Re: [V5 PATCH 4/4] x86/apic: Introduce apic_extnmi boot option

Borislav Petkov
2015-11-25T11:49:54Z

On Fri, Nov 20, 2015 at 06:36:50PM +0900, Hidehiro Kawai wrote:
> This patch introduces new boot option, apic_extnmi:
>
> apic_extnmi={ bsp | all | none}
>
> The default value is "bsp" and this is the current behavior; only
> BSP receives external NMI. "all" allows external NMIs to be
> broadcast to all CPUs. This would raise the success rate of panic
> on NMI when BSP hangs up in NMI context or the external NMI is
> swallowed by other NMI handlers on BSP. If you specified "none",
> any CPUs don't receive external NMIs. This is useful for dump
> capture kernel so that it wouldn't be shot down while saving a
> crash dump.
>
> V5:
> - Rename the option from "noextnmi" to "apic_extnmi"
> - Add apic_extnmi=all feature
> - Fix the wrong documentation about "noextnmi" (apic_extnmi=none)
>
> Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Jonathan Corbet <corbet@lwn.net>
> ---
> Documentation/kernel-parameters.txt | 9 +++++++++
> arch/x86/include/asm/apic.h | 5 +++++
> arch/x86/kernel/apic/apic.c | 31 ++++++++++++++++++++++++++++++-
> 3 files changed, 44 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index f8aae63..ceed3bc 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -472,6 +472,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> Change the amount of debugging information output
> when initialising the APIC and IO-APIC components.
>
> + apic_extnmi= [APIC,X86] External NMI delivery setting
> + Format: { bsp (default) | all | none }
> + bsp: External NMI is delivered to only CPU 0

only to

> + all: External NMIs are broadcast to all CPUs as a
> + backup of CPU 0
> + none: External NMI is masked for all CPUs. This is
> + useful so that a dump capture kernel won't be
> + shot down by NMI
> +
> autoconf= [IPV6]
> See Documentation/networking/ipv6.txt.
>
> diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
> index 7f62ad4..c80f6b6 100644
> --- a/arch/x86/include/asm/apic.h
> +++ b/arch/x86/include/asm/apic.h
> @@ -23,6 +23,11 @@
> #define APIC_VERBOSE 1
> #define APIC_DEBUG 2
>
> +/* Macros for apic_extnmi which controls external NMI masking */
> +#define APIC_EXTNMI_BSP 0 /* Default */
> +#define APIC_EXTNMI_ALL 1
> +#define APIC_EXTNMI_NONE 2
> +
> /*
> * Define the default level of output to be very little
> * This can be turned up by using apic=verbose for more
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index 2f69e3b..a2a8074 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -82,6 +82,12 @@ physid_mask_t phys_cpu_present_map;
> static unsigned int disabled_cpu_apicid __read_mostly = BAD_APICID;
>
> /*
> + * This variable controls which CPUs receive external NMIs. By default,
> + * external NMIs are delivered to only BSP.

only to the BSP.

> + */
> +static int apic_extnmi = APIC_EXTNMI_BSP;
> +
> +/*
> * Map cpu index to physical APIC ID
> */
> DEFINE_EARLY_PER_CPU_READ_MOSTLY(u16, x86_cpu_to_apicid, BAD_APICID);
> @@ -1161,6 +1167,8 @@ void __init init_bsp_APIC(void)
> value = APIC_DM_NMI;
> if (!lapic_is_integrated()) /* 82489DX */
> value |= APIC_LVT_LEVEL_TRIGGER;
> + if (apic_extnmi == APIC_EXTNMI_NONE)
> + value |= APIC_LVT_MASKED;
> apic_write(APIC_LVT1, value);
> }
>
> @@ -1380,7 +1388,8 @@ void setup_local_APIC(void)
> /*
> * only the BP should see the LINT1 NMI signal, obviously.
> */

That comment needs adjusting.

> - if (!cpu)
> + if ((!cpu && apic_extnmi != APIC_EXTNMI_NONE) ||
> + apic_extnmi == APIC_EXTNMI_ALL)
> value = APIC_DM_NMI;
> else
> value = APIC_DM_NMI | APIC_LVT_MASKED;
> @@ -2548,3 +2557,23 @@ static int __init apic_set_disabled_cpu_apicid(char *arg)
> return 0;
> }
> early_param("disable_cpu_apicid", apic_set_disabled_cpu_apicid);
> +
> +static int __init apic_set_extnmi(char *arg)
> +{
> + if (!arg)
> + return -EINVAL;
> +
> + if (strcmp("all", arg) == 0)

if (!strncmp("all", arg, 3))

ditto for the rest

> + apic_extnmi = APIC_EXTNMI_ALL;
> + else if (strcmp("none", arg) == 0)
> + apic_extnmi = APIC_EXTNMI_NONE;
> + else if (strcmp("bsp", arg) == 0)
> + apic_extnmi = APIC_EXTNMI_BSP;
> + else {
> + pr_warn("Unknown external NMI delivery mode `%s' is ignored\n",

s/is //

Also, if there's no other delivery mode which makes sense, you can do:

pr_warn("Unknown external NMI delivery mode `%s', defaulting to 'bsp'\n", arg);
apic_extnmi = APIC_EXTNMI_BSP;

Btw, you can let the pr_warn line be longer than 80 cols.

And if you don't default, you need

return -EINVAL;

here.

--
Regards/Gruss,
Boris.

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