Message-ID: <4F4DF913.5030809@redhat.com>
Date: Wed, 29 Feb 2012 12:08:19 +0200
From: Avi Kivity <avi@redhat.com>
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To: Gleb Natapov <gleb@redhat.com>
CC: Wen Congyang <wency@cn.fujitsu.com>, kvm list <kvm@vger.kernel.org>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        "Daniel P. Berrange" <berrange@redhat.com>,
        linux-kernel@vger.kernel.org, qemu-devel <qemu-devel@nongnu.org>
Subject: Re: [PATCH] kvm: notify host when guest paniced
References: <4F4AF1FB.6000903@cn.fujitsu.com> <4F4CB926.6050600@redhat.com> <4F4D7F5E.5040202@cn.fujitsu.com> <4F4DF4C6.90609@redhat.com> <20120229095557.GE24600@redhat.com> <4F4DF749.7060507@redhat.com> <20120229100550.GF24600@redhat.com>
In-Reply-To: <20120229100550.GF24600@redhat.com>
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On 02/29/2012 12:05 PM, Gleb Natapov wrote:
> On Wed, Feb 29, 2012 at 12:00:41PM +0200, Avi Kivity wrote:
> > On 02/29/2012 11:55 AM, Gleb Natapov wrote:
> > > > >
> > > > 
> > > > How about using a virtio-serial channel for this?  You can transfer any
> > > > amount of information (including the dump itself).
> > > > 
> > > Isn't it unreliable after the guest panicked? 
> > 
> > So is calling hypercalls, or dumping, or writing to the screen.  Of
> > course calling a hypercall is simpler and so is more reliable.
> > 
> Yes, crash can be so severe that it is not even detected by a kernel
> itself, so not OOPS message even printed. But in most cases if kernel is
> functional enough to print OOPS it is functional enough to call single
> hypercall instruction.

Why not print the oops to virtio-serial?  Or even just a regular serial
port?  That's what bare metal does.

> > > Having special kdump
> > > kernel that transfers dump to a host via virtio-serial channel though
> > > sounds interesting. May be that's what you mean.
> > 
> > Yes.  The "panic, starting dump" signal should be initiated by the
> > panicking kernel though, in case the dump fails.
> > 
> Then panic hypercall sounds like a reasonable solution.

It is, but I'm trying to see if we can get away with doing nothing.

-- 
error compiling committee.c: too many arguments to function

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