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Re: [PATCH v2 1/8] x86/xen/pv: Don't setup runstate area too early
- To: Teddy Astie <teddy.astie@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Fri, 16 Oct 2026 19:04:23 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>, David Woodhouse <dwmw2@xxxxxxxxxxxxx>, x86@xxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
- Delivery-date: Fri, 16 Oct 2026 18:04:52 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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
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