[Xen-devel] [PATCH v3] x86/NMI: Allow processing unknown NMIs when watchdog is enabled

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

Change NMI processing so that if watchdog=force is passed on the
command-line and the NMI is not caused by a perf counter overflow (i.e.
likely not a watchdog "tick"), the NMI is handled by the unknown NMI
handler.

This allows injection of NMIs from IPMI controllers that don't set the
IOCK/SERR bits to trigger the unknown NMI handler rather than be
ignored.

Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
CC: Keir Fraser <keir@xxxxxxx>
CC: Jan Beulich <jbeulich@xxxxxxxx>
---

Changes since V2:
Fix processing when watchdog is turned off.

Changes since V1:
Most of the original behavior is now restored. Now, only if
watchdog=force is given on the command-line and the NMI is not a
watchdog tick (i.e. the perf counter has not overflowed) will the
unknown NMI handler be invoked.

 docs/misc/xen-command-line.markdown |  6 ++++--
 xen/arch/x86/nmi.c                  | 39 +++++++++++++++++++++++++++++++++++--
 xen/arch/x86/traps.c                |  7 ++++---
 xen/include/asm-x86/apic.h          |  2 +-
 xen/include/asm-x86/nmi.h           |  3 +++
 5 files changed, 49 insertions(+), 8 deletions(-)

diff --git a/docs/misc/xen-command-line.markdown 
b/docs/misc/xen-command-line.markdown
index a8cab59..1cbcca4 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -1245,12 +1245,14 @@ As the BTS virtualisation is not 100% safe and because 
of the nehalem quirk
 don't use the vpmu flag on production systems with Intel cpus!
 
 ### watchdog
-> `= <boolean>`
+> `= force | <boolean>`
 
 > Default: `false`
 
 Run an NMI watchdog on each processor.  If a processor is stuck for
-longer than the **watchdog\_timeout**, a panic occurs.
+longer than the **watchdog\_timeout**, a panic occurs.  When `force` is
+specified, in addition to running an NMI watchdog on each processor,
+unknown NMIs will still be processed.
 
 ### watchdog\_timeout
 > `= <integer>`
diff --git a/xen/arch/x86/nmi.c b/xen/arch/x86/nmi.c
index c4427a6..873427f 100644
--- a/xen/arch/x86/nmi.c
+++ b/xen/arch/x86/nmi.c
@@ -43,7 +43,18 @@ static DEFINE_PER_CPU(unsigned int, nmi_timer_ticks);
 
 /* opt_watchdog: If true, run a watchdog NMI on each processor. */
 bool_t __initdata opt_watchdog = 0;
-boolean_param("watchdog", opt_watchdog);
+
+/* watchdog_force: If true, process unknown NMIs when running the watchdog. */
+bool_t watchdog_force = 0;
+
+static void __init parse_watchdog(char * s)
+{
+    opt_watchdog = !!parse_bool(s);
+
+    if ( !strcmp(s, "force") )
+        watchdog_force = 1;
+}
+custom_param("watchdog", parse_watchdog);
 
 /* opt_watchdog_timeout: Number of seconds to wait before panic. */
 static unsigned int opt_watchdog_timeout = 5;
@@ -82,6 +93,7 @@ int nmi_active;
 #define K7_EVNTSEL_USR         (1 << 16)
 #define K7_EVENT_CYCLES_PROCESSOR_IS_RUNNING   0x76
 #define K7_NMI_EVENT           K7_EVENT_CYCLES_PROCESSOR_IS_RUNNING
+#define K7_EVENT_WIDTH          32
 
 #define P6_EVNTSEL0_ENABLE     (1 << 22)
 #define P6_EVNTSEL_INT         (1 << 20)
@@ -89,10 +101,12 @@ int nmi_active;
 #define P6_EVNTSEL_USR         (1 << 16)
 #define P6_EVENT_CPU_CLOCKS_NOT_HALTED  0x79
 #define CORE_EVENT_CPU_CLOCKS_NOT_HALTED 0x3c
+#define P6_EVENT_WIDTH          32
 
 #define P4_ESCR_EVENT_SELECT(N)        ((N)<<25)
 #define P4_CCCR_OVF_PMI0       (1<<26)
 #define P4_CCCR_OVF_PMI1       (1<<27)
+#define P4_CCCR_OVF            (1<<31)
 #define P4_CCCR_THRESHOLD(N)   ((N)<<20)
 #define P4_CCCR_COMPLEMENT     (1<<19)
 #define P4_CCCR_COMPARE                (1<<18)
@@ -432,8 +446,10 @@ int __init watchdog_setup(void)
     return 0;
 }
 
-void nmi_watchdog_tick(const struct cpu_user_regs *regs)
+/* Returns false if this was not a watchdog NMI, true otherwise */
+bool_t nmi_watchdog_tick(const struct cpu_user_regs *regs)
 {
+    bool_t watchdog_tick = 1;
     unsigned int sum = this_cpu(nmi_timer_ticks);
 
     if ( (this_cpu(last_irq_sums) == sum) && watchdog_enabled() )
@@ -459,8 +475,15 @@ void nmi_watchdog_tick(const struct cpu_user_regs *regs)
 
     if ( nmi_perfctr_msr )
     {
+        uint64_t msr_content;
+
+        /* Work out if this is a watchdog tick by checking for overflow. */
         if ( nmi_perfctr_msr == MSR_P4_IQ_PERFCTR0 )
         {
+            rdmsrl(MSR_P4_IQ_CCCR0, msr_content);
+            if ( !(msr_content & P4_CCCR_OVF) )
+                watchdog_tick = 0;
+
             /*
              * P4 quirks:
              * - An overflown perfctr will assert its interrupt
@@ -473,14 +496,26 @@ void nmi_watchdog_tick(const struct cpu_user_regs *regs)
         }
         else if ( nmi_perfctr_msr == MSR_P6_PERFCTR0 )
         {
+            rdmsrl(MSR_P6_PERFCTR0, msr_content);
+            if ( msr_content & (1ULL << P6_EVENT_WIDTH) )
+                watchdog_tick = 0;
+
             /*
              * Only P6 based Pentium M need to re-unmask the apic vector but
              * it doesn't hurt other P6 variants.
              */
             apic_write(APIC_LVTPC, APIC_DM_NMI);
         }
+        else if ( nmi_perfctr_msr == MSR_K7_PERFCTR0 )
+        {
+            rdmsrl(MSR_K7_PERFCTR0, msr_content);
+            if ( msr_content & (1ULL << K7_EVENT_WIDTH) )
+                watchdog_tick = 0;
+        }
         write_watchdog_counter(NULL);
     }
+
+    return watchdog_tick;
 }
 
 /*
diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 71be2ae..7f5306f 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -3306,14 +3306,15 @@ void do_nmi(const struct cpu_user_regs *regs)
 {
     unsigned int cpu = smp_processor_id();
     unsigned char reason;
+    bool_t handle_unknown = 0;
 
     ++nmi_count(cpu);
 
     if ( nmi_callback(regs, cpu) )
         return;
 
-    if ( nmi_watchdog )
-        nmi_watchdog_tick(regs);
+    if ( !nmi_watchdog || (!nmi_watchdog_tick(regs) && watchdog_force) )
+        handle_unknown = 1;
 
     /* Only the BSP gets external NMIs from the system. */
     if ( cpu == 0 )
@@ -3323,7 +3324,7 @@ void do_nmi(const struct cpu_user_regs *regs)
             pci_serr_error(regs);
         if ( reason & 0x40 )
             io_check_error(regs);
-        if ( !(reason & 0xc0) && !nmi_watchdog )
+        if ( !(reason & 0xc0) && handle_unknown )
             unknown_nmi_error(regs, reason);
     }
 }
diff --git a/xen/include/asm-x86/apic.h b/xen/include/asm-x86/apic.h
index 5d7623f..6697245 100644
--- a/xen/include/asm-x86/apic.h
+++ b/xen/include/asm-x86/apic.h
@@ -206,7 +206,7 @@ extern void release_lapic_nmi(void);
 extern void self_nmi(void);
 extern void disable_timer_nmi_watchdog(void);
 extern void enable_timer_nmi_watchdog(void);
-extern void nmi_watchdog_tick (const struct cpu_user_regs *regs);
+extern bool_t nmi_watchdog_tick (const struct cpu_user_regs *regs);
 extern int APIC_init_uniprocessor (void);
 extern void disable_APIC_timer(void);
 extern void enable_APIC_timer(void);
diff --git a/xen/include/asm-x86/nmi.h b/xen/include/asm-x86/nmi.h
index 4504fe1..2c92db9 100644
--- a/xen/include/asm-x86/nmi.h
+++ b/xen/include/asm-x86/nmi.h
@@ -8,6 +8,9 @@ struct cpu_user_regs;
 
 /* Watchdog boolean from the command line */
 extern bool_t opt_watchdog;
+
+/* Watchdog force parameter from the command line */
+extern bool_t watchdog_force;
  
 typedef int (*nmi_callback_t)(const struct cpu_user_regs *regs, int cpu);
  
-- 
1.9.3


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