On Tue, Aug 14, 2012 at 04:00:54PM +0200, Jan Kiszka wrote: > On 2012-08-05 16:03, Gleb Natapov wrote: > > 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. > > Should I write a patch or will you? Having host-side stop_machine due to > such common guest operations is indeed a no-go for RT. > Do we support RT now? The operation are definitely not common. -- 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
