[RFC v3 1/3] kvm: Add a notifier for create and destroy VM events

[Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx>]

After registering with this notifier, other drivers that are dependent
on KVM can get notified whenever a VM is created or destroyed. This
also provides a way for sharing the KVM instance pointer with other
drivers.

Signed-off-by: Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx>
---
 include/linux/kvm_host.h |  5 +++++
 virt/kvm/kvm_main.c      | 20 ++++++++++++++++++--
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index f3b1013fb22c..fc1a688301a0 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -88,6 +88,9 @@
 #define KVM_PFN_ERR_HWPOISON	(KVM_PFN_ERR_MASK + 1)
 #define KVM_PFN_ERR_RO_FAULT	(KVM_PFN_ERR_MASK + 2)
 
+#define KVM_EVENT_CREATE_VM 0
+#define KVM_EVENT_DESTROY_VM 1
+
 /*
  * error pfns indicate that the gfn is in slot but faild to
  * translate it to pfn on host.
@@ -1494,5 +1497,7 @@ static inline void kvm_handle_signal_exit(struct kvm_vcpu *vcpu)
 
 /* Max number of entries allowed for each kvm dirty ring */
 #define  KVM_DIRTY_RING_MAX_ENTRIES  65536
+int kvm_vm_register_notifier(struct notifier_block *nb);
+int kvm_vm_unregister_notifier(struct notifier_block *nb);
 
 #endif
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5f260488e999..8a0e8bb02a5f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -101,6 +101,8 @@ DEFINE_MUTEX(kvm_lock);
 static DEFINE_RAW_SPINLOCK(kvm_count_lock);
 LIST_HEAD(vm_list);
 
+static struct blocking_notifier_head kvm_vm_notifier;
+
 static cpumask_var_t cpus_hardware_enabled;
 static int kvm_usage_count;
 static atomic_t hardware_enable_failed;
@@ -148,12 +150,20 @@ static void kvm_io_bus_destroy(struct kvm_io_bus *bus);
 __visible bool kvm_rebooting;
 EXPORT_SYMBOL_GPL(kvm_rebooting);
 
-#define KVM_EVENT_CREATE_VM 0
-#define KVM_EVENT_DESTROY_VM 1
 static void kvm_uevent_notify_change(unsigned int type, struct kvm *kvm);
 static unsigned long long kvm_createvm_count;
 static unsigned long long kvm_active_vms;
 
+inline int kvm_vm_register_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&kvm_vm_notifier, nb);
+}
+
+inline int kvm_vm_unregister_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&kvm_vm_notifier, nb);
+}
+
 __weak void kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm,
 						   unsigned long start, unsigned long end)
 {
@@ -808,6 +818,8 @@ static struct kvm *kvm_create_vm(unsigned long type)
 
 	preempt_notifier_inc();
 
+	blocking_notifier_call_chain(&kvm_vm_notifier,
+				     KVM_EVENT_CREATE_VM, kvm);
 	return kvm;
 
 out_err:
@@ -886,6 +898,8 @@ static void kvm_destroy_vm(struct kvm *kvm)
 	preempt_notifier_dec();
 	hardware_disable_all();
 	mmdrop(mm);
+	blocking_notifier_call_chain(&kvm_vm_notifier,
+				     KVM_EVENT_DESTROY_VM, kvm);
 }
 
 void kvm_get_kvm(struct kvm *kvm)
@@ -4968,6 +4982,8 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
 	r = kvm_vfio_ops_init();
 	WARN_ON(r);
 
+	BLOCKING_INIT_NOTIFIER_HEAD(&kvm_vm_notifier);
+
 	return 0;
 
 out_unreg:
-- 
2.26.2

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