KVM: Simplify coalesced mmio initialization

- add destructor function
- move related allocation into constructor
- add stubs for !CONFIG_KVM_MMIO
Signed-off-by: Avi Kivity <avi@redhat.com>

virt/kvm/coalesced_mmio.c

@@ -92,11 +92,19 @@ static const struct kvm_io_device_ops coalesced_mmio_ops = {
 int kvm_coalesced_mmio_init(struct kvm *kvm)
 {
 	struct kvm_coalesced_mmio_dev *dev;
+	struct page *page;
 	int ret;
 
+	ret = -ENOMEM;
+	page = alloc_page(GFP_KERNEL | __GFP_ZERO);
+	if (!page)
+		goto out_err;
+	kvm->coalesced_mmio_ring = page_address(page);
+
+	ret = -ENOMEM;
 	dev = kzalloc(sizeof(struct kvm_coalesced_mmio_dev), GFP_KERNEL);
 	if (!dev)
-		return -ENOMEM;
+		goto out_free_page;
 	spin_lock_init(&dev->lock);
 	kvm_iodevice_init(&dev->dev, &coalesced_mmio_ops);
 	dev->kvm = kvm;
@@ -104,11 +112,24 @@ int kvm_coalesced_mmio_init(struct kvm *kvm)
 
 	ret = kvm_io_bus_register_dev(kvm, &kvm->mmio_bus, &dev->dev);
 	if (ret < 0)
-		kfree(dev);
+		goto out_free_dev;
+
+	return ret;
 
+out_free_dev:
+	kfree(dev);
+out_free_page:
+	__free_page(page);
+out_err:
 	return ret;
 }
 
+void kvm_coalesced_mmio_free(struct kvm *kvm)
+{
+	if (kvm->coalesced_mmio_ring)
+		free_page((unsigned long)kvm->coalesced_mmio_ring);
+}
+
 int kvm_vm_ioctl_register_coalesced_mmio(struct kvm *kvm,
 				         struct kvm_coalesced_mmio_zone *zone)
 {

virt/kvm/coalesced_mmio.h

@@ -10,6 +10,8 @@
  *
  */
 
+#ifdef CONFIG_KVM_MMIO
+
 #define KVM_COALESCED_MMIO_ZONE_MAX 100
 
 struct kvm_coalesced_mmio_dev {
@@ -21,9 +23,17 @@ struct kvm_coalesced_mmio_dev {
 };
 
 int kvm_coalesced_mmio_init(struct kvm *kvm);
+void kvm_coalesced_mmio_free(struct kvm *kvm);
 int kvm_vm_ioctl_register_coalesced_mmio(struct kvm *kvm,
                                        struct kvm_coalesced_mmio_zone *zone);
 int kvm_vm_ioctl_unregister_coalesced_mmio(struct kvm *kvm,
                                          struct kvm_coalesced_mmio_zone *zone);
 
+#else
+
+static inline int kvm_coalesced_mmio_init(struct kvm *kvm) { return 0; }
+static inline void kvm_coalesced_mmio_free(struct kvm *kvm) { }
+
+#endif
+
 #endif

virt/kvm/kvm_main.c

@@ -51,9 +51,7 @@
 #include <asm/pgtable.h>
 #include <asm-generic/bitops/le.h>
 
-#ifdef KVM_COALESCED_MMIO_PAGE_OFFSET
 #include "coalesced_mmio.h"
-#endif
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/kvm.h>
@@ -468,10 +466,7 @@ static void kvm_destroy_vm(struct kvm *kvm)
 	kvm_free_irq_routing(kvm);
 	kvm_io_bus_destroy(&kvm->pio_bus);
 	kvm_io_bus_destroy(&kvm->mmio_bus);
-#ifdef KVM_COALESCED_MMIO_PAGE_OFFSET
-	if (kvm->coalesced_mmio_ring != NULL)
-		free_page((unsigned long)kvm->coalesced_mmio_ring);
-#endif
+	kvm_coalesced_mmio_free(kvm);
 #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
 	mmu_notifier_unregister(&kvm->mmu_notifier, kvm->mm);
 #else