[PATCH 4.4 04/36] KVM: s390: Disable dirty log retrieval for UCONTROL guests

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Janosch Frank <frankja@linux.vnet.ibm.com>

commit e1e8a9624f7ba8ead4f056ff558ed070e86fa747 upstream.

User controlled KVM guests do not support the dirty log, as they have
no single gmap that we can check for changes.

As they have no single gmap, kvm->arch.gmap is NULL and all further
referencing to it for dirty checking will result in a NULL
dereference.

Let's return -EINVAL if a caller tries to sync dirty logs for a
UCONTROL guest.

Fixes: 15f36eb ("KVM: s390: Add proper dirty bitmap support to S390 kvm.")
Signed-off-by: Janosch Frank <frankja@linux.vnet.ibm.com>
Reported-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/s390/kvm/kvm-s390.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -295,6 +295,9 @@ int kvm_vm_ioctl_get_dirty_log(struct kv
 	struct kvm_memory_slot *memslot;
 	int is_dirty = 0;
 
+	if (kvm_is_ucontrol(kvm))
+		return -EINVAL;
+
 	mutex_lock(&kvm->slots_lock);
 
 	r = -EINVAL;