x86/boot: Fix setup_apic_nmi_watchdog() to fail more cleanly

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
configured.

Rearrange setup_p6_watchdog() to not set nmi_perfctr_msr until the sanity
checks are complete.  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@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: f658321374
master date: 2024-03-19 18:29:37 +0000

xen/arch/x86/nmi.c

@@ -324,8 +324,6 @@ 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 )
@@ -335,6 +333,8 @@ 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);
 
@@ -350,13 +350,13 @@ 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;
@@ -379,13 +379,12 @@ 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)
@@ -400,8 +399,6 @@ void setup_apic_nmi_watchdog(void)
         case 0xf ... 0x19:
             setup_k7_watchdog();
             break;
-        default:
-            return;
         }
         break;
     case X86_VENDOR_INTEL:
@@ -412,14 +409,16 @@ 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;
     }