From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from dan.rpsys.net (5751f4a1.skybroadband.com [87.81.244.161]) by mail.openembedded.org (Postfix) with ESMTP id EFF1E60119 for ; Wed, 9 Mar 2016 21:23:52 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by dan.rpsys.net (8.14.4/8.14.4/Debian-4.1ubuntu1) with ESMTP id u29LNoS1022760; Wed, 9 Mar 2016 21:23:50 GMT Received: from dan.rpsys.net ([127.0.0.1]) by localhost (dan.rpsys.net [127.0.0.1]) (amavisd-new, port 10024) with LMTP id oqOcV-dzEXcv; Wed, 9 Mar 2016 21:23:50 +0000 (GMT) Received: from hex ([192.168.3.34]) (authenticated bits=0) by dan.rpsys.net (8.14.4/8.14.4/Debian-4.1ubuntu1) with ESMTP id u29LNipG022756 (version=TLSv1/SSLv3 cipher=AES128-GCM-SHA256 bits=128 verify=NOT); Wed, 9 Mar 2016 21:23:45 GMT Message-ID: <1457558624.2804.181.camel@linuxfoundation.org> From: Richard Purdie To: Bruce Ashfield , Paul Gortmaker Date: Wed, 09 Mar 2016 21:23:44 +0000 In-Reply-To: <56E07128.2060401@windriver.com> References: <2e6d2b75837731be983d888eaa82a9cfcf660e85.1455203562.git.bruce.ashfield@windriver.com> <1455287765.16142.321.camel@linuxfoundation.org> <1455291157.16142.323.camel@linuxfoundation.org> <1455352317.16142.344.camel@linuxfoundation.org> <1455383832.16142.365.camel@linuxfoundation.org> <20160302014146.GE20979@windriver.com> <56E07128.2060401@windriver.com> X-Mailer: Evolution 3.16.5-1ubuntu3.1 Mime-Version: 1.0 Cc: "Hart, Darren" , "saul.wold" , poky@yoctoproject.org, openembedded-core Subject: Re: [poky] [PATCH 1/1] poky: update qemu* to prefer 4.4 kernel X-BeenThere: openembedded-core@lists.openembedded.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Patches and discussions about the oe-core layer List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 09 Mar 2016 21:23:54 -0000 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit On Wed, 2016-03-09 at 13:53 -0500, Bruce Ashfield wrote: > On 2016-03-01 8:41 PM, Paul Gortmaker wrote: > > [Re: [poky] [PATCH 1/1] poky: update qemu* to prefer 4.4 kernel] On > > 13/02/2016 (Sat 17:17) Richard Purdie wrote: > > > > > I'm moving the discussion to OE-Core and pulling in some kernel > > > people. > > > I think I understand what is wrong and how to fix it but I could > > > use > > > someone who actually knows this code. > > > > > > To summarise the story so far, on qemux86, X doesn't start and > > > there is > > > a backtrace in the logs: > > > > > > x86/PAT: Xorg:705 map pfn expected mapping type uncached-minus > > > for [mem 0xfd000000-0xfdffffff], got write-combining > > > > So Bruce helped me set up a reproducer locally today since he'd > > already > > invested the time on that, and then I boiled that down to divorce > > it > > from the slower steps of build-deploy-boot to make the bisect > > something > > that mortal humans could tolerate. > > > > Amusingly enough that led to: > > > > commit 9cd25aac1f44f269de5ecea11f7d927f37f1d01c > > Author: Borislav Petkov > > Date: Thu Jun 4 18:55:10 2015 +0200 > > > > x86/mm/pat: Emulate PAT when it is disabled > > > > So while some of us were joking on IRC about the validity of > > forcibly > > disabling PAT (via cmdline or Kconfig) as a workaround, the one > > line > > shortlog above tells us that it wasn't so off the mark after all. > > > > Bruce and I will decide what to do with this tomorrow, but since > > Richard > > spent so much time on it, I thought he'd like to know this in the > > interim. Good times. :-/ > > As another follow up. The thread can be summarized as "It doesn't > look like it should have worked before, and qemu's pat emulation > may be the issue'. > > The suggestion is to run with 'nopat', which is what Richard > originally > did. > > So I'm going to prep a patch that drops the kernel patch, and leaves > nopat enabled on the qemu command line. That should get us put back > together in a semi-permanent way. How sure are we this is a bug in QEMU's pat emulation? If that is the case we should file a bug against qemu and try and fix it rather than work around it... Cheers, Richard