linux-kernel - Re: [PATCH v10 17/19] arm64: Kconfig: Enable hotplug CPU on arm64 if ACPI

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Date: Sun, 30 Jun 2024 10:39:04 +1000
From: Gavin Shan <gshan@...hat.com>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
 Catalin Marinas <catalin.marinas@....com>, linux-acpi@...r.kernel.org,
 linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org
Cc: Mark Rutland <mark.rutland@....com>, Thomas Gleixner
 <tglx@...utronix.de>, Peter Zijlstra <peterz@...radead.org>,
 loongarch@...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>,
 Hanjun Guo <guohanjun@...wei.com>, 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
Subject: Re: [PATCH v10 17/19] arm64: Kconfig: Enable hotplug CPU on arm64 if
 ACPI_PROCESSOR is enabled.

Hi Jonathan and Catalin,

On 5/29/24 11:34 PM, Jonathan Cameron wrote:
> In order to move arch_register_cpu() to be called via the same path
> for initially present CPUs described by ACPI and hotplugged CPUs
> ACPI_HOTPLUG_CPU needs to be enabled.
> 
> The protection against invalid IDs in acpi_map_cpu() is needed as
> at least one production BIOS is in the wild which reports entries
> in DSDT (with no _STA method, so assumed enabled and present)
> that don't match MADT.
> 
> Tested-by: Miguel Luis <miguel.luis@...cle.com>
> Reviewed-by: Gavin Shan <gshan@...hat.com>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> ---
>   arch/arm64/Kconfig       |  1 +
>   arch/arm64/kernel/acpi.c | 22 ++++++++++++++++++++++
>   2 files changed, 23 insertions(+)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 5d91259ee7b5..e8f2ef2312db 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -5,6 +5,7 @@ config ARM64
>   	select ACPI_CCA_REQUIRED if ACPI
>   	select ACPI_GENERIC_GSI if ACPI
>   	select ACPI_GTDT if ACPI
> +	select ACPI_HOTPLUG_CPU if ACPI_PROCESSOR

ACPI_HOTPLUG_CPU depends on (ACPI_PROCESSOR && HOTPLUG_CPU). It needs to be:

	select ACPI_HOTPLUG_CPU if ACPI_PROCESSOR && HOTPLUG_CPU

Otherwise, we can have compiling error with the following configurations.

CONFIG_ACPI_PROCESSOR=y
CONFIG_HOTPLUG_CPU=n
CONFIG_ACPI_HOTPLUG_CPU=y

arch/arm64/kernel/smp.c: In function ‘arch_unregister_cpu’:
arch/arm64/kernel/smp.c:563:9: error: implicit declaration of function ‘unregister_cpu’; did you mean ‘register_cpu’? [-Werror=implicit-function-declaration]
   563 |         unregister_cpu(c);
       |         ^~~~~~~~~~~~~~
       |         register_cpu

Since the series has been queued to Catalin's "for-next/vcpu-hotplug" branch, I
guess the easiest way would be to fix it in place with Catalin's help.

Thanks,
Gavin

>   	select ACPI_IORT if ACPI
>   	select ACPI_REDUCED_HARDWARE_ONLY if ACPI
>   	select ACPI_MCFG if (ACPI && PCI)
> diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
> index e0e7b93c16cc..9360ba86678b 100644
> --- a/arch/arm64/kernel/acpi.c
> +++ b/arch/arm64/kernel/acpi.c
> @@ -30,6 +30,7 @@
>   #include <linux/pgtable.h>
>   
>   #include <acpi/ghes.h>
> +#include <acpi/processor.h>
>   #include <asm/cputype.h>
>   #include <asm/cpu_ops.h>
>   #include <asm/daifflags.h>
> @@ -423,6 +424,27 @@ void arch_reserve_mem_area(acpi_physical_address addr, size_t size)
>   	memblock_mark_nomap(addr, size);
>   }
>   
> +#ifdef CONFIG_ACPI_HOTPLUG_CPU
> +int acpi_map_cpu(acpi_handle handle, phys_cpuid_t physid, u32 apci_id,
> +		 int *pcpu)
> +{
> +	/* If an error code is passed in this stub can't fix it */
> +	if (*pcpu < 0) {
> +		pr_warn_once("Unable to map CPU to valid ID\n");
> +		return *pcpu;
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(acpi_map_cpu);
> +
> +int acpi_unmap_cpu(int cpu)
> +{
> +	return 0;
> +}
> +EXPORT_SYMBOL(acpi_unmap_cpu);
> +#endif /* CONFIG_ACPI_HOTPLUG_CPU */
> +
>   #ifdef CONFIG_ACPI_FFH
>   /*
>    * Implements ARM64 specific callbacks to support ACPI FFH Operation Region as