On Sun, Aug 05, 2012 at 05:00:37PM +0300, Avi Kivity wrote: > On 08/05/2012 04:48 PM, Gleb Natapov wrote: > >> > >> >> During guest boot up, some of these jump keys will change, no? Does > >> >> this mean a stop_machine() or equivalent? I'm worried about real-time > >> >> response or one guest being affected by another. > >> >> > >> > Yes, SW enable bit changes during boot. The jump label triggerable by a > >> > guest are rate limited though. So stop machine will not happen more then > >> > once per second even with malicious guests. > >> > >> I'm not talking about a malicious guest, just a guest that is booting up > >> normally but kills real-time response for another guest (or just induces > >> a large hiccup in a non-real-time guest, but we don't guarantee anything > >> for those). > >> > >> We don't support real-time guests now, but Jan has plans. > >> > > For such setup jump labels have to be compiled out from the kernel > > completely. Anything that calls stop_machine does not play well with > > real time. > > > > Guest can cause stop machine on boot today already by detecting PMU and > > configuring NMI watchdog. > > The host can prevent this by leaving disabling the guest pmu. But > disabling jump labels for real-time kernels may be acceptable too. We > can probably to it at run time by forcing the slow path at all times. Yes, it is possible to add module option that will force slow path if needed. -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
