alex Deucher Cc: dri-devel@lists.freedesktop.org Cc: nouveau@lists.freedesktop.org Cc: amd-gfx@lists.freedesktop.org Cc: linux-fbdev@vger.kernel.org Cc: # 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 #include #include -#include #include #include @@ -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 #include #include -#include #include #include @@ -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 #include #include +#include #include #include #include @@ -75,6 +76,7 @@ #include #include /* For counting font checksums */ #include +#include #include #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