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

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

[Andrew Cooper]

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

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

[Andrew Cooper]

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.

~Andrew