linux-kernel - Re: [RFC PATCH v2 16/35] ACPI: processor: Register CPUs that are online, but not described in the DSDT

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Message-ID: <82ce8528-49ae-3937-4020-0666fe416c0a@redhat.com>
Date:   Mon, 18 Sep 2023 15:12:06 +1000
From:   Gavin Shan <gshan@...hat.com>
To:     James Morse <james.morse@....com>, 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
Cc:     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 16/35] ACPI: processor: Register CPUs that are
 online, but not described in the DSDT



On 9/14/23 02:38, James Morse wrote:
> ACPI has two descriptions of CPUs, one in the MADT/APIC table, the other
> in the DSDT. Both are required. (ACPI 6.5's 8.4 "Declaring Processors"
> says "Each processor in the system must be declared in the ACPI
> namespace"). Having two descriptions allows firmware authors to get
> this wrong.
> 
> If CPUs are described in the MADT/APIC, they will be brought online
> early during boot. Once the register_cpu() calls are moved to ACPI,
> they will be based on the DSDT description of the CPUs. When CPUs are
> missing from the DSDT description, they will end up online, but not
> registered.
> 
> Add a helper that runs after acpi_init() has completed to register
> CPUs that are online, but weren't found in the DSDT. Any CPU that
> is registered by this code triggers a firmware-bug warning and kernel
> taint.
> 
> Qemu TCG only describes the first CPU in the DSDT, unless cpu-hotplug
> is configured.
> 
> Signed-off-by: James Morse <james.morse@....com>
> ---
>   drivers/acpi/acpi_processor.c | 19 +++++++++++++++++++
>   1 file changed, 19 insertions(+)
> 

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

> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> index b4bde78121bb..a01e315aa16a 100644
> --- a/drivers/acpi/acpi_processor.c
> +++ b/drivers/acpi/acpi_processor.c
> @@ -790,6 +790,25 @@ void __init acpi_processor_init(void)
>   	acpi_pcc_cpufreq_init();
>   }
>   
> +static int __init acpi_processor_register_missing_cpus(void)
> +{
> +	int cpu;
> +
> +	if (acpi_disabled)
> +		return 0;
> +
> +	for_each_online_cpu(cpu) {
> +		if (!get_cpu_device(cpu)) {
> +			pr_err_once(FW_BUG "CPU %u has no ACPI namespace description!\n", cpu);
> +			add_taint(TAINT_FIRMWARE_WORKAROUND, LOCKDEP_STILL_OK);
> +			arch_register_cpu(cpu);
> +		}
> +	}
> +
> +	return 0;
> +}
> +subsys_initcall_sync(acpi_processor_register_missing_cpus);
> +
>   #ifdef CONFIG_ACPI_PROCESSOR_CSTATE
>   /**
>    * acpi_processor_claim_cst_control - Request _CST control from the platform.