target/i386: kvm: initialize feature MSRs very early

Some read-only MSRs affect the behavior of ioctls such as
KVM_SET_NESTED_STATE.  We can initialize them once and for all
right after the CPU is realized, since they will never be modified
by the guest.
Reported-by: NQingua Cheng <qcheng@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Message-Id: <1579544504-3616-2-git-send-email-pbonzini@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

target/i386/kvm.c

@@ -67,6 +67,8 @@
  * 255 kvm_msr_entry structs */
 #define MSR_BUF_SIZE 4096
 
+static void kvm_init_msrs(X86CPU *cpu);
+
 const KVMCapabilityInfo kvm_arch_required_capabilities[] = {
     KVM_CAP_INFO(SET_TSS_ADDR),
     KVM_CAP_INFO(EXT_CPUID),
@@ -1842,6 +1844,8 @@ int kvm_arch_init_vcpu(CPUState *cs)
         has_msr_tsc_aux = false;
     }
 
+    kvm_init_msrs(cpu);
+
     r = hyperv_init_vcpu(cpu);
     if (r) {
         goto fail;
@@ -2660,11 +2664,53 @@ static void kvm_msr_entry_add_vmx(X86CPU *cpu, FeatureWordArray f)
                       VMCS12_MAX_FIELD_INDEX << 1);
 }
 
+static int kvm_buf_set_msrs(X86CPU *cpu)
+{
+    int ret = kvm_vcpu_ioctl(CPU(cpu), KVM_SET_MSRS, cpu->kvm_msr_buf);
+    if (ret < 0) {
+        return ret;
+    }
+
+    if (ret < cpu->kvm_msr_buf->nmsrs) {
+        struct kvm_msr_entry *e = &cpu->kvm_msr_buf->entries[ret];
+        error_report("error: failed to set MSR 0x%" PRIx32 " to 0x%" PRIx64,
+                     (uint32_t)e->index, (uint64_t)e->data);
+    }
+
+    assert(ret == cpu->kvm_msr_buf->nmsrs);
+    return 0;
+}
+
+static void kvm_init_msrs(X86CPU *cpu)
+{
+    CPUX86State *env = &cpu->env;
+
+    kvm_msr_buf_reset(cpu);
+    if (has_msr_arch_capabs) {
+        kvm_msr_entry_add(cpu, MSR_IA32_ARCH_CAPABILITIES,
+                          env->features[FEAT_ARCH_CAPABILITIES]);
+    }
+
+    if (has_msr_core_capabs) {
+        kvm_msr_entry_add(cpu, MSR_IA32_CORE_CAPABILITY,
+                          env->features[FEAT_CORE_CAPABILITY]);
+    }
+
+    /*
+     * Older kernels do not include VMX MSRs in KVM_GET_MSR_INDEX_LIST, but
+     * all kernels with MSR features should have them.
+     */
+    if (kvm_feature_msrs && cpu_has_vmx(env)) {
+        kvm_msr_entry_add_vmx(cpu, env->features);
+    }
+
+    assert(kvm_buf_set_msrs(cpu) == 0);
+}
+
 static int kvm_put_msrs(X86CPU *cpu, int level)
 {
     CPUX86State *env = &cpu->env;
     int i;
-    int ret;
 
     kvm_msr_buf_reset(cpu);
 
@@ -2722,17 +2768,6 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
     }
 #endif
 
-    /* If host supports feature MSR, write down. */
-    if (has_msr_arch_capabs) {
-        kvm_msr_entry_add(cpu, MSR_IA32_ARCH_CAPABILITIES,
-                          env->features[FEAT_ARCH_CAPABILITIES]);
-    }
-
-    if (has_msr_core_capabs) {
-        kvm_msr_entry_add(cpu, MSR_IA32_CORE_CAPABILITY,
-                          env->features[FEAT_CORE_CAPABILITY]);
-    }
-
     /*
      * The following MSRs have side effects on the guest or are too heavy
      * for normal writeback. Limit them to reset or full state updates.
@@ -2910,14 +2945,6 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
 
         /* Note: MSR_IA32_FEATURE_CONTROL is written separately, see
          *       kvm_put_msr_feature_control. */
-
-        /*
-         * Older kernels do not include VMX MSRs in KVM_GET_MSR_INDEX_LIST, but
-         * all kernels with MSR features should have them.
-         */
-        if (kvm_feature_msrs && cpu_has_vmx(env)) {
-            kvm_msr_entry_add_vmx(cpu, env->features);
-        }
     }
 
     if (env->mcg_cap) {
@@ -2933,19 +2960,7 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
         }
     }
 
-    ret = kvm_vcpu_ioctl(CPU(cpu), KVM_SET_MSRS, cpu->kvm_msr_buf);
-    if (ret < 0) {
-        return ret;
-    }
-
-    if (ret < cpu->kvm_msr_buf->nmsrs) {
-        struct kvm_msr_entry *e = &cpu->kvm_msr_buf->entries[ret];
-        error_report("error: failed to set MSR 0x%" PRIx32 " to 0x%" PRIx64,
-                     (uint32_t)e->index, (uint64_t)e->data);
-    }
-
-    assert(ret == cpu->kvm_msr_buf->nmsrs);
-    return 0;
+    return kvm_buf_set_msrs(cpu);
 }
 
 

target/i386/kvm_i386.h

@@ -46,4 +46,5 @@ bool kvm_enable_x2apic(void);
 bool kvm_has_x2apic_api(void);
 
 bool kvm_hv_vpindex_settable(void);
+
 #endif