[PATCH 1/2] x86/boot: Fix setup_apic_nmi_watchdog() to fail more cleanly

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Right now, if the user requests the watchdog on the command line,
setup_apic_nmi_watchdog() will blindly assume that setting up the watchdog
worked.  Reuse nmi_perfctr_msr to identify when the watchdog has been set up.

Rearrange setup_p6_watchdog() to not set nmi_perfctr_msr until the sanity
checks are performed.  Turn setup_p4_watchdog() into a void function, matching
the others.

If the watchdog isn't set up, inform the user and override to NMI_NONE, which
will prevent check_nmi_watchdog() from claiming that all CPUs are stuck.

e.g.:

  (XEN) alt table ffff82d040697c38 -> ffff82d0406a97f0
  (XEN) Failed to configure NMI watchdog
  (XEN) Brought up 512 CPUs
  (XEN) Scheduling granularity: cpu, 1 CPU per sched-resource

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>

This is all horrible code.
---
 xen/arch/x86/nmi.c | 25 ++++++++++++-------------
 1 file changed, 12 insertions(+), 13 deletions(-)

diff --git a/xen/arch/x86/nmi.c b/xen/arch/x86/nmi.c
index 8994c50cb5e4..33f77a92047f 100644
--- a/xen/arch/x86/nmi.c
+++ b/xen/arch/x86/nmi.c
@@ -319,8 +319,6 @@ static void setup_p6_watchdog(unsigned counter)
 {
     unsigned int evntsel;
 
-    nmi_perfctr_msr = MSR_P6_PERFCTR(0);
-
     if ( !nmi_p6_event_width && current_cpu_data.cpuid_level >= 0xa )
         nmi_p6_event_width = MASK_EXTR(cpuid_eax(0xa), P6_EVENT_WIDTH_MASK);
     if ( !nmi_p6_event_width )
@@ -330,6 +328,8 @@ static void setup_p6_watchdog(unsigned counter)
          nmi_p6_event_width > BITS_PER_LONG )
         return;
 
+    nmi_perfctr_msr = MSR_P6_PERFCTR(0);
+
     clear_msr_range(MSR_P6_EVNTSEL(0), 2);
     clear_msr_range(MSR_P6_PERFCTR(0), 2);
 
@@ -345,13 +345,13 @@ static void setup_p6_watchdog(unsigned counter)
     wrmsr(MSR_P6_EVNTSEL(0), evntsel, 0);
 }
 
-static int setup_p4_watchdog(void)
+static void setup_p4_watchdog(void)
 {
     uint64_t misc_enable;
 
     rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
     if (!(misc_enable & MSR_IA32_MISC_ENABLE_PERF_AVAIL))
-        return 0;
+        return;
 
     nmi_perfctr_msr = MSR_P4_IQ_PERFCTR0;
     nmi_p4_cccr_val = P4_NMI_IQ_CCCR0;
@@ -374,13 +374,12 @@ static int setup_p4_watchdog(void)
     clear_msr_range(0x3E0, 2);
     clear_msr_range(MSR_P4_BPU_CCCR0, 18);
     clear_msr_range(MSR_P4_BPU_PERFCTR0, 18);
-        
+
     wrmsrl(MSR_P4_CRU_ESCR0, P4_NMI_CRU_ESCR0);
     wrmsrl(MSR_P4_IQ_CCCR0, P4_NMI_IQ_CCCR0 & ~P4_CCCR_ENABLE);
     write_watchdog_counter("P4_IQ_COUNTER0");
     apic_write(APIC_LVTPC, APIC_DM_NMI);
     wrmsrl(MSR_P4_IQ_CCCR0, nmi_p4_cccr_val);
-    return 1;
 }
 
 void setup_apic_nmi_watchdog(void)
@@ -395,8 +394,6 @@ void setup_apic_nmi_watchdog(void)
         case 0xf ... 0x19:
             setup_k7_watchdog();
             break;
-        default:
-            return;
         }
         break;
     case X86_VENDOR_INTEL:
@@ -407,14 +404,16 @@ void setup_apic_nmi_watchdog(void)
                               : CORE_EVENT_CPU_CLOCKS_NOT_HALTED);
             break;
         case 15:
-            if (!setup_p4_watchdog())
-                return;
+            setup_p4_watchdog();
             break;
-        default:
-            return;
         }
         break;
-    default:
+    }
+
+    if ( nmi_perfctr_msr == 0 )
+    {
+        printk(XENLOG_WARNING "Failed to configure NMI watchdog\n");
+        nmi_watchdog = NMI_NONE;
         return;
     }
 
-- 
2.30.2