KVM: Actually create debugfs in kvm_create_vm()

Doing debugfs creation after vm creation leaves things in a
quasi-initialized state for a while. This is further complicated by the
fact that we tear down debugfs from kvm_destroy_vm(). Align debugfs and
stats init/destroy with the vm init/destroy pattern to avoid any
headaches.

Note the fix for a benign mistake in error handling for calls to
kvm_arch_create_vm_debugfs() rolled in. Since all implementations of
the function return 0 unconditionally it isn't actually a bug at
the moment.

Lastly, tear down debugfs/stats data in the kvm_create_vm_debugfs()
error path. Previously it was safe to assume that kvm_destroy_vm() would
take out the garbage, that is no longer the case.

Signed-off-by: Oliver Upton <oupton@google.com>
Message-Id: <20220720092259.3491733-6-oliver.upton@linux.dev>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 8e08f66ddbd418e8fc21e16a14158cc16cf1d4b4..515dfe9d3bcfb09b091f6af83dae7d76210f60dd 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1028,7 +1028,7 @@ static int kvm_create_vm_debugfs(struct kvm *kvm, const char *fdname)
        char dir_name[ITOA_MAX_LEN * 2];
        struct kvm_stat_data *stat_data;
        const struct _kvm_stats_desc *pdesc;
-       int i, ret;
+       int i, ret = -ENOMEM;
        int kvm_debugfs_num_entries = kvm_vm_stats_header.num_desc +
                                      kvm_vcpu_stats_header.num_desc;
 
@@ -1054,13 +1054,13 @@ static int kvm_create_vm_debugfs(struct kvm *kvm, const char *fdname)
                                         sizeof(*kvm->debugfs_stat_data),
                                         GFP_KERNEL_ACCOUNT);
        if (!kvm->debugfs_stat_data)
-               return -ENOMEM;
+               goto out_err;
 
        for (i = 0; i < kvm_vm_stats_header.num_desc; ++i) {
                pdesc = &kvm_vm_stats_desc[i];
                stat_data = kzalloc(sizeof(*stat_data), GFP_KERNEL_ACCOUNT);
                if (!stat_data)
-                       return -ENOMEM;
+                       goto out_err;
 
                stat_data->kvm = kvm;
                stat_data->desc = pdesc;
@@ -1075,7 +1075,7 @@ static int kvm_create_vm_debugfs(struct kvm *kvm, const char *fdname)
                pdesc = &kvm_vcpu_stats_desc[i];
                stat_data = kzalloc(sizeof(*stat_data), GFP_KERNEL_ACCOUNT);
                if (!stat_data)
-                       return -ENOMEM;
+                       goto out_err;
 
                stat_data->kvm = kvm;
                stat_data->desc = pdesc;
@@ -1087,12 +1087,13 @@ static int kvm_create_vm_debugfs(struct kvm *kvm, const char *fdname)
        }
 
        ret = kvm_arch_create_vm_debugfs(kvm);
-       if (ret) {
-               kvm_destroy_vm_debugfs(kvm);
-               return i;
-       }
+       if (ret)
+               goto out_err;
 
        return 0;
+out_err:
+       kvm_destroy_vm_debugfs(kvm);
+       return ret;
 }
 
 /*
@@ -1123,7 +1124,7 @@ int __weak kvm_arch_create_vm_debugfs(struct kvm *kvm)
        return 0;
 }
 
-static struct kvm *kvm_create_vm(unsigned long type)
+static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
 {
        struct kvm *kvm = kvm_arch_alloc_vm();
        struct kvm_memslots *slots;
@@ -1212,7 +1213,7 @@ static struct kvm *kvm_create_vm(unsigned long type)
 
        r = kvm_arch_post_init_vm(kvm);
        if (r)
-               goto out_err;
+               goto out_err_mmu_notifier;
 
        mutex_lock(&kvm_lock);
        list_add(&kvm->vm_list, &vm_list);
@@ -1228,12 +1229,18 @@ static struct kvm *kvm_create_vm(unsigned long type)
         */
        if (!try_module_get(kvm_chardev_ops.owner)) {
                r = -ENODEV;
-               goto out_err;
+               goto out_err_mmu_notifier;
        }
 
+       r = kvm_create_vm_debugfs(kvm, fdname);
+       if (r)
+               goto out_err;
+
        return kvm;
 
 out_err:
+       module_put(kvm_chardev_ops.owner);
+out_err_mmu_notifier:
 #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
        if (kvm->mmu_notifier.ops)
                mmu_notifier_unregister(&kvm->mmu_notifier, current->mm);
@@ -4900,7 +4907,7 @@ static int kvm_dev_ioctl_create_vm(unsigned long type)
 
        snprintf(fdname, sizeof(fdname), "%d", fd);
 
-       kvm = kvm_create_vm(type);
+       kvm = kvm_create_vm(type, fdname);
        if (IS_ERR(kvm)) {
                r = PTR_ERR(kvm);
                goto put_fd;
@@ -4923,11 +4930,6 @@ static int kvm_dev_ioctl_create_vm(unsigned long type)
         * cases it will be called by the final fput(file) and will take
         * care of doing kvm_put_kvm(kvm).
         */
-       if (kvm_create_vm_debugfs(kvm, fdname) < 0) {
-               fput(file);
-               r = -ENOMEM;
-               goto put_fd;
-       }
        kvm_uevent_notify_change(KVM_EVENT_CREATE_VM, kvm);
 
        fd_install(fd, file);