Re: [RFC PATCH v2 31/35] arm64: psci: Ignore DENIED CPUs

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Wed, 13 Sep 2023 16:38:19 +0000
James Morse <james.morse@arm.com> wrote:

> From: Jean-Philippe Brucker <jean-philippe@linaro.org>
> 
> When a CPU is marked as disabled, but online capable in the MADT, PSCI
> applies some firmware policy to control when it can be brought online.
> PSCI returns DENIED to a CPU_ON request if this is not currently
> permitted. The OS can learn the current policy from the _STA enabled bit.
> 
> Handle the PSCI DENIED return code gracefully instead of printing an
> error.

Specification reference would be good particularly as it's only been
added as a possibility fairly recently.

> 
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> [ morse: Rewrote commit message ]
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
>  arch/arm64/kernel/psci.c     | 2 +-
>  arch/arm64/kernel/smp.c      | 3 ++-
>  drivers/firmware/psci/psci.c | 2 ++
>  3 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c
> index 29a8e444db83..4fcc0cdd757b 100644
> --- a/arch/arm64/kernel/psci.c
> +++ b/arch/arm64/kernel/psci.c
> @@ -40,7 +40,7 @@ static int cpu_psci_cpu_boot(unsigned int cpu)
>  {
>  	phys_addr_t pa_secondary_entry = __pa_symbol(secondary_entry);
>  	int err = psci_ops.cpu_on(cpu_logical_map(cpu), pa_secondary_entry);
> -	if (err)
> +	if (err && err != -EPROBE_DEFER)

Hmm. EPROBE_DEFER has very specific meaning around driver requesting a retry
when some other bit of the system has finished booting. 
I'm not sure it's a good idea for this use case.  Maybe just keep to EPERM
as psci_to_linux_errno() will return anyway.  Seems valid to me, or
is the requirement to use EPROBE_DEFER coming from further up the stack?



>  		pr_err("failed to boot CPU%d (%d)\n", cpu, err);
>  
>  	return err;
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index 8c8f55721786..e958db987665 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -124,7 +124,8 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
>  	/* Now bring the CPU into our world */
>  	ret = boot_secondary(cpu, idle);
>  	if (ret) {
> -		pr_err("CPU%u: failed to boot: %d\n", cpu, ret);
> +		if (ret != -EPROBE_DEFER)
> +			pr_err("CPU%u: failed to boot: %d\n", cpu, ret);
>  		return ret;
>  	}
>  
> diff --git a/drivers/firmware/psci/psci.c b/drivers/firmware/psci/psci.c
> index d9629ff87861..f7ab3fed3528 100644
> --- a/drivers/firmware/psci/psci.c
> +++ b/drivers/firmware/psci/psci.c
> @@ -218,6 +218,8 @@ static int __psci_cpu_on(u32 fn, unsigned long cpuid, unsigned long entry_point)
>  	int err;
>  
>  	err = invoke_psci_fn(fn, cpuid, entry_point, 0);
> +	if (err == PSCI_RET_DENIED)
> +		return -EPROBE_DEFER;
>  	return psci_to_linux_errno(err);
>  }
>