[PATCH RFC v2 19/19] i386: expand Hyper-V features during CPU feature expansion time

[Vitaly Kuznetsov]

To make Hyper-V features appear in e.g. QMP query-cpu-model-expansion we
need to expand and set the corresponding CPUID leaves early. Modify
x86_cpu_get_supported_feature_word() to call newly intoduced Hyper-V
specific kvm_hv_get_supported_cpuid() instead of
kvm_arch_get_supported_cpuid(). We can't use kvm_arch_get_supported_cpuid()
as Hyper-V specific CPUID leaves intersect with KVM's.

Note, early expansion will only happen when KVM supports system wide
KVM_GET_SUPPORTED_HV_CPUID ioctl (KVM_CAP_SYS_HYPERV_CPUID).

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 target/i386/cpu.c      |  4 ++++
 target/i386/kvm-stub.c |  5 +++++
 target/i386/kvm.c      | 15 ++++++++++++---
 target/i386/kvm_i386.h |  1 +
 4 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index a178db255641..272091eab057 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -6345,6 +6345,10 @@ static void x86_cpu_expand_features(X86CPU *cpu, Error 
**errp)
     if (env->cpuid_xlevel2 == UINT32_MAX) {
         env->cpuid_xlevel2 = env->cpuid_min_xlevel2;
     }
+
+    if (kvm_enabled()) {
+        kvm_hyperv_expand_features(cpu, errp);
+    }
 }
 
 /*
diff --git a/target/i386/kvm-stub.c b/target/i386/kvm-stub.c
index 872ef7df4c88..4abb5afa1168 100644
--- a/target/i386/kvm-stub.c
+++ b/target/i386/kvm-stub.c
@@ -44,3 +44,8 @@ bool kvm_hv_vpindex_settable(void)
 {
     return false;
 }
+
+void kvm_hyperv_expand_features(X86CPU *cpu, Error **errp)
+{
+    return;
+}
diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index 2c62122a1bc8..ba99aecb5a64 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -1230,13 +1230,22 @@ static uint32_t hv_build_cpuid_leaf(CPUState *cs, 
uint32_t func, int reg)
  * of 'hv_passthrough' mode and fills the environment with all supported
  * Hyper-V features.
  */
-static void hyperv_expand_features(CPUState *cs, Error **errp)
+void kvm_hyperv_expand_features(X86CPU *cpu, Error **errp)
 {
-    X86CPU *cpu = X86_CPU(cs);
+    CPUState *cs = CPU(cpu);
 
     if (!hyperv_enabled(cpu))
         return;
 
+    /*
+     * When kvm_hyperv_expand_features is called at CPU feature expansion
+     * time per-CPU kvm_state is not available yet so we can only proceed
+     * when KVM_CAP_SYS_HYPERV_CPUID is supported.
+     */
+    if (!cs->kvm_state &&
+        !kvm_check_extension(kvm_state, KVM_CAP_SYS_HYPERV_CPUID))
+        return;
+
     if (cpu->hyperv_passthrough) {
         cpu->hyperv_vendor_id[0] =
             hv_cpuid_get_host(cs, HV_CPUID_VENDOR_AND_MAX_FUNCTIONS, R_EBX);
@@ -1569,7 +1578,7 @@ int kvm_arch_init_vcpu(CPUState *cs)
     env->apic_bus_freq = KVM_APIC_BUS_FREQUENCY;
 
     /* Paravirtualization CPUIDs */
-    hyperv_expand_features(cs, &local_err);
+    kvm_hyperv_expand_features(cpu, &local_err);
     if (local_err) {
         error_report_err(local_err);
         return -ENOSYS;
diff --git a/target/i386/kvm_i386.h b/target/i386/kvm_i386.h
index 064b8798a26c..126a1bcef2dd 100644
--- a/target/i386/kvm_i386.h
+++ b/target/i386/kvm_i386.h
@@ -47,5 +47,6 @@ bool kvm_has_x2apic_api(void);
 bool kvm_has_waitpkg(void);
 
 bool kvm_hv_vpindex_settable(void);
+void kvm_hyperv_expand_features(X86CPU *cpu, Error **errp);
 
 #endif
-- 
2.25.4