gnttab: bail from GFN-storing loops early in case of error

The contents of the output arrays are undefined anyway when the
operation itself gets marked as failed. There's no value in trying to
continue after a guest memory access failure.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/common/compat/grant_table.c

@@ -179,7 +179,10 @@ int compat_grant_table_op(
                             unsigned int frame = (_s_)->frame_list.p[i]; \
                             if ( __copy_to_compat_offset((_d_)->frame_list, \
                                                          i, &frame, 1) ) \
+                            { \
                                 (_s_)->status = GNTST_bad_virt_addr; \
+                                break; \
+                            } \
                         } \
                     } \
                 } while (0)

xen/common/grant_table.c

@@ -2101,7 +2101,10 @@ gnttab_setup_table(
         BUG_ON(SHARED_M2P(gmfn));
 
         if ( __copy_to_guest_offset(op.frame_list, i, &gmfn, 1) )
+        {
             op.status = GNTST_bad_virt_addr;
+            break;
+        }
     }
 
  unlock:
@@ -3311,7 +3314,10 @@ gnttab_get_status_frames(XEN_GUEST_HANDLE_PARAM(gnttab_get_status_frames_t) uop,
     {
         gmfn = gfn_x(gnttab_status_gfn(d, gt, i));
         if ( __copy_to_guest_offset(op.frame_list, i, &gmfn, 1) )
+        {
             op.status = GNTST_bad_virt_addr;
+            break;
+        }
     }
 
  unlock: