linux-kernel - Re: [Patch v2] lapic need be checked if available when initialize acpi processor id

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Message-ID: <20140430060303.GE4774@dhcp-16-105.nay.redhat.com>
Date:	Wed, 30 Apr 2014 14:03:03 +0800
From:	Baoquan He <bhe@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	rjw@...ysocki.net, lenb@...nel.org, linux-acpi@...r.kernel.org,
	jiang.liu@...ux.intel.com, vgoyal@...hat.com
Subject: Re: [Patch v2] lapic need be checked if available when initialize
 acpi processor id

Hi Rafael,

Thanks for previous review for v1. Later on I thought acpi_lapic is
more suitable for checking whether LAPIC in MADT is available, and it can
hanlde both the UP system running SMP kernel with no LAPIC in MADT and kdump
kernel after multiple CPUs system crashed on non-1st CPU.

I tested the 1st case by addding "disableapic nr_cpus=1" into cmdline
of SMP kenrel, and it works. For 2nd case, it works too, below warning
message is not printed any more. 

acpi LNXCPU:0a: BIOS reported wrong ACPI id 0 for the processor

Do you like this idea?

Thanks
Baoquan

On 04/30/14 at 01:55pm, Baoquan He wrote:
> In acpi_processor_get_info(), acpi processor info is initialized including
> id, namely cpu index. Currently, if on UP system running SMP kerenl with
> no LAPIC in MADT, cpu0_initialized is checked if acpi processor id is
> initialized.
> 
> However this check maybe is not correct for kdump kernel. Most of time
> only 1 CPU is supported because of known problems. So in 1st kernel
> multiple CPUs are present, then crash happened in one specific CPU,
> say 2nd CPU. Then it jump into kdump kernel with "nr_cpus=1" specified
> in cmdline. In this situation, since kdump kernel is warm reset, it will
> reuse the ACPI resource passed from crashed kernel directly, namely 1st
> kernel. It means in MADT all LAPIC is enabled while only 1 CPU is
> present in running system. The kdump kernel usually is the same as the
> crashed 1st kernel. So now in kdump kernel, x86_cpu_to_apicid stored the
> apicid and its related cpu id. If only check cpu0_initialized, it will
> assign 0 to the acpi processor id of 1st CPU, it's not correct.
> 
> So in this patch, check acpi_lapic too. If acpi_lapic is 0, then LAPIC in
> MADT is not available, assigne 0 to the handling acpi processor. If
> acpi_lapic is 1, then LAPIC in MADT is available, let's get apic processor
> id from x86_cpu_to_apicid.
> 
> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
>  drivers/acpi/acpi_processor.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> index c29c2c3..33f934d 100644
> --- a/drivers/acpi/acpi_processor.c
> +++ b/drivers/acpi/acpi_processor.c
> @@ -267,7 +267,7 @@ static int acpi_processor_get_info(struct acpi_device *device)
>  	pr->apic_id = apic_id;
>  
>  	cpu_index = acpi_map_cpuid(pr->apic_id, pr->acpi_id);
> -	if (!cpu0_initialized) {
> +	if (!cpu0_initialized && !acpi_lapic) {
>  		cpu0_initialized = 1;
>  		/* Handle UP system running SMP kernel, with no LAPIC in MADT */
>  		if ((cpu_index == -1) && (num_online_cpus() == 1))
> -- 
> 1.8.5.3
> 
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