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

河合英宏 / KAWAI，HIDEHIRO
2015-11-25T15:30:07Z

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> 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

Thanks for tha correction.

>
> > + 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.

...and again.

>
> > + */
> > +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.

OK, I'll do that.

>
> > - 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

I'll fix them.

> > + 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 //

I'll fix it, thanks.

> 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;

I intended to keep the previous or initial value of apic_extnmi
because boot option can be specified multiple times. If a user do
that, making the last valid value effective would be natural manner.
This is unclear part of boot option as Ingo pointed, but...

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

I like 80 cols because I'm working with multiple 80-col terminals. :-)

> And if you don't default, you need
>
> return -EINVAL;
>
> here.

You are right. It seems that I deleted it while modifying
around the code.

Regards,
--
Hidehiro Kawai
Hitachi, Ltd. Research & Development Group

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