Re: [PATCH] kernel/cpu: Disallow offlining boot CPU based on config

[Daniel Lezcano]

Hi Thomas,

Le 05/06/2026 à 14:20, Thomas Gleixner a écrit :
> On Fri, Jun 05 2026 at 12:43, Peter Zijlstra wrote:
>
> > On Fri, Jun 05, 2026 at 04:00:46PM +0530, Sneh Mankad wrote:
> > > The Qualcomm SoCs like LeMans, Monaco support suspend to ram which leads
> > > the SoC to ACPI S3 similar state where SoC is turned off and DDR is
> > > retained.
> > > The hardware design on these SoCs forces a constraint to suspend and
> > > resume the system on boot CPU / CPU0.
> > >
> > > If CPU0 is already offline before starting suspend to ram the
> > > freeze_secondary_cpus() picks alternate CPU as primary / last CPU and
> > > proceed further to invoke PSCI SYSTEM_SUSPEND.
> > > This leads to a system crash.
> > >
> > > In order to prevent such an issue introduce PM_SLEEP_SMP_CPU_ZERO_STRICT
> > > config and when enabled prohibit the CPU0 to be offline.
> >
> > Why do this in generic code? Why can't this live in arch code.
> > Specifically, x86 can't typically unplug CPU0 at all either.
>
> arch_cpu_is_hotpluggable(cpu) provides that info to the cpu device core.
>
> No hackery in cpu.c required at all.

Ah, thanks for pointing this out !