IOMMU: add missing HVM check

Fix an unguarded d->arch.hvm access in assign_device().

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/drivers/passthrough/pci.c

@@ -1488,7 +1488,8 @@ static int assign_device(struct domain *d, u16 seg, u8 bus, u8 devfn, u32 flag)
 
     /* Prevent device assign if mem paging or mem sharing have been 
      * enabled for this domain */
-    if ( unlikely(d->arch.hvm.mem_sharing_enabled ||
+    if ( unlikely((is_hvm_domain(d) &&
+                   d->arch.hvm.mem_sharing_enabled) ||
                   vm_event_check_ring(d->vm_event_paging) ||
                   p2m_get_hostp2m(d)->global_logdirty) )
         return -EXDEV;