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Date:   Thu, 14 Sep 2023 15:31:10 +0100
From:   Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To:     James Morse <james.morse@arm.com>
CC:     <linux-pm@vger.kernel.org>, <loongarch@lists.linux.dev>,
        <linux-acpi@vger.kernel.org>, <linux-arch@vger.kernel.org>,
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        <linux-riscv@lists.infradead.org>, <kvmarm@lists.linux.dev>,
        <x86@kernel.org>, Salil Mehta <salil.mehta@huawei.com>,
        Russell King <linux@armlinux.org.uk>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        <jianyong.wu@arm.com>, <justin.he@arm.com>
Subject: Re: [RFC PATCH v2 22/35] ACPI: Check _STA present bit before making
 CPUs not present
Message-ID: <20230914153110.00003e38@Huawei.com>
In-Reply-To: <20230913163823.7880-23-james.morse@arm.com>
References: <20230913163823.7880-1-james.morse@arm.com>
        <20230913163823.7880-23-james.morse@arm.com>
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On Wed, 13 Sep 2023 16:38:10 +0000
James Morse <james.morse@arm.com> wrote:

> When called acpi_processor_post_eject() unconditionally make a CPU
> not-present and unregisters it.
> 
> To add support for AML events where the CPU has become disabled, but
> remains present, the _STA method should be checked before calling
> acpi_processor_remove().
> 
> Rename acpi_processor_post_eject() acpi_processor_remove_possible(), and
> check the _STA before calling.
> 
> Adding the function prototype for arch_unregister_cpu() allows the
> preprocessor guards to be removed.
> 
> After this change CPUs will remain registered and visible to
> user-space as offline if buggy firmware triggers an eject-request,
> but doesn't clear the corresponding _STA bits after _EJ0 has been
> called.
Will be fun to see how many such buggy firmwares are out there.

> 
> Signed-off-by: James Morse <james.morse@arm.com>

Comment inline but not directly related to this patch so with or
without that change
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

> ---
>  drivers/acpi/acpi_processor.c | 31 +++++++++++++++++++++++++------
>  include/linux/cpu.h           |  1 +
>  2 files changed, 26 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> index 00dcc23d49a8..2cafea1edc24 100644
> --- a/drivers/acpi/acpi_processor.c
> +++ b/drivers/acpi/acpi_processor.c
> @@ -457,13 +457,12 @@ static int acpi_processor_add(struct acpi_device *device,
>  	return result;
>  }
>  
> -#ifdef CONFIG_ACPI_HOTPLUG_PRESENT_CPU
>  /* Removal */
> -static void acpi_processor_post_eject(struct acpi_device *device)
> +static void acpi_processor_make_not_present(struct acpi_device *device)
>  {
>  	struct acpi_processor *pr;
>  
> -	if (!device || !acpi_driver_data(device))
> +	if (!IS_ENABLED(CONFIG_ACPI_HOTPLUG_PRESENT_CPU))

Would it be possible to do all the ifdef to IS_ENABLED changes in a separate
patch?  I haven't figure out if any of them have dependencies on the other
changes, but they do create a bunch of noise I'd rather not see in the more
complex corners of this.

>  		return;
>  
>  	pr = acpi_driver_data(device);
> @@ -501,7 +500,29 @@ static void acpi_processor_post_eject(struct acpi_device *device)
>  	free_cpumask_var(pr->throttling.shared_cpu_map);
>  	kfree(pr);
>  }
> -#endif /* CONFIG_ACPI_HOTPLUG_PRESENT_CPU */
> +
> +static void acpi_processor_post_eject(struct acpi_device *device)
> +{
> +	struct acpi_processor *pr;
> +	unsigned long long sta;
> +	acpi_status status;
> +
> +	if (!device)
> +		return;
> +
> +	pr = acpi_driver_data(device);
> +	if (!pr || pr->id >= nr_cpu_ids || invalid_phys_cpuid(pr->phys_id))
> +		return;
> +
> +	status = acpi_evaluate_integer(pr->handle, "_STA", NULL, &sta);
> +	if (ACPI_FAILURE(status))
> +		return;
> +
> +	if (cpu_present(pr->id) && !(sta & ACPI_STA_DEVICE_PRESENT)) {
> +		acpi_processor_make_not_present(device);
> +		return;
> +	}
> +}
>  
>  #ifdef CONFIG_ARCH_MIGHT_HAVE_ACPI_PDC
>  bool __init processor_physically_present(acpi_handle handle)
> @@ -626,9 +647,7 @@ static const struct acpi_device_id processor_device_ids[] = {
>  static struct acpi_scan_handler processor_handler = {
>  	.ids = processor_device_ids,
>  	.attach = acpi_processor_add,
> -#ifdef CONFIG_ACPI_HOTPLUG_PRESENT_CPU
>  	.post_eject = acpi_processor_post_eject,
> -#endif
>  	.hotplug = {
>  		.enabled = true,
>  	},
> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
> index a71691d7c2ca..e117c06e0c6b 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -81,6 +81,7 @@ struct device *cpu_device_create(struct device *parent, void *drvdata,
>  				 const struct attribute_group **groups,
>  				 const char *fmt, ...);
>  extern int arch_register_cpu(int cpu);
> +extern void arch_unregister_cpu(int cpu);
>  #ifdef CONFIG_HOTPLUG_CPU
>  extern void unregister_cpu(struct cpu *cpu);
>  extern ssize_t arch_cpu_probe(const char *, size_t);