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>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 742f69d18fc8989ae28d9c0662d6bf334109dddd..74acea53e9e372d91230d24ce537ea447fa09618 100644 (file)
--- 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 7f62ad47d7e4342f490d8daf138040f5002fc8e9..c80f6b6f3da222dc86dc00747429b618589502eb 100644 (file)
--- 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 8d7df7478d84a093fbba232b18aa75b4e3fb03b9..8a5cddac7d444084c223e95948944b5099d15003 100644 (file)
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -81,6 +81,12 @@ 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
  */
@@ -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);