accel/kvm: refactor dirty ring setup

Refactor setting up of dirty ring code in kvm_init() so that is can be
reused in the future patchsets.

Signed-off-by: Ani Sinha <anisinha@redhat.com>
Link: https://lore.kernel.org/r/20240912061838.4501-1-anisinha@redhat.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

accel/kvm/kvm-all.c

@@ -2435,6 +2435,55 @@ static int find_kvm_machine_type(MachineState *ms)
     return type;
 }
 
+static int kvm_setup_dirty_ring(KVMState *s)
+{
+    uint64_t dirty_log_manual_caps;
+    int ret;
+
+    /*
+     * Enable KVM dirty ring if supported, otherwise fall back to
+     * dirty logging mode
+     */
+    ret = kvm_dirty_ring_init(s);
+    if (ret < 0) {
+        return ret;
+    }
+
+    /*
+     * KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 is not needed when dirty ring is
+     * enabled.  More importantly, KVM_DIRTY_LOG_INITIALLY_SET will assume no
+     * page is wr-protected initially, which is against how kvm dirty ring is
+     * usage - kvm dirty ring requires all pages are wr-protected at the very
+     * beginning.  Enabling this feature for dirty ring causes data corruption.
+     *
+     * TODO: Without KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 and kvm clear dirty log,
+     * we may expect a higher stall time when starting the migration.  In the
+     * future we can enable KVM_CLEAR_DIRTY_LOG to work with dirty ring too:
+     * instead of clearing dirty bit, it can be a way to explicitly wr-protect
+     * guest pages.
+     */
+    if (!s->kvm_dirty_ring_size) {
+        dirty_log_manual_caps =
+            kvm_check_extension(s, KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2);
+        dirty_log_manual_caps &= (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE |
+                                  KVM_DIRTY_LOG_INITIALLY_SET);
+        s->manual_dirty_log_protect = dirty_log_manual_caps;
+        if (dirty_log_manual_caps) {
+            ret = kvm_vm_enable_cap(s, KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2, 0,
+                                    dirty_log_manual_caps);
+            if (ret) {
+                warn_report("Trying to enable capability %"PRIu64" of "
+                            "KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 but failed. "
+                            "Falling back to the legacy mode. ",
+                            dirty_log_manual_caps);
+                s->manual_dirty_log_protect = 0;
+            }
+        }
+    }
+
+    return 0;
+}
+
 static int kvm_init(MachineState *ms)
 {
     MachineClass *mc = MACHINE_GET_CLASS(ms);
@@ -2454,7 +2503,6 @@ static int kvm_init(MachineState *ms)
     const KVMCapabilityInfo *missing_cap;
     int ret;
     int type;
-    uint64_t dirty_log_manual_caps;
 
     qemu_mutex_init(&kml_slots_lock);
 
@@ -2566,47 +2614,11 @@ static int kvm_init(MachineState *ms)
     s->coalesced_pio = s->coalesced_mmio &&
                        kvm_check_extension(s, KVM_CAP_COALESCED_PIO);
 
-    /*
+    ret = kvm_setup_dirty_ring(s);
-     * Enable KVM dirty ring if supported, otherwise fall back to
-     * dirty logging mode
-     */
-    ret = kvm_dirty_ring_init(s);
     if (ret < 0) {
         goto err;
     }
 
-    /*
-     * KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 is not needed when dirty ring is
-     * enabled.  More importantly, KVM_DIRTY_LOG_INITIALLY_SET will assume no
-     * page is wr-protected initially, which is against how kvm dirty ring is
-     * usage - kvm dirty ring requires all pages are wr-protected at the very
-     * beginning.  Enabling this feature for dirty ring causes data corruption.
-     *
-     * TODO: Without KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 and kvm clear dirty log,
-     * we may expect a higher stall time when starting the migration.  In the
-     * future we can enable KVM_CLEAR_DIRTY_LOG to work with dirty ring too:
-     * instead of clearing dirty bit, it can be a way to explicitly wr-protect
-     * guest pages.
-     */
-    if (!s->kvm_dirty_ring_size) {
-        dirty_log_manual_caps =
-            kvm_check_extension(s, KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2);
-        dirty_log_manual_caps &= (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE |
-                                  KVM_DIRTY_LOG_INITIALLY_SET);
-        s->manual_dirty_log_protect = dirty_log_manual_caps;
-        if (dirty_log_manual_caps) {
-            ret = kvm_vm_enable_cap(s, KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2, 0,
-                                    dirty_log_manual_caps);
-            if (ret) {
-                warn_report("Trying to enable capability %"PRIu64" of "
-                            "KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 but failed. "
-                            "Falling back to the legacy mode. ",
-                            dirty_log_manual_caps);
-                s->manual_dirty_log_protect = 0;
-            }
-        }
-    }
-
 #ifdef KVM_CAP_VCPU_EVENTS
     s->vcpu_events = kvm_check_extension(s, KVM_CAP_VCPU_EVENTS);
 #endif