[xen master] x86/nmi: Don't configure EvtSel repeatedly

[patchbot@xxxxxxx]

commit 669f8c502aeaa538f8407013ba04461e71361ed4
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Aug 4 22:45:53 2026 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Aug 18 12:51:59 2026 +0100

    x86/nmi: Don't configure EvtSel repeatedly
    
    In both setup_{k7,p6}_watchdog(), EvtSel0 is first zeroed, then written with
    everything but the enable bit, then written with the enable bit.
    
    setup_p4_watchdog() is slightly more complicated, owing to what
    appears to be a bug introduced by commit 2a2bd8de16b6 ("Clean up NMI
    watchdog handler."), which causes a second bit to be temporarily
    different too.
    
    The middle of the three writes is useless in all cases.  Drop it.
    
    While doing this, rename the 'counter' parameter for
    setup_p6_watchdog().  It is the event which is passed in; the counter
    is always counter 0.
    
    No functional change.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/nmi.c | 29 +++++++----------------------
 1 file changed, 7 insertions(+), 22 deletions(-)

diff --git a/xen/arch/x86/nmi.c b/xen/arch/x86/nmi.c
index f7603ce369..b3d18270b1 100644
--- a/xen/arch/x86/nmi.c
+++ b/xen/arch/x86/nmi.c
@@ -246,29 +246,20 @@ static inline void write_watchdog_counter(const char 
*descr)
 
 static void setup_k7_watchdog(void)
 {
-    unsigned int evntsel;
-
     nmi_perfctr_msr = MSR_K7_PERFCTR0;
 
     clear_msr_range(MSR_K7_EVNTSEL0, 4);
     clear_msr_range(MSR_K7_PERFCTR0, 4);
 
-    evntsel = K7_EVNTSEL_INT
-        | K7_EVNTSEL_OS
-        | K7_EVNTSEL_USR
-        | K7_EVENT_CYCLES_PROCESSOR_IS_RUNNING;
-
-    wrmsrns(MSR_K7_EVNTSEL0, evntsel);
     write_watchdog_counter("K7_PERFCTR0");
     apic_write(APIC_LVTPC, APIC_DM_NMI);
-    evntsel |= K7_EVNTSEL_ENABLE;
-    wrmsrns(MSR_K7_EVNTSEL0, evntsel);
+    wrmsrns(MSR_K7_EVNTSEL0,
+            K7_EVNTSEL_ENABLE | K7_EVNTSEL_INT | K7_EVNTSEL_OS |
+            K7_EVNTSEL_USR | K7_EVENT_CYCLES_PROCESSOR_IS_RUNNING);
 }
 
-static void setup_p6_watchdog(unsigned counter)
+static void setup_p6_watchdog(unsigned int event)
 {
-    unsigned int evntsel;
-
     if ( !nmi_p6_event_width && boot_cpu_data.cpuid_level >= 0xa )
         nmi_p6_event_width = MASK_EXTR(cpuid_eax(0xa), P6_EVENT_WIDTH_MASK);
     if ( !nmi_p6_event_width )
@@ -283,16 +274,11 @@ static void setup_p6_watchdog(unsigned counter)
     clear_msr_range(MSR_P6_EVNTSEL(0), 2);
     clear_msr_range(MSR_P6_PERFCTR(0), 2);
 
-    evntsel = P6_EVNTSEL_INT
-        | P6_EVNTSEL_OS
-        | P6_EVNTSEL_USR
-        | counter;
-
-    wrmsrns(MSR_P6_EVNTSEL(0), evntsel);
     write_watchdog_counter("P6_PERFCTR0");
     apic_write(APIC_LVTPC, APIC_DM_NMI);
-    evntsel |= P6_EVNTSEL0_ENABLE;
-    wrmsrns(MSR_P6_EVNTSEL(0), evntsel);
+    wrmsrns(MSR_P6_EVNTSEL(0),
+            P6_EVNTSEL0_ENABLE | P6_EVNTSEL_INT | P6_EVNTSEL_OS |
+            P6_EVNTSEL_USR | event);
 }
 
 static void setup_p4_watchdog(uint64_t misc_enable)
@@ -316,7 +302,6 @@ static void setup_p4_watchdog(uint64_t misc_enable)
     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);
--
generated by git-patchbot for /home/xen/git/xen.git#master