From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47505) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1did7e-0005H1-CZ for qemu-devel@nongnu.org; Fri, 18 Aug 2017 04:59:19 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1did7a-0002l4-GU for qemu-devel@nongnu.org; Fri, 18 Aug 2017 04:59:18 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33202) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1did7a-0002j6-5Y for qemu-devel@nongnu.org; Fri, 18 Aug 2017 04:59:14 -0400 Date: Fri, 18 Aug 2017 09:59:09 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20170818085908.GB2222@work-vm> References: <8b120ab5-5319-30d6-6971-411c7e5c4330@univention.de> <20170814183910.GA2469@work-vm> <35734e50-0fe7-1809-1826-f6f28856ff88@redhat.com> <410b3398-470f-4434-7488-890054b4921b@univention.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <410b3398-470f-4434-7488-890054b4921b@univention.de> Subject: Re: [Qemu-devel] RFH: difference in read-only mapped bios.bin - memory corruption? List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Philipp Hahn Cc: Laszlo Ersek , qemu-devel@nongnu.org * Philipp Hahn (hahn@univention.de) wrote: > Hello, > > Am 15.08.2017 um 13:25 schrieb Laszlo Ersek: > > On 08/14/17 20:39, Dr. David Alan Gilbert wrote: > >> * Philipp Hahn (hahn@univention.de) wrote: > >>> I'm currently investigating a problem, were a Linux VM does not reboot > >>> and gets stuck in the SeaBIOS reboot code: > >>> > >>> I'm using SeaBIOS-1.7 from Debian with a more modern qemu-2.8 > ...>>> If I dump both regions and compare them, I get a difference: > ...>> You might want seabios commit c68aff5 and b837e6 that got fixed after > >> I tracked down some reboot hangs - although they were rare, not every > >> time. c68aff5 did certainly cause a corruption, and the address of that > >> corruption was determined at link time and could overlay random useful > >> bits of code if you were unlucky. > > Thanks you for the commit IDs - to me this looks like they fixed the > problem. Testing with seabios-1.10 does not show any reboot problem so far. > > >>> 1. How can it be, that the low-mem ROM mapping is modified? > >> > >> I can't remember all the details, but PC ROM is shadowed and mapped over > >> with RAM at various times, > > > > Right. I don't remember for sure, but I believe the state of the PAM > > registers doesn't only affect what the VCPUs see in that address range, > > but also what your monitor commands will dump. (This would be the > > logical choice -- make the monitor output what the VCPUs see anyway, at > > the moment, dependent on the PAM settings.) > > That makes sense. > Do you know by change what change in Qemu triggered that bug, as I've > never seen any reboot problem with qemu-1.1.2, but only since switching > to qemu-2.8? I didn't go back as far as 1.1.2, but I tried bisecting around 2.4/2.6 before I understood the failure and the bisect was very flaky; I think in the end it's a timing race where it comes down to the exact corrupt value; going back to ancient qemu might be taking some other path through seabios but I ddin't investigate. Dave > Thanks again for your excellent help. > > Philipp -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK