Re: [Xen-devel] [PATCH 5/7] xen: Make event channel work with PV extension of HVM

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 03/01/2010 09:48 PM, Sheng Yang wrote:
> > Presumably even if we don't have PV_EVTCHN available/enabled, the Xen
> > clocksource would be available for getting time?
> >      
> I think currently Xen pv clocksource and clockevent are binding... Not sure if
> a single line "clocksource_register(&xen_clocksource)" can work. I would give
> it a try, maybe add a new PV feature.
>    
There should be no strong binding between them, but there may be some 
sloppy assumptions in xen/time.c which should be fixed.  Linux itself 
treats clocksources and eventsources as completely distinct entities, 
and doesn't assume they're running on the same timebase (for example).
Having a PV clocksource even if the timer interrupts are emulated would 
make sense and be useful.
> > >         xen_setup_vcpu_info_placement();
> > >    }
> > > @@ -480,3 +487,138 @@ void __init xen_smp_init(void)
> > >         xen_fill_possible_map();
> > >         xen_init_spinlocks();
> > >    }
> > > +
> > > +static __cpuinit void xen_hvm_pv_start_secondary(void)
> > > +{
> > > +       int cpu = smp_processor_id();
> > > +
> > > +       cpu_init();
> > > +       touch_nmi_watchdog();
> > > +       preempt_disable();
> > > +
> > > +       /* otherwise gcc will move up smp_processor_id before the cpu_init */
> > > +       barrier();
> > > +       /*
> > > +        * Check TSC synchronization with the BSP:
> > > +        */
> > > +       check_tsc_sync_target();
> > > +
> > > +       /* Done in smp_callin(), move it here */
> > > +       set_mtrr_aps_delayed_init();
> > > +       smp_store_cpu_info(cpu);
> > > +
> > > +       /* This must be done before setting cpu_online_mask */
> > > +       set_cpu_sibling_map(cpu);
> > > +       wmb();
> > > +
> > > +       set_cpu_online(smp_processor_id(), true);
> > > +       per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE;
> > > +
> > > +       /* enable local interrupts */
> > > +       local_irq_enable();
> > > +
> > > +       xen_setup_cpu_clockevents();
> > >        
> > How much of this is necessary?  At this point, isn't CPU bringup the
> > same as PV?
> >      
> Xen_enable_sysenter/syscall is not needed for this. And we have a TSC sync
> here - but it seems unnecessary for PV. But set_mtrr_aps_delayed_init() is
> needed. Reuse the cpu_bring_up() is fine?
>    
Doesn't Xen arrange for the tscs to be synced anyway?

> > Is the MMUEXT_TLB_FLUSH/INVLPG_MULTI hypercall not currently available
> > to HVM?
> >      
> I think they are different. These hypercalls flushed native's TLB, but HVM
> want to flush guest one, especially when using shadow, HVM need do something
> for it.
>    
I see.

    J

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