Re: cpu hotplug

[Gleb Natapov <gleb@redhat.com>]

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.