linux-kernel - Re: [PATCH v8 12/16] arm64: psci: Ignore DENIED CPUs

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Date: Tue, 30 Apr 2024 14:29:11 +1000
From: Gavin Shan <gshan@...hat.com>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <peterz@...radead.org>,
 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,
 kvmarm@...ts.linux.dev, x86@...nel.org, Russell King
 <linux@...linux.org.uk>, "Rafael J . Wysocki" <rafael@...nel.org>,
 Miguel Luis <miguel.luis@...cle.com>, James Morse <james.morse@....com>,
 Salil Mehta <salil.mehta@...wei.com>,
 Jean-Philippe Brucker <jean-philippe@...aro.org>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Marc Zyngier <maz@...nel.org>, Hanjun Guo <guohanjun@...wei.com>
Cc: Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>, linuxarm@...wei.com,
 justin.he@....com, jianyong.wu@....com,
 Lorenzo Pieralisi <lpieralisi@...nel.org>,
 Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH v8 12/16] arm64: psci: Ignore DENIED CPUs

On 4/26/24 23:51, Jonathan Cameron 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.
> 
> Note the alternatives to the PSCI cpu_boot() callback do not
> return -EPERM so the change in smp.c has no affect.
> 
> See https://developer.arm.com/documentation/den0022/f/?lang=en page 58.
> 
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@...aro.org>
> [ morse: Rewrote commit message ]
> Signed-off-by: James Morse <james.morse@....com>
> Tested-by: Miguel Luis <miguel.luis@...cle.com>
> Tested-by: Vishnu Pajjuri <vishnu@...amperecomputing.com>
> Tested-by: Jianyong Wu <jianyong.wu@....com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> ---
> v8: Note in commit message that the -EPERM guard on the error print
>      only affects PSCI as other options never use this error code.
>      Should they do so in future, that may well indicate that they
>      now support similar refusal to boot.
> ---
>   arch/arm64/kernel/psci.c | 2 +-
>   arch/arm64/kernel/smp.c  | 3 ++-
>   2 files changed, 3 insertions(+), 2 deletions(-)
> 

Thanks for the check and clarification that -EPERM is only sensible
to PSCI. With the clarification:

Reviewed-by: Gavin Shan <gshan@...hat.com>

Thanks,
Gavin