i386/kvm: correct the meaning of '0xffffffff' value for hv-spinlocks

Hyper-V TLFS prior to version 6.0 had a mistake in it: special value
'0xffffffff' for CPUID 0x40000004.EBX was called 'never to retry', this
looked weird (like why it's not '0' which supposedly have the same effect?)
but nobody raised the question. In TLFS version 6.0 the mistake was
corrected to 'never notify' which sounds logical. Fix QEMU accordingly.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20200515114847.74523-1-vkuznets@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

docs/hyperv.txt

@@ -49,7 +49,7 @@ more efficiently. In particular, this enlightenment allows paravirtualized
 ======================
 Enables paravirtualized spinlocks. The parameter indicates how many times
 spinlock acquisition should be attempted before indicating the situation to the
-hypervisor. A special value 0xffffffff indicates "never to retry".
+hypervisor. A special value 0xffffffff indicates "never notify".
 
 3.4. hv-vpindex
 ================

target/i386/cpu.c

@@ -7263,7 +7263,7 @@ static Property x86_cpu_properties[] = {
     DEFINE_PROP_BOOL("pmu", X86CPU, enable_pmu, false),
 
     DEFINE_PROP_UINT32("hv-spinlocks", X86CPU, hyperv_spinlock_attempts,
-                       HYPERV_SPINLOCK_NEVER_RETRY),
+                       HYPERV_SPINLOCK_NEVER_NOTIFY),
     DEFINE_PROP_BIT64("hv-relaxed", X86CPU, hyperv_features,
                       HYPERV_FEAT_RELAXED, 0),
     DEFINE_PROP_BIT64("hv-vapic", X86CPU, hyperv_features,

target/i386/cpu.h

@@ -991,8 +991,8 @@ typedef uint64_t FeatureWordArray[FEATURE_WORDS];
 #define HYPERV_FEAT_IPI                 13
 #define HYPERV_FEAT_STIMER_DIRECT       14
 
-#ifndef HYPERV_SPINLOCK_NEVER_RETRY
-#define HYPERV_SPINLOCK_NEVER_RETRY             0xFFFFFFFF
+#ifndef HYPERV_SPINLOCK_NEVER_NOTIFY
+#define HYPERV_SPINLOCK_NEVER_NOTIFY             0xFFFFFFFF
 #endif
 
 #define EXCP00_DIVZ	0

target/i386/kvm.c

@@ -730,7 +730,7 @@ static bool hyperv_enabled(X86CPU *cpu)
 {
     CPUState *cs = CPU(cpu);
     return kvm_check_extension(cs->kvm_state, KVM_CAP_HYPERV) > 0 &&
-        ((cpu->hyperv_spinlock_attempts != HYPERV_SPINLOCK_NEVER_RETRY) ||
+        ((cpu->hyperv_spinlock_attempts != HYPERV_SPINLOCK_NEVER_NOTIFY) ||
          cpu->hyperv_features || cpu->hyperv_passthrough);
 }
 
@@ -1236,7 +1236,7 @@ static int hyperv_handle_properties(CPUState *cs,
             env->features[FEAT_HV_RECOMM_EAX] = c->eax;
 
             /* hv-spinlocks may have been overriden */
-            if (cpu->hyperv_spinlock_attempts != HYPERV_SPINLOCK_NEVER_RETRY) {
+            if (cpu->hyperv_spinlock_attempts != HYPERV_SPINLOCK_NEVER_NOTIFY) {
                 c->ebx = cpu->hyperv_spinlock_attempts;
             }
         }