KVM: Allow to have arch-specific per-vm debugfs files

Allow archs to create arch-specific nodes under kvm->debugfs_dentry directory
besides the stats fields.  The new interface kvm_arch_create_vm_debugfs() is
defined but not yet used.  It's called after kvm->debugfs_dentry is created, so
it can be referenced directly in kvm_arch_create_vm_debugfs().  Arch should
define their own versions when they want to create extra debugfs nodes.
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20210730220455.26054-2-peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/linux/kvm_host.h

@@ -1073,6 +1073,7 @@ bool kvm_arch_dy_runnable(struct kvm_vcpu *vcpu);
 bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu);
 int kvm_arch_post_init_vm(struct kvm *kvm);
 void kvm_arch_pre_destroy_vm(struct kvm *kvm);
+int kvm_arch_create_vm_debugfs(struct kvm *kvm);
 
 #ifndef __KVM_HAVE_ARCH_VM_ALLOC
 /*

virt/kvm/kvm_main.c

@@ -919,7 +919,7 @@ static int kvm_create_vm_debugfs(struct kvm *kvm, int fd)
 	char dir_name[ITOA_MAX_LEN * 2];
 	struct kvm_stat_data *stat_data;
 	const struct _kvm_stats_desc *pdesc;
-	int i;
+	int i, ret;
 	int kvm_debugfs_num_entries = kvm_vm_stats_header.num_desc +
 				      kvm_vcpu_stats_header.num_desc;
 
@@ -976,6 +976,13 @@ static int kvm_create_vm_debugfs(struct kvm *kvm, int fd)
 				    kvm->debugfs_dentry, stat_data,
 				    &stat_fops_per_vm);
 	}
+
+	ret = kvm_arch_create_vm_debugfs(kvm);
+	if (ret) {
+		kvm_destroy_vm_debugfs(kvm);
+		return i;
+	}
+
 	return 0;
 }
 
@@ -996,6 +1003,17 @@ void __weak kvm_arch_pre_destroy_vm(struct kvm *kvm)
 {
 }
 
+/*
+ * Called after per-vm debugfs created.  When called kvm->debugfs_dentry should
+ * be setup already, so we can create arch-specific debugfs entries under it.
+ * Cleanup should be automatic done in kvm_destroy_vm_debugfs() recursively, so
+ * a per-arch destroy interface is not needed.
+ */
+int __weak kvm_arch_create_vm_debugfs(struct kvm *kvm)
+{
+	return 0;
+}
+
 static struct kvm *kvm_create_vm(unsigned long type)
 {
 	struct kvm *kvm = kvm_arch_alloc_vm();