From mboxrd@z Thu Jan  1 00:00:00 1970
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: cpu hotplug
Date: Mon, 20 Sep 2010 08:48:43 +0200
Message-ID: <20100920064843.GD3008@redhat.com>
References: <20100919143611.GW3008@redhat.com>
 <1284909384.9521.228.camel@frechmops.schnuffi.conrad.localdomain>
 <20100919151916.GX3008@redhat.com>
 <1284910638.9521.242.camel@frechmops.schnuffi.conrad.localdomain>
 <20100919154113.GZ3008@redhat.com>
 <1284911040.9521.244.camel@frechmops.schnuffi.conrad.localdomain>
 <20100919155347.GA3008@redhat.com>
 <20100919160451.GA18012@morn.localdomain>
 <1284913473.9521.278.camel@frechmops.schnuffi.conrad.localdomain>
 <20100919215725.GA488@morn.localdomain>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Conrad Wood <linux-kvm@conradwood.net>, kvm@vger.kernel.org
To: "Kevin O'Connor" <kevin@koconnor.net>
Return-path: <kvm-owner@vger.kernel.org>
Received: from mx1.redhat.com ([209.132.183.28]:16740 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1752626Ab0ITGst (ORCPT <rfc822;kvm@vger.kernel.org>);
	Mon, 20 Sep 2010 02:48:49 -0400
Content-Disposition: inline
In-Reply-To: <20100919215725.GA488@morn.localdomain>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

On Sun, Sep 19, 2010 at 05:57:25PM -0400, Kevin O'Connor wrote:
> On Sun, Sep 19, 2010 at 06:24:33PM +0200, Conrad Wood wrote:
> > 
> > a script with my exact steps is below. Result is reproducible.
> > 
> [...]
> > echo "Ejecting CPU #4"
> > echo "cpu_set 4 offline" | nc ${MONITORHOST} ${MONITORPORT} >/dev/null
> > 
> > printInfo
> > 
> > echo "Setting all available cpus to online..."
> > ssh -lroot ${VM} "find /sys/devices/system/cpu/ -type f -path
> > '*/cpu?/online' -exec bash -c \"echo 1 >{}\" \;"
> 
> It's not clear if you can trust your guests or not.  If you can trust
> the guest OS, it should be safe to run:
> 
> echo 1 > /sys/devices/LNXSYSTM:00/LNXSYBUS:00/LNXCPU:xx/eject
> 
> in the guest.  A normal linux guest wont reactivate the cpu after
> that.
> 
You can trust you guest more then you can trust a users of your guest.
It is easy for a user to do echo, it is much harder to modify guest to not
remove /sys entry for un-plugged cpu. 

But I agree that kvm shouldn't allow to reactivate un-plugged cpu even
if it is not destroy it on un-plug.

--
			Gleb.