target/arm: Query host CPU features on-demand at instance init

Currently we query the host CPU features in the class init function
for the TYPE_ARM_HOST_CPU class, so that we can later copy them
from the class object into the instance object in the object
instance init function. This is awkward for implementing "-cpu max",
which should work like "-cpu host" for KVM but like "cpu with all
implemented features" for TCG.

Move the place where we store the information about the host CPU from
a class object to static variables in kvm.c, and then in the instance
init function call a new kvm_arm_set_cpu_features_from_host()
function which will query the host kernel if necessary and then
fill in the CPU instance fields.

This allows us to drop the special class struct and class init
function for TYPE_ARM_HOST_CPU entirely.

We can't delay the probe until realize, because the ARM
instance_post_init hook needs to look at the feature bits we
set, so we need to do it in the initfn. This is safe because
the probing doesn't affect the actual VM state (it creates a
separate scratch VM to do its testing), but the probe might fail.
Because we can't report errors in retrieving the host features
in the initfn, we check this belatedly in the realize function
(the intervening code will be able to cope with the relevant
fields in the CPU structure being zero).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20180308130626.12393-2-peter.maydell@linaro.org

1 files changed, 19 insertions, 17 deletions

diff --git a/target/arm/kvm.c b/target/arm/kvm.c
index 1219d0062b..1c0e57690a 100644
--- a/target/arm/kvm.c
+++ b/target/arm/kvm.c
@@ -33,6 +33,8 @@ const KVMCapabilityInfo kvm_arch_required_capabilities[] = {
 
 static bool cap_has_mp_state;
 
+static ARMHostCPUFeatures arm_host_cpu_features;
+
 int kvm_arm_vcpu_init(CPUState *cs)
 {
     ARMCPU *cpu = ARM_CPU(cs);
@@ -129,30 +131,32 @@ void kvm_arm_destroy_scratch_host_vcpu(int *fdarray)
     }
 }
 
-static void kvm_arm_host_cpu_class_init(ObjectClass *oc, void *data)
+void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu)
 {
-    ARMHostCPUClass *ahcc = ARM_HOST_CPU_CLASS(oc);
+    CPUARMState *env = &cpu->env;
 
-    /* All we really need to set up for the 'host' CPU
-     * is the feature bits -- we rely on the fact that the
-     * various ID register values in ARMCPU are only used for
-     * TCG CPUs.
-     */
-    if (!kvm_arm_get_host_cpu_features(ahcc)) {
-        fprintf(stderr, "Failed to retrieve host CPU features!\n");
-        abort();
+    if (!arm_host_cpu_features.dtb_compatible) {
+        if (!kvm_enabled() ||
+            !kvm_arm_get_host_cpu_features(&arm_host_cpu_features)) {
+            /* We can't report this error yet, so flag that we need to
+             * in arm_cpu_realizefn().
+             */
+            cpu->kvm_target = QEMU_KVM_ARM_TARGET_NONE;
+            cpu->host_cpu_probe_failed = true;
+            return;
+        }
     }
+
+    cpu->kvm_target = arm_host_cpu_features.target;
+    cpu->dtb_compatible = arm_host_cpu_features.dtb_compatible;
+    env->features = arm_host_cpu_features.features;
 }
 
 static void kvm_arm_host_cpu_initfn(Object *obj)
 {
-    ARMHostCPUClass *ahcc = ARM_HOST_CPU_GET_CLASS(obj);
     ARMCPU *cpu = ARM_CPU(obj);
-    CPUARMState *env = &cpu->env;
 
-    cpu->kvm_target = ahcc->target;
-    cpu->dtb_compatible = ahcc->dtb_compatible;
-    env->features = ahcc->features;
+    kvm_arm_set_cpu_features_from_host(cpu);
 }
 
 static const TypeInfo host_arm_cpu_type_info = {
@@ -163,8 +167,6 @@ static const TypeInfo host_arm_cpu_type_info = {
     .parent = TYPE_ARM_CPU,
 #endif
     .instance_init = kvm_arm_host_cpu_initfn,
-    .class_init = kvm_arm_host_cpu_class_init,
-    .class_size = sizeof(ARMHostCPUClass),
 };
 
 int kvm_arch_init(MachineState *ms, KVMState *s)