From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: Frame buffer corruptions with KVM >= 2.6.36 Date: Thu, 14 Oct 2010 14:13:37 +0200 Message-ID: <4CB6F3F1.9060409@redhat.com> References: <4CB6B0FB.7080100@web.de> <4CB6F33E.3020009@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm , Takuya Yoshikawa To: Jan Kiszka Return-path: Received: from mx1.redhat.com ([209.132.183.28]:2538 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752968Ab0JNMNp (ORCPT ); Thu, 14 Oct 2010 08:13:45 -0400 In-Reply-To: <4CB6F33E.3020009@siemens.com> Sender: kvm-owner@vger.kernel.org List-ID: On 10/14/2010 02:10 PM, Jan Kiszka wrote: > Am 14.10.2010 09:27, Jan Kiszka wrote: > > Hi, > > > > I'm seeing quite frequent corruptions of the VESA frame buffer with > > Linux guests (vga=0x317) that are starting with KVM kernel modules of > > upcoming 2.6.36 (I'm currently running -rc7). Effects disappears when > > downgrading to kvm-kmod-2.6.35.6. Will see if I can bisect later, but > > maybe someone already has an idea or wants to reproduce (just run > > something like "find /" on one text console and witch to another one - > > text fragments will remain on the screen on every few switches). > > Commit d25f31f488e5f7597c17a3ac7d82074de8138e3b in kvm.git ("KVM: x86: > avoid unnecessary bitmap allocation when memslot is clean") is at least > magnifying the issue. With this patch applied, I can easily trigger > display corruptions when switching between VGA consoles while one of > them is undergoing heavy updates. > > However, I once saw a much smaller inconsistency during my tests even > with a previous revision. Maybe there is a fundamental issue in when and > how the coalesced backlog is replayed, I didn't see any mmio writes to the framebuffer, so I don't think coalescing plays a part here. > and this commit just makes the > corruptions more likely. This may even be a QEMU issue in the cirrus/vga > model (both qemu-kvm and upstream show the effect). > What about -no-kvm? -- error compiling committee.c: too many arguments to function