i386: reorder call to cpu_exec_realizefn

i386 realizefn code is sensitive to ordering, and recent commits
aimed at refactoring it, splitting accelerator-specific code,
broke assumptions which need to be fixed.

We need to:

* process hyper-v enlightements first, as they assume features
  not to be expanded

* only then, expand features

* after expanding features, attempt to check them and modify them in the
  accel-specific realizefn code called by cpu_exec_realizefn().

* after the framework has been called via cpu_exec_realizefn,
  the code can check for what has or hasn't been set by accel-specific
  code, or extend its results, ie:

  - check and evenually set code_urev default
  - modify cpu->mwait after potentially being set from host CPUID.
  - finally check for phys_bits assuming all user and accel-specific
    adjustments have already been taken into account.

Fixes: f5cc5a5c ("i386: split cpu accelerators from cpu.c"...)
Fixes: 30565f10 ("cpu: call AccelCPUClass::cpu_realizefn in"...)
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Claudio Fontana <cfontana@suse.de>
Message-Id: <20210603123001.17843-2-cfontana@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

2 files changed, 61 insertions, 30 deletions

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index e0ba36cc23..9c47daa409 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -6089,39 +6089,17 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
     Error *local_err = NULL;
     static bool ht_warned;
 
-    /* Process Hyper-V enlightenments */
-    x86_cpu_hyperv_realize(cpu);
-
-    cpu_exec_realizefn(cs, &local_err);
-    if (local_err != NULL) {
-        error_propagate(errp, local_err);
-        return;
-    }
-
-    if (xcc->host_cpuid_required && !accel_uses_host_cpuid()) {
-        g_autofree char *name = x86_cpu_class_get_model_name(xcc);
-        error_setg(&local_err, "CPU model '%s' requires KVM or HVF", name);
-        goto out;
-    }
-
-    if (cpu->ucode_rev == 0) {
-        /* The default is the same as KVM's.  */
-        if (IS_AMD_CPU(env)) {
-            cpu->ucode_rev = 0x01000065;
-        } else {
-            cpu->ucode_rev = 0x100000000ULL;
-        }
-    }
-
-    /* mwait extended info: needed for Core compatibility */
-    /* We always wake on interrupt even if host does not have the capability */
-    cpu->mwait.ecx |= CPUID_MWAIT_EMX | CPUID_MWAIT_IBE;
-
     if (cpu->apic_id == UNASSIGNED_APIC_ID) {
         error_setg(errp, "apic-id property was not initialized properly");
         return;
     }
 
+    /*
+     * Process Hyper-V enlightenments.
+     * Note: this currently has to happen before the expansion of CPU features.
+     */
+    x86_cpu_hyperv_realize(cpu);
+
     x86_cpu_expand_features(cpu, &local_err);
     if (local_err) {
         goto out;
@@ -6146,11 +6124,56 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
            & CPUID_EXT2_AMD_ALIASES);
     }
 
+    /*
+     * note: the call to the framework needs to happen after feature expansion,
+     * but before the checks/modifications to ucode_rev, mwait, phys_bits.
+     * These may be set by the accel-specific code,
+     * and the results are subsequently checked / assumed in this function.
+     */
+    cpu_exec_realizefn(cs, &local_err);
+    if (local_err != NULL) {
+        error_propagate(errp, local_err);
+        return;
+    }
+
+    if (xcc->host_cpuid_required && !accel_uses_host_cpuid()) {
+        g_autofree char *name = x86_cpu_class_get_model_name(xcc);
+        error_setg(&local_err, "CPU model '%s' requires KVM or HVF", name);
+        goto out;
+    }
+
+    if (cpu->ucode_rev == 0) {
+        /*
+         * The default is the same as KVM's. Note that this check
+         * needs to happen after the evenual setting of ucode_rev in
+         * accel-specific code in cpu_exec_realizefn.
+         */
+        if (IS_AMD_CPU(env)) {
+            cpu->ucode_rev = 0x01000065;
+        } else {
+            cpu->ucode_rev = 0x100000000ULL;
+        }
+    }
+
+    /*
+     * mwait extended info: needed for Core compatibility
+     * We always wake on interrupt even if host does not have the capability.
+     *
+     * requires the accel-specific code in cpu_exec_realizefn to
+     * have already acquired the CPUID data into cpu->mwait.
+     */
+    cpu->mwait.ecx |= CPUID_MWAIT_EMX | CPUID_MWAIT_IBE;
+
     /* For 64bit systems think about the number of physical bits to present.
      * ideally this should be the same as the host; anything other than matching
      * the host can cause incorrect guest behaviour.
      * QEMU used to pick the magic value of 40 bits that corresponds to
      * consumer AMD devices but nothing else.
+     *
+     * Note that this code assumes features expansion has already been done
+     * (as it checks for CPUID_EXT2_LM), and also assumes that potential
+     * phys_bits adjustments to match the host have been already done in
+     * accel-specific code in cpu_exec_realizefn.
      */
     if (env->features[FEAT_8000_0001_EDX] & CPUID_EXT2_LM) {
         if (cpu->phys_bits &&
diff --git a/target/i386/kvm/kvm-cpu.c b/target/i386/kvm/kvm-cpu.c
index 5235bce8dc..00369c2000 100644
--- a/target/i386/kvm/kvm-cpu.c
+++ b/target/i386/kvm/kvm-cpu.c
@@ -26,10 +26,18 @@ static bool kvm_cpu_realizefn(CPUState *cs, Error **errp)
     /*
      * The realize order is important, since x86_cpu_realize() checks if
      * nothing else has been set by the user (or by accelerators) in
-     * cpu->ucode_rev and cpu->phys_bits.
+     * cpu->ucode_rev and cpu->phys_bits, and updates the CPUID results in
+     * mwait.ecx.
+     * This accel realization code also assumes cpu features are already expanded.
      *
      * realize order:
-     * kvm_cpu -> host_cpu -> x86_cpu
+     *
+     * x86_cpu_realize():
+     *  -> x86_cpu_expand_features()
+     *  -> cpu_exec_realizefn():
+     *            -> accel_cpu_realizefn()
+     *               kvm_cpu_realizefn() -> host_cpu_realizefn()
+     *  -> check/update ucode_rev, phys_bits, mwait
      */
     if (cpu->max_features) {
         if (enable_cpu_pm && kvm_has_waitpkg()) {