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

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Message-ID: <89a36ddc-5354-5ee0-2066-11a8d4ae1806@redhat.com>
Date:   Tue, 19 Sep 2023 14:31:04 +1000
From:   Gavin Shan <gshan@...hat.com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        James Morse <james.morse@....com>
Cc:     linux-pm@...r.kernel.org, loongarch@...ts.linux.dev,
        linux-acpi@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, kvmarm@...ts.linux.dev,
        x86@...nel.org, Salil Mehta <salil.mehta@...wei.com>,
        Russell King <linux@...linux.org.uk>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        jianyong.wu@....com, justin.he@....com
Subject: Re: [RFC PATCH v2 31/35] arm64: psci: Ignore DENIED CPUs

On 9/15/23 02:01, Jonathan Cameron wrote:
> On Wed, 13 Sep 2023 16:38:19 +0000
> James Morse <james.morse@....com> wrote:
> 
>> From: Jean-Philippe Brucker <jean-philippe@...aro.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.
> 

https://developer.arm.com/documentation/den0022/f/?lang=en   page-58

It seems DENIED is the best matched indicator.

>>
>> Signed-off-by: Jean-Philippe Brucker <jean-philippe@...aro.org>
>> [ morse: Rewrote commit message ]
>> Signed-off-by: James Morse <james.morse@....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?
> 

I agree with Jonathan that -EPERM from psci_to_linux_errno(DENIED) is
good enough here. Actually, I think we need to bail from bringing up
the CPU once error is raised on psci_ops.cpu_on() and avoid reporting
it as error with help of -EPROBE_DEFER. -EPERM can serve the same
purpose.

> 
> 
>>   		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);
>>   }
>>   

Thanks,
Gavin