On Sun, Aug 05, 2012 at 04:42:17PM +0300, Avi Kivity wrote: > On 08/05/2012 04:35 PM, Gleb Natapov wrote: > > On Sun, Aug 05, 2012 at 04:33:02PM +0300, Avi Kivity wrote: > >> On 08/05/2012 03:58 PM, Gleb Natapov wrote: > >> > APIC code has a lot of checks for apic presence and apic HW/SW enable > >> > state. Most common configuration is when each vcpu has in kernel apic > >> > and it is fully enabled. This path series uses jump labels to turn checks > >> > to nops in the common case. > >> > > >> > Gleb Natapov (8): > >> > KVM: clean up kvm_(set|get)_apic_base > >> > KVM: use kvm_lapic_set_base() to change apic_base > >> > KVM: mark apic enabled on start up. > >> > Export jump_label_rate_limit() > >> > KVM: use jump label to optimize checking for HW enabled APIC in > >> > APIC_BASE MSR. > >> > KVM: use jump label to optimize checking for SW enabled apic in > >> > spurious interrupt register > >> > KVM: use jump label to optimize checking for in kernel local apic > >> > presence. > >> > KVM: inline kvm_apic_present() and kvm_lapic_enabled() > >> > >> Neat. > >> > >> 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. -- 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
