From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Lieven Subject: Re: race between kvm-kmod-3.0 and kvm-kmod-3.3 // was: race condition in qemu-kvm-1.0.1 Date: Mon, 02 Jul 2012 17:57:32 +0200 Message-ID: <4FF1C4EC.8080109@dlhnet.de> References: <4FEB2945.1030607@dlhnet.de> <4FEB3AC6.6010206@web.de> <4FEC1FC9.7050103@dlhnet.de> <4FEC2210.1030005@siemens.com> <4FEC2475.4030202@dlhnet.de> <4FEC2626.90402@dlhnet.de> <4FF1B8A6.2020101@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Jan Kiszka , qemu-devel@nongnu.org, kvm@vger.kernel.org, Gleb Natapov To: Avi Kivity Return-path: Received: from ssl.dlhnet.de ([91.198.192.8]:49648 "EHLO ssl.dlh.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753967Ab2GBP5d (ORCPT ); Mon, 2 Jul 2012 11:57:33 -0400 In-Reply-To: <4FF1B8A6.2020101@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 02.07.2012 17:05, Avi Kivity wrote: > On 06/28/2012 12:38 PM, Peter Lieven wrote: >> does anyone know whats that here in handle_mmio? >> >> /* hack: Red Hat 7.1 generates these weird accesses. */ >> if ((addr> 0xa0000-4&& addr<= 0xa0000)&& kvm_run->mmio.len == 3) >> return 0; >> > Just what it says. There is a 4-byte access to address 0x9ffff. The > first byte lies in RAM, the next three bytes are in mmio. qemu is > geared to power-of-two accesses even though x86 can generate accesses to > any number of bytes between 1 and 8. I just stumbled across the word "hack" in the comment. When the race occurs the CPU is basically reading from 0xa0000 in an endless loop. > It appears that this has happened with your guest. It's not impossible > that it's genuine. > I had a lot to do the last days, but I update our build environment to Ubuntu LTS 12.04 64-bit Server which is based on Linux 3.2.0. I still see the issue. If I use the kvm Module provided with the kernel it is working correctly. If I use kvm-kmod-3.4 with qemu-kvm-1.0.1 (both from sourceforge) I can reproduce the race condition. I will keep you posted when I have more evidence. Thanks, Peter