[tip:x86/apic] x86/apic: Introduce apic_extnmi command line parameter

tip-bot for Hidehiro Kawai
2015-12-19T10:15:28Z

Commit-ID: b7c4948e9881fb38b048269f376fb4bf194ce24a
Gitweb: http://git.kernel.org/tip/b7c4948e9881fb38b048269f376fb4bf194ce24a
Author: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
AuthorDate: Mon, 14 Dec 2015 11:19:12 +0100
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Sat, 19 Dec 2015 11:07:01 +0100

x86/apic: Introduce apic_extnmi command line parameter

This patch introduces a command line parameter apic_extnmi:

apic_extnmi=( bsp|all|none )

The default value is "bsp" and this is the current behavior: only the
Boot-Strapping Processor receives an 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 in NMI context
or the external NMI is swallowed by other NMI handlers on the BSP.

If you specify "none", no CPUs receive external NMIs. This is useful for
the dump capture kernel so that it cannot be shot down by accidentally
pressing the external NMI button (on platforms which have it) while
saving a crash dump.

Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Bandan Das <bsd@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: kexec@lists.infradead.org
Cc: linux-doc@vger.kernel.org
Cc: "Maciej W. Rozycki" <macro@linux-mips.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: x86-ml <x86@kernel.org>
Link: http://lkml.kernel.org/r/20151210014632.25437.43778.stgit@softrs
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
Documentation/kernel-parameters.txt | 9 +++++++++
arch/x86/include/asm/apic.h | 5 +++++
arch/x86/kernel/apic/apic.c | 34 ++++++++++++++++++++++++++++++++--
3 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 742f69d..74acea5 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 only to CPU 0
+ 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 8d7df74..8a5cdda 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 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);
}

@@ -1378,9 +1386,11 @@ void setup_local_APIC(void)
apic_write(APIC_LVT0, value);

/*
- * only the BP should see the LINT1 NMI signal, obviously.
+ * Only the BSP sees the LINT1 NMI signal by default. This can be
+ * modified by apic_extnmi= boot option.
*/
- 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;
@@ -2557,3 +2567,23 @@ 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 (!strncmp("all", arg, 3))
+ apic_extnmi = APIC_EXTNMI_ALL;
+ else if (!strncmp("none", arg, 4))
+ apic_extnmi = APIC_EXTNMI_NONE;
+ else if (!strncmp("bsp", arg, 3))
+ apic_extnmi = APIC_EXTNMI_BSP;
+ else {
+ pr_warn("Unknown external NMI delivery mode `%s' ignored\n", arg);
+ return -EINVAL;
+ }
+
+ return 0;
+}
+early_param("apic_extnmi", apic_set_extnmi);