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

[Peter Zijlstra]

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.