Re: [External] Re: [PATCH v9 0/8] Parallel CPU bringup for x86_64

[Usama Arif]

On 21/02/2023 11:42, Oleksandr Natalenko wrote:
> On 21.02.2023 11:47, Usama Arif wrote:
> > On 21/02/2023 10:27, David Woodhouse wrote:
> > > On 21 February 2023 09:49:51 GMT, Oleksandr Natalenko 
> > > <oleksandr@xxxxxxxxxxxxxx> wrote:
> > > > On 21.02.2023 10:06, David Woodhouse wrote:
> > > > > Why does arch/x86/kernel/acpi/sleep.c::x86_acpi_suspend_lowlevel() set
> > > > >
> > > > >      initial_gs = per_cpu_offset(smp_processor_id()) ?
> > > > >
> > > > > Would it not be CPU#0 that comes back up, and should it not get
> > > > > per_cpu_offset(0) ?
> > > >
> > > > Wanna me try `initial_gs = per_cpu_offset(0);` too?
> >
> > I think it might be smp_processor_id() and not 0 incase CPU0 was 
> > offline at the point the system was suspended?
>
> Is it even possible for CPU 0 to be offline, at least on x86?

It is possible on x86 (using BOOTPARAM_HOTPLUG_CPU0), but I just read 
the Kconfig option and it says:

"resume from hibernate or suspend always starts from CPU0.
So hibernate and suspend are prevented if CPU0 is offline."

so I guess switching to 0 should be ok.