[xen stable-4.18] x86/boot: Fix setup_apic_nmi_watchdog() to fail more cleanly

[patchbot@xxxxxxx]

commit cb7b84d3d50d13d9762ce96cd03a06becc0ecf9b
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Wed Mar 27 12:20:58 2024 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Mar 27 12:20:58 2024 +0100

    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@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: f658321374687c7339235e1ac643e0427acff717
    master date: 2024-03-19 18:29:37 +0000
---
 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 dc79c25e3f..ac4e7c9bdf 100644
--- a/xen/arch/x86/nmi.c
+++ b/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;
     }
 
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.18