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Tue, 2 Dec 2025 07:42:52 +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 C5bhOHyYLmnQAQAAD6G6ig (envelope-from ); Tue, 02 Dec 2025 07:42:52 +0000 Message-ID: <250b44b3-e75b-4f8d-af44-d3a985ea554c@suse.de> Date: Tue, 2 Dec 2025 08:42:52 +0100 Precedence: bulk X-Mailing-List: linux-fbdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 6.6.y] drm, fbcon, vga_switcheroo: Avoid race condition in fbcon setup To: Sasha Levin , stable@vger.kernel.org Cc: Javier Martinez Canillas , Alex Deucher , dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, linux-fbdev@vger.kernel.org References: <2025120119-quake-universal-d896@gregkh> <20251201225123.1298682-1-sashal@kernel.org> Content-Language: en-US From: Thomas Zimmermann Autocrypt: addr=tzimmermann@suse.de; keydata= xsBNBFs50uABCADEHPidWt974CaxBVbrIBwqcq/WURinJ3+2WlIrKWspiP83vfZKaXhFYsdg XH47fDVbPPj+d6tQrw5lPQCyqjwrCPYnq3WlIBnGPJ4/jreTL6V+qfKRDlGLWFjZcsrPJGE0 BeB5BbqP5erN1qylK9i3gPoQjXGhpBpQYwRrEyQyjuvk+Ev0K1Jc5tVDeJAuau3TGNgah4Yc hdHm3bkPjz9EErV85RwvImQ1dptvx6s7xzwXTgGAsaYZsL8WCwDaTuqFa1d1jjlaxg6+tZsB 9GluwvIhSezPgnEmimZDkGnZRRSFiGP8yjqTjjWuf0bSj5rUnTGiyLyRZRNGcXmu6hjlABEB AAHNJ1Rob21hcyBaaW1tZXJtYW5uIDx0emltbWVybWFubkBzdXNlLmRlPsLAjgQTAQgAOAIb AwULCQgHAgYVCgkICwIEFgIDAQIeAQIXgBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftODH AAoJEGgNwR1TC3ojx1wH/0hKGWugiqDgLNXLRD/4TfHBEKmxIrmfu9Z5t7vwUKfwhFL6hqvo lXPJJKQpQ2z8+X2vZm/slsLn7J1yjrOsoJhKABDi+3QWWSGkaGwRJAdPVVyJMfJRNNNIKwVb U6B1BkX2XDKDGffF4TxlOpSQzdtNI/9gleOoUA8+jy8knnDYzjBNOZqLG2FuTdicBXblz0Mf vg41gd9kCwYXDnD91rJU8tzylXv03E75NCaTxTM+FBXPmsAVYQ4GYhhgFt8S2UWMoaaABLDe 7l5FdnLdDEcbmd8uLU2CaG4W2cLrUaI4jz2XbkcPQkqTQ3EB67hYkjiEE6Zy3ggOitiQGcqp j//OwE0EWznS4AEIAMYmP4M/V+T5RY5at/g7rUdNsLhWv1APYrh9RQefODYHrNRHUE9eosYb T6XMryR9hT8XlGOYRwKWwiQBoWSDiTMo/Xi29jUnn4BXfI2px2DTXwc22LKtLAgTRjP+qbU6 3Y0xnQN29UGDbYgyyK51DW3H0If2a3JNsheAAK+Xc9baj0LGIc8T9uiEWHBnCH+RdhgATnWW GKdDegUR5BkDfDg5O/FISymJBHx2Dyoklv5g4BzkgqTqwmaYzsl8UxZKvbaxq0zbehDda8lv hFXodNFMAgTLJlLuDYOGLK2AwbrS3Sp0AEbkpdJBb44qVlGm5bApZouHeJ/+n+7r12+lqdsA EQEAAcLAdgQYAQgAIAIbDBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftOH6AAoJEGgNwR1T C3ojVSkIALpAPkIJPQoURPb1VWjh34l0HlglmYHvZszJWTXYwavHR8+k6Baa6H7ufXNQtThR yIxJrQLW6rV5lm7TjhffEhxVCn37+cg0zZ3j7zIsSS0rx/aMwi6VhFJA5hfn3T0TtrijKP4A SAQO9xD1Zk9/61JWk8OysuIh7MXkl0fxbRKWE93XeQBhIJHQfnc+YBLprdnxR446Sh8Wn/2D Ya8cavuWf2zrB6cZurs048xe0UbSW5AOSo4V9M0jzYI4nZqTmPxYyXbm30Kvmz0rYVRaitYJ 4kyYYMhuULvrJDMjZRvaNe52tkKAvMevcGdt38H4KSVXAylqyQOW5zvPc4/sq9c= In-Reply-To: <20251201225123.1298682-1-sashal@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spamd-Result: default: False [-4.27 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.17)[-0.858]; MIME_GOOD(-0.10)[text/plain]; MIME_TRACE(0.00)[0:+]; TO_MATCH_ENVRCPT_ALL(0.00)[]; ARC_NA(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_TLS_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; RCPT_COUNT_SEVEN(0.00)[8]; MID_RHS_MATCH_FROM(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[amd.com:email,lists.freedesktop.org:email,suse.de:mid,suse.de:email,msgid.link:url,bootlin.com:url,suse.com:url] X-Spam-Level: X-Spam-Flag: NO X-Spam-Score: -4.27 Hi, thanks for backporting. You also have to remove the calls to vga_switcheroo_client_fb_set() from these files https://elixir.bootlin.com/linux/v6.6/source/drivers/gpu/drm/i915/display/intel_fbdev.c https://elixir.bootlin.com/linux/v6.6/source/drivers/gpu/drm/radeon/radeon_fbdev.c Best regards Thomas Am 01.12.25 um 23:51 schrieb Sasha Levin: > From: Thomas Zimmermann > > [ 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 > 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 > [ drm_fb_helper_unregister_info() lacks vga_switcheroo code ] > Signed-off-by: Sasha Levin > --- > drivers/gpu/drm/drm_fb_helper.c | 7 ------- > drivers/video/fbdev/core/fbcon.c | 9 +++++++++ > 2 files changed, 9 insertions(+), 7 deletions(-) > > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c > index b507c1c008a3e..3891837a78414 100644 > --- 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 > -#include > #include > -#include > > #include > #include > @@ -1668,7 +1666,6 @@ 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 +1684,6 @@ 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/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c > index 78a5b22c8d150..8b2c3065c0c26 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" > @@ -2913,6 +2915,9 @@ 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), NULL); > + > fbcon_registered_fb[info->node] = NULL; > fbcon_num_registered_fb--; > > @@ -3046,6 +3051,10 @@ 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), 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)