Re: [Xen-devel] [PATCH][v9 4/6] xen/hvm: Xen PV extension of HVMinitialization

[Jeremy Fitzhardinge]

On 03/15/2010 06:51 PM, Sheng Yang wrote:
> On Tuesday 16 March 2010 06:59:58 Jeremy Fitzhardinge wrote:
>    
> > On 03/15/2010 05:04 AM, Stefano Stabellini wrote:
> >      
> > > > But we should make sure Xen have ability to support such kind of
> > > > operation. The CPUID would show if Xen have such ability, and if it
> > > > does, the feature would be enabled unconditionally. Guest kernel always
> > > > enable all features it can do unconditionally, but Xen should offer the
> > > > support for them.
> > > >          
> > > In my opinion once the guest knows that is running on Xen HVM (that is
> > > from xen_cpuid_base() or xen_para_available()) it should assume
> > > that the pv clocksource is available, therefore XEN_HVM_PV_CLOCK_ENABLED
> > > should not be needed.
> > > In other words the mere presence of Xen should imply
> > > XEN_HVM_PV_CLOCK_ENABLED.
> > >        
> > The only reason why we wouldn't want to do this is if we want to
> > withdraw this feature at some point in the future.  We're stuck with it
> > indefinitely for PV, but I don't know if that's necessarily going to be
> > the case for HVM.  On the other hand, if other - better - mechanisms
> > become available, we can give them their own clocksource driver with a
> > higher priority than the Xen pvclock one, and users can still select
> > clocksources on the kernel command line.
> >      
> So you think about adding a new XENFEAT?
>    

I think that's a bit arbitrary.  If we need a new vcpuop to make it work 
properly anyway (set tsc offset), then the presence of that should be a 
good indicator.  In other words, make it depend on its actual fixed 
pre-reqs, rather than a specific flag for the feature.

> > Seems like making it work for both 32 and 64-bit is the easiest thing to
> >   do.
> >      
> If it is, it should be fine. But I had encountered some issues on 32 bits.
>    

What kinds of issues?

    J
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/