Re: [PATCH v2 1/8] x86/xen/pv: Don't setup runstate area too early

[Teddy Astie]

Le 16/10/2026 à 20:04, Andrew Cooper a écrit :
> On 16/10/2026 6:33 pm, Andrew Cooper wrote:
> > On 16/10/2026 6:06 pm, Teddy Astie wrote:
> > > This is no longer required since [1].
> > >
> > > At this moment of boot, per_cpu areas are not initialized, which prevents
> > > using VCPUOP_register_runstate_phys_area as per_cpu_ptr_to_phys() would
> > > misbehave in this case.
> > This isn't really correct.
> >
> > The per-cpu area for the BSP is within the main image, which is why the
> > logic functions today.  What's missing is the call to
> > pcpu_setup_first_chunk() which tells per_cpu_ptr_to_phys() about where
> > the BSP data is.
> >
> > I think you want to say:
> >
> > "A future change wants to use per_cpu_ptr_to_phys() in
> > xen_setup_runstate_info(), but this call is too early.  It turns out to
> > be no longer required since ..."
> >
> > > [1] 8a22b9996b00 ("xen: drop xen_sched_clock in favour of using plain wallclock time")
> > > ---
> > Missing SoB.
> >
> > ~Andrew
>
> But this does pose another question...   Linux only ever registers time
> referencing vCPU 0.  Why are the targets of the registration in the
> per-cpu area?  That's presumably wasted space on all APs.

Yes but only for this early PV case, there are other places where 
xen_setup_runstate_info() is called for other APs.

But looking at it, there may be redundant calls of 
xen_setup_runstate_info().

> ~Andrew

Teddy

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