From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55091) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a3ntF-0002Ot-UN for qemu-devel@nongnu.org; Tue, 01 Dec 2015 11:34:57 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1a3ntE-0002bU-Vn for qemu-devel@nongnu.org; Tue, 01 Dec 2015 11:34:53 -0500 Received: from hall.aurel32.net ([2001:bc8:30d7:100::1]:40530) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a3ntE-0002bQ-QR for qemu-devel@nongnu.org; Tue, 01 Dec 2015 11:34:52 -0500 Date: Tue, 1 Dec 2015 17:34:51 +0100 From: Aurelien Jarno Message-ID: <20151201163451.GC9577@aurel32.net> References: <1448986767-28016-1-git-send-email-rth@twiddle.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] [PATCH for-2.5] tcg: Increase the highwater reservation List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell Cc: QEMU Developers , Richard Henderson On 2015-12-01 16:28, Peter Maydell wrote: > On 1 December 2015 at 16:19, Richard Henderson wrote: > > If there are a lot of guest memory ops in the TB, the amount of > > code generated by tcg_out_tb_finalize could be well more than 1k. > > In the short term, increase the reservation larger than any TB > > seen in practice. > > > > Reported-by: Aurelien Jarno > > Signed-off-by: Richard Henderson > > --- > > > > Reported and discussed with Aurelien on IRC yesterday. This seems > > to be the easiest fix for the upcoming release. I will fix this > > properly (by modifying every backend's finalize routines) for 2.6. > > What would be the result of our hitting this bug? I ask because > there's a report on qemu-discuss about a qemu-i386-on-ARM-host > bug: http://lists.nongnu.org/archive/html/qemu-discuss/2015-11/msg00042.html > and the debug log (http://www.mediafire.com/download/ge611be9vbebbw7/qemu.log) > suggests we're segfaulting in translation on the TB shortly > after we (successfully) translate a TB whose final 'out' size > is 1100 and which has 64 guest writes in it. So I'm wondering > if that's actually the same bug this is fixing... I don't think this is the same bug. The problem happens because the slow path of the softmmu load/store access is written at the end of the TB. In user mode, there is no slow path, so nothing is written at the end. -- Aurelien Jarno GPG: 4096R/1DDD8C9B aurelien@aurel32.net http://www.aurel32.net