Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.35 as permitted sender) client-ip=23.128.96.35;
Date:   Thu, 14 Sep 2023 14:56:07 +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>,
        <linux-kernel@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <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 16/35] ACPI: processor: Register CPUs that are
 online, but not described in the DSDT
Message-ID: <20230914145607.00006f9b@Huawei.com>
In-Reply-To: <20230913163823.7880-17-james.morse@arm.com>
References: <20230913163823.7880-1-james.morse@arm.com>
        <20230913163823.7880-17-james.morse@arm.com>
Organization: Huawei Technologies Research and Development (UK) Ltd.
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
Content-Transfer-Encoding: 7bit
Precedence: bulk

On Wed, 13 Sep 2023 16:38:04 +0000
James Morse <james.morse@arm.com> 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.

We should fix that as who likes warnings and taint :)
I dread to think how common this will turn out to be.

> 
> Signed-off-by: James Morse <james.morse@arm.com>
LGTM
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

> ---
>  drivers/acpi/acpi_processor.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> 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.