From mboxrd@z Thu Jan 1 00:00:00 1970 From: "William Z." Subject: Re: =?utf-8?q?Bug_in_x86_instruction_emulator=3F?= Date: Fri, 20 May 2016 18:44:02 +0200 Message-ID: <098860bec81f5e500738246d9c69fcc7@openmailbox.org> References: <20e259d208b95167bb495a6ed0bf684d@openmailbox.org> <573C4E0A02000078000EC68B@prv-mh.provo.novell.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="=_3387550f3d096c8b430960049f3695e4" Return-path: In-Reply-To: <573C4E0A02000078000EC68B@prv-mh.provo.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xen.org Sender: "Xen-devel" To: Jan Beulich Cc: Andrew Cooper , xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org --=_3387550f3d096c8b430960049f3695e4 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=US-ASCII; format=flowed On 2016-05-18 11:12, Jan Beulich wrote: >>>> On 06.04.16 at 01:38, wrote: >> I'm running Xen 4.6.1 with Alpine Linux 3.3.3 in dom0. In a HVM domU >> with vga="qxl", Xorg will segfault instantly if tried started. >> Multiple >> Linux distros have been tested and Xorg segfaults in all. >> >> Attached are a full backtrace from domU generated by Xorg, and a >> assembler dump of function 'sse2_blt'. > > Just FYI: Looks like I can repro this finally, and it also looks like > at > least for me it isn't an SSE2 instruction that the issue is with. > Instead I'm getting an #UD in the middle of an instruction a few > lines down from the last SSE2 one, which suggests we're having > an issue with sizing instructions (however odd that may seem). > Now that I can repro it, at least I have something to actually > debug ... > > Jan I have patched Xen 4.6.1 with commit 2bb230972c5ddb1ca823f47750b5d46a9d302d0e (x86emul: suppress writeback upon unsuccessful MMX/SSE/AVX insn emulation) and tested with different Linux distros. I can say with confidence that the patch has solved my initial problem as Xorg no longer segfaults when started. Thanks to everyone that has helped with this. However, while testing I have found a new problem. This may not be related to my initial problem or even Xen, but I will try to describe it here as I'm hoping someone can point me in the right direction. Various actions will now raise the CPU usage of Xorg to 100% and freeze the entire X Window System for some time. E.g.: Starting xterm in a window manager or directly from .xinitrc and executing dmesg. This will print a few lines per second while the Xorg CPU usage is 100% and the X Window System is frozen for about 60 seconds until all dmesg output has been printed. I have run 'perf record -g -a sleep 60' while connected via SSH and then executed dmesg in xterm. I have attached a few lines of 'perf report -g' with the first one expanded. I have also run 'strace -p $(pidof Xorg)' while dmesg was running in xterm. The lines I have attached will repeat until all dmesg output has been printed. File descriptor 8 is pointing on '/dev/dri/card0'. Any ideas on what could cause this? 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