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Date: Wed, 29 Feb 2012 12:05:50 +0200
From: Gleb Natapov <gleb@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] kvm: notify host when guest paniced
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To: Avi Kivity <avi@redhat.com>
Cc: kvm list <kvm@vger.kernel.org>, qemu-devel <qemu-devel@nongnu.org>, linux-kernel@vger.kernel.org, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

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.

> > 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.

--
			Gleb.