linux-kernel - Re: [PATCH 3/3] x86/acpi, x86/boot: Add multiprocessor wake-up support

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Date:   Fri, 23 Apr 2021 01:04:44 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Rafael J Wysocki <rjw@...ysocki.net>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Len Brown <lenb@...nel.org>, Robert Moore <robert.moore@...el.com>,
        Erik Kaneda <erik.kaneda@...el.com>,
        linux-acpi@...r.kernel.org, devel@...ica.org,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 3/3] x86/acpi, x86/boot: Add multiprocessor wake-up support

Kuppuswamy!

On Thu, Apr 22 2021 at 12:24, Kuppuswamy Sathyanarayanan wrote:
> +static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
> +{
> +	acpi_mp_wake_mailbox_init();
> +
> +	if (!acpi_mp_wake_mailbox)
> +		return -EINVAL;
> +
> +	WRITE_ONCE(acpi_mp_wake_mailbox->apic_id, apicid);
> +	WRITE_ONCE(acpi_mp_wake_mailbox->wakeup_vector, start_ip);
> +	WRITE_ONCE(acpi_mp_wake_mailbox->command, ACPI_MP_WAKE_COMMAND_WAKEUP);

What's the point of using WRITE_ONCE() here? Where is the required
READ_ONCE() counterpart and the required documentation in form of a
comment?

> +static int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
> +				      const unsigned long end)
> +{
...
> +	acpi_wake_cpu_handler_update(acpi_wakeup_cpu);
...

> +++ b/arch/x86/kernel/apic/probe_32.c
> @@ -207,3 +207,11 @@ int __init default_acpi_madt_oem_check(char *oem_id, char *oem_table_id)
>  	}
>  	return 0;
>  }
> +
> +void __init acpi_wake_cpu_handler_update(wakeup_cpu_handler handler)
> +{
> +	struct apic **drv;
> +
> +	for (drv = __apicdrivers; drv < __apicdrivers_end; drv++)
> +		(*drv)->wakeup_secondary_cpu = handler;
> +}
> diff --git a/arch/x86/kernel/apic/probe_64.c b/arch/x86/kernel/apic/probe_64.c
> index c46720f185c0..986dbb68d3c4 100644
> --- a/arch/x86/kernel/apic/probe_64.c
> +++ b/arch/x86/kernel/apic/probe_64.c
> @@ -50,3 +50,11 @@ int __init default_acpi_madt_oem_check(char *oem_id, char *oem_table_id)
>  	}
>  	return 0;
>  }
> +
> +void __init acpi_wake_cpu_handler_update(wakeup_cpu_handler handler)
> +{
> +	struct apic **drv;
> +
> +	for (drv = __apicdrivers; drv < __apicdrivers_end; drv++)
> +		(*drv)->wakeup_secondary_cpu = handler;
> +}

What's the reason for having two verbatim copies of the same function
which has no dependency on CONFIG_*_32/64 at all?

Thanks,

        tglx