Re: [PATCH 0/8] use jump labels to streamline common APIC configuration

[Gleb Natapov <gleb@redhat.com>]

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.

--
			Gleb.