Re: [Qemu-devel] [PATCH v2 5/7] make hyperv hypercall and guest os id MSRs migratable.

[Paolo Bonzini <pbonzini@redhat.com>]

Il 23/01/2014 14:40, Vadim Rozenfeld ha scritto:
> +    if (hyperv_enabled(cpu) &&
> +        kvm_check_extension(cs->kvm_state, KVM_CAP_HYPERV) > 0) {
>          c->eax = HYPERV_CPUID_MIN;
> +        has_msr_hv_hypercall = true;

The commit message should mention that this is done because the MS docs 
specify HV_X64_MSR_HYPERCALL as a mandatory interface, thus we cannot 
separate relaxed timing (say)---even though in principle it doesn't 
require the MSR.

We probably should split this part of the patch as follows:

diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index 0a21c30..19b1c94 100644
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -72,6 +72,7 @@ static bool has_msr_misc_enable;
  static bool has_msr_bndcfgs;
  static bool has_msr_kvm_steal_time;
  static int lm_capable_kernel;
+static bool has_msr_hv_hypercall;

  static bool has_msr_architectural_pmu;
  static uint32_t num_architectural_pmu_counters;
@@ -437,8 +438,9 @@ static bool hyperv_hypercall_available(X86CPU *cpu)

  static bool hyperv_enabled(X86CPU *cpu)
  {
-    return hyperv_hypercall_available(cpu) ||
-           cpu->hyperv_relaxed_timing;
+    return kvm_check_extension(cs->kvm_state, KVM_CAP_HYPERV) > 0 &&
+           (hyperv_hypercall_available(cpu) ||
+            cpu->hyperv_relaxed_timing);
  }

  #define KVM_MAX_CPUID_ENTRIES  100
@@ -470,6 +472,7 @@ int kvm_arch_init_vcpu(CPUState *cs)
      } else {
          memcpy(signature, "Microsoft Hv", 12);
          c->eax = HYPERV_CPUID_MIN;
+        has_msr_hv_hypercall = true;
      }
      c->ebx = signature[0];
      c->ecx = signature[1];
@@ -479,7 +482,7 @@ int kvm_arch_init_vcpu(CPUState *cs)
      c->function = KVM_CPUID_FEATURES;
      c->eax = env->features[FEAT_KVM];

-    if (hyperv_enabled(cpu)) {
+    if (has_msr_hv_hypercall) {
          memcpy(signature, "Hv#1\0\0\0\0\0\0\0\0", 12);
          c->eax = signature[0];


Paolo