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

[Sneh Mankad <sneh.mankad@oss.qualcomm.com>]

On 23-Jun-26 5:10 PM, Daniel Lezcano wrote:
> 
> Hi Sned,
> 
> On 6/5/26 12:30, 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.
> 
> What is the status of this change ? Are you planning to send a new version with the check inside arch_cpu_is_hotpluggable() ?

Yes Daniel, I am sending v2 with adding the check in arm64 specific file.

Thanks,
Sneh
> 
>> Signed-off-by: Sneh Mankad <sneh.mankad@oss.qualcomm.com>
>> ---
>>   kernel/cpu.c         | 4 ++++
>>   kernel/power/Kconfig | 8 ++++++++
>>   2 files changed, 12 insertions(+)
>>
>> diff --git a/kernel/cpu.c b/kernel/cpu.c
>> index bc4f7a9ba64e62d76fbb2b362f243c918defe5bc..1c878db1d9cb6df0e31cb55343851aab4e38a3a0 100644
>> --- a/kernel/cpu.c
>> +++ b/kernel/cpu.c
>> @@ -1478,6 +1478,10 @@ static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
>>        */
>>       if (cpu_hotplug_offline_disabled)
>>           return -EOPNOTSUPP;
>> +#ifdef CONFIG_PM_SLEEP_SMP_CPU_ZERO_STRICT
>> +    if (cpu == get_boot_cpu_id())
>> +        return -EPERM;
>> +#endif
>>       if (cpu_hotplug_disabled)
>>           return -EBUSY;
>>       return _cpu_down(cpu, 0, target);
>> diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
>> index 05337f437cca29da57864583166d7f9abd526507..0b342b3a4a5650a1927dc4805d1515e1d9e067c6 100644
>> --- a/kernel/power/Kconfig
>> +++ b/kernel/power/Kconfig
>> @@ -401,3 +401,11 @@ config ENERGY_MODEL
>>         The exact usage of the energy model is subsystem-dependent.
>>           If in doubt, say N.
>> +
>> +config PM_SLEEP_SMP_CPU_ZERO_STRICT
>> +    bool "Disallow boot CPU (CPU0) offline"
>> +    depends on HOTPLUG_CPU
>> +    depends on SUSPEND
>> +    help
>> +      Disallow boot CPU (CPU0) offline when the suspend_ops->enter()
>> +      has to be executed by boot CPU.
>>
>> ---
>> base-commit: ba3e43a9e601636f5edb54e259a74f96ca3b8fd8
>> change-id: 20260603-disable_boot_cpu_offline-eb4f55ac96f2
>>
>> Best regards,
>