Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761218Ab2KAACb (ORCPT ); Wed, 31 Oct 2012 20:02:31 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53812 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761176Ab2KAAC2 (ORCPT ); Wed, 31 Oct 2012 20:02:28 -0400 Date: Wed, 31 Oct 2012 21:15:42 -0200 From: Marcelo Tosatti To: Sasha Levin Cc: Wen Congyang , Hu Tao , kvm list , qemu-devel , "linux-kernel@vger.kernel.org" , Avi Kivity , "Daniel P. Berrange" , KAMEZAWA Hiroyuki , Jan Kiszka , Gleb Natapov , Blue Swirl , Eric Blake , Andrew Jones , Luiz Capitulino Subject: Re: [PATCH v11] kvm: notify host when the guest is panicked Message-ID: <20121031231542.GA20153@amt.cnet> References: <0a2274eccf1b1dd420f16359f7e1de74fa2f9fbe.1351131144.git.hutao@cn.fujitsu.com> <20121031011256.GC12325@amt.cnet> <50908354.5070608@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2624 Lines: 56 On Tue, Oct 30, 2012 at 10:30:02PM -0400, Sasha Levin wrote: > On Tue, Oct 30, 2012 at 9:48 PM, Wen Congyang wrote: > > At 10/31/2012 09:12 AM, Marcelo Tosatti Wrote: > >> It has been asked earlier why a simple virtio device is not usable > >> for this (with no response IIRC). > > > > 1. We can't use virtio device when the kernel is booting. > > So the issue here is the small window between the point the guest > becomes "self aware" and to the point virtio drivers are loaded, > right? > > I agree that if something happens during that interval, a > "virtio-notifier" driver won't catch that, but anything beyond that is > better done with a virtio driver, so how is the generic infrastructure > added in this patch useful to anything beyond detecting panics in that > initial interval? Asked earlier about quantification of panics in that window (i doubt early panics are that significant for this usecase). netconsole has the same issue: "This module logs kernel printk messages over UDP allowing debugging of problem where disk logging fails and serial consoles are impractical. It can be used either built-in or as a module. As a built-in, netconsole initializes immediately after NIC cards and will bring up the specified interface as soon as possible. While this doesn't allow capture of early kernel panics, it does capture most of the boot process." > > 2. The virtio's driver can be built as a module, and if it is not loaded > > and the kernel is panicked, there is no way to notify the host. > > Even if the suggested virtio-notifier driver is built as a module, it > would get auto-loaded when the guest is booting, so I'm not sure about > this point? > > 3. I/O port is more reliable than virtio device. > > If virtio's driver has some bug, and it cause kernel panicked, we can't > > use it. The I/O port is more reliable because it only depends on notifier > > chain(If we use virtio device, it also depends on notifier chain). > > This is like suggesting that we let KVM emulate virtio-blk on it's > own, parallel to the virtio implementation, so that even if there's a > problem with virtio-blk, KVM can emulate a virtio-blk on it's own. > > Furthermore, why stop at virtio? What if the KVM code has a bug and it > doesn't pass IO properly? Or the x86 code? we still want panic > notifications if that happens... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/