From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 29274CA0EE0 for ; Wed, 13 Aug 2025 12:10:44 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1umAIR-0001W5-MH; Wed, 13 Aug 2025 08:09:35 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1um7RA-0008VP-U1 for qemu-devel@nongnu.org; Wed, 13 Aug 2025 05:06:24 -0400 Received: from smtp-out1.suse.de ([195.135.223.130]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1um7R8-0006Wq-Dd for qemu-devel@nongnu.org; Wed, 13 Aug 2025 05:06:24 -0400 Received: from imap1.dmz-prg2.suse.org (unknown [10.150.64.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id D11E1219BE; Wed, 13 Aug 2025 09:06:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1755075979; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=wzPfss0Yx81jm9T9+iN5ZthUeT7U2XD4wjBOjc1Dsnw=; b=Gw4A60S0hTXkXfeFH2xcZAMc40qN3iZr9CcHEx9ycD3OnUKHU4DmqHwHcy4aP6CurW/uMK CGpS4frnBZxw5OFue9T7hgZjGoxPCKloSdhn9rkQ9hPnJgtBrrrKSUGAPo4wDi/50F1/g6 aD8K/qYaU3fgaM5zkrzcUfStMbv0XcY= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1755075979; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=wzPfss0Yx81jm9T9+iN5ZthUeT7U2XD4wjBOjc1Dsnw=; b=RVhlVVVYaOE6dzETfyqdm4YXHqLJWpSw2caDrnnYjJ9+Jn4w3H6fwWiOLLo3Sz05YdhXxM G5NJ+Htttui+sVCw== Authentication-Results: smtp-out1.suse.de; none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1755075978; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=wzPfss0Yx81jm9T9+iN5ZthUeT7U2XD4wjBOjc1Dsnw=; b=topybgz3V4ZL1tf3jXFyvDYIqy+rSBo669MRUOv4KK6GRFVqMTsY2NFBMZBgjYWk8EuxH2 Gg304KAH1NouwSpMtAd+5VH72pAgYxePiUrhdo1p5nlKmmfi6/muFt63+6kskkLkrDfUfY i9kspoWq+tUsAFeAYz0LQu0moijhTQM= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1755075978; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=wzPfss0Yx81jm9T9+iN5ZthUeT7U2XD4wjBOjc1Dsnw=; b=9B5FwsJlCcAx0wZ1G7OnXQAFvXyQ1xD8YM0oj6V7YHq+sM1HVRqCBS4nVL1r4Bvig8fO7m VRxjDReqRvc50kBg== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 780A113479; Wed, 13 Aug 2025 09:06:18 +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 NVOzG4pVnGhEFAAAD6G6ig (envelope-from ); Wed, 13 Aug 2025 09:06:18 +0000 Message-ID: Date: Wed, 13 Aug 2025 11:06:18 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [REGRESSION][BISECTED] kernel panic is not displayed correctly in qemu (CONFIG_DRM_BOCHS) To: Askar Safin Cc: Gerd Hoffmann , =?UTF-8?Q?Noralf_Tr=C3=B8nnes?= , Maarten Lankhorst , Maxime Ripard , virtualization , ryasuoka , dri-devel , qemu-devel , regressions , Ben Hutchings References: <197f290e30b.eaadc7bc7913.7315623184036672946@zohomail.com> 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: <197f290e30b.eaadc7bc7913.7315623184036672946@zohomail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-0.998]; MIME_GOOD(-0.10)[text/plain]; ARC_NA(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; TO_DN_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; RCVD_TLS_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_COUNT_TWO(0.00)[2]; RCPT_COUNT_SEVEN(0.00)[11]; MID_RHS_MATCH_FROM(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo, suse.de:mid, suse.de:email] Received-SPF: pass client-ip=195.135.223.130; envelope-from=tzimmermann@suse.de; helo=smtp-out1.suse.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-Mailman-Approved-At: Wed, 13 Aug 2025 08:09:32 -0400 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Hi Am 10.07.25 um 06:21 schrieb Askar Safin: > Steps to reproduce: > > - Build Linux v6.16-rc5 so: > > $ cat mini > CONFIG_64BIT=y > > CONFIG_EXPERT=y > CONFIG_EMBEDDED=y > > CONFIG_PRINTK=y > CONFIG_PRINTK_TIME=y > > CONFIG_PCI=y > > CONFIG_TTY=y > CONFIG_VT=y > CONFIG_VT_CONSOLE=y > CONFIG_DRM=y > CONFIG_DRM_FBDEV_EMULATION=y > CONFIG_DRM_BOCHS=y > CONFIG_FRAMEBUFFER_CONSOLE=y > CONFIG_PROC_FS=y > $ make KCONFIG_ALLCONFIG=mini allnoconfig > $ make > > - Then boot this Linux image in Qemu so: > > $ qemu-system-x86_64 -enable-kvm -m 1024 -daemonize -kernel arch/x86_64/boot/bzImage > > Kernel will (predictably) panic (because it has no initramfs, nor real disk), but actual panic message will not be shown! > > Last shown line is "Run /bin/sh as init process" > > My host OS is Debian Trixie. "uname -a": > > Linux receipt 6.12.33+deb13-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.12.33-1 (2025-06-19) x86_64 GNU/Linux > > Qemu version is: > > QEMU emulator version 10.0.2 (Debian 1:10.0.2+ds-1) > > Guest kernel is v6.16-rc5 x86_64. > > The problem doesn't reproduce on old guest kernels. I. e. old guest kernels actually show panic message. > > I did bisect, and bisect showed the following two commits: > > === > > commit a6c3464f69cf5a8a31eb31cc436e7dbd325b8ff9 > Author: Thomas Zimmermann > Date: Thu Jun 13 09:30:33 2019 +0200 > > drm/gem-vram: Support pinning buffers to current location > > Pinning a buffer prevents it from being moved to a different memory > location. For some operations, such as buffer updates, it is not > important where the buffer is located. Setting the pin function's > pl_flag argument to 0 will pin the buffer to whereever it is stored. > > v2: > * document pin flags in PRIME pin helper > > Signed-off-by: Thomas Zimmermann > Acked-by: Gerd Hoffmann > Link: https://patchwork.freedesktop.org/patch/msgid/20190613073041.29350-2-tzimmermann@suse.de > > commit 58540594570778fd149cd8c9b2bff61f2cefa8c9 > Author: Thomas Zimmermann > Date: Wed Jul 3 09:58:34 2019 +0200 > > drm/bochs: Use shadow buffer for bochs framebuffer console > > The bochs driver (and virtual hardware) requires buffer objects to > reside in video ram to display them to the screen. So it can not > display the framebuffer console because the respective buffer object > is permanently pinned in system memory. > > Using a shadow buffer for the console solves this problem. The console > emulation will pin the buffer object only during updates from the shadow > buffer. Otherwise, the bochs driver can freely relocated the buffer > between system memory and video ram. > > v2: > * select shadow FB via struct drm_mode_config.prefer_shadow_fbdev > > Signed-off-by: Thomas Zimmermann > Acked-by: Noralf Trønnes > Link: https://patchwork.freedesktop.org/patch/315833/ > Signed-off-by: Gerd Hoffmann > > === > > Commit a6c3464f69cf5a8a31e changed good behavior to absolutely wrong: after a6c3464f69cf5a8a31e I see just black screen. > Then (after many commits) 58540594570778fd149 made screen working again, but now panics are not shown. > > So, result: all commits in range a6c3464f69cf5a8a31e .. 58540594570778fd149 are not testable (black screen), all commits before a6c3464f69cf5a8a31e > are "good" (panic is shown) and all commits after 58540594570778fd149 (inclusive) (including v6.16-rc5) are "bad" (panic is not shown). The bochs driver uses a shadow framebuffer. It's apparently not being flushed to VRAM on kernel panics. You could try the new DRM panic screen to make that happen. Best regards Thomas > > The next commit after 58540594570778fd149 is 5fd5d2b7c53de5a1290d82, thus correct regzbot instruction is: > > #regzbot introduced: a6c3464f69cf5a8a31e..5fd5d2b7c53de5a1290d82 > > Config above is not special. It is result of minimizing standard Debian config. > > The bug is reproducible with standard Debian kernels (if we use them as guests). > > Reproduction steps are so: > - Install Debian Trixie to Qemu VM > - Boot it with "init=/bin/true" added (to cause kernel panic) > > You will not see panic message. > > I minimized this Debian bug to small config shown in the beginning of this letter. > > -- > Askar Safin > https://types.pl/@safinaskar > -- -- 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)