[PATCH 8/9] gnttab: bail from GFN-storing loops early in case of error

[Jan Beulich <jbeulich@xxxxxxxx>]

The contents of the output arrays are undefined in both cases 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@xxxxxxxx>
---
There's also a curious difference between the two sub-ops wrt the use of
SHARED_M2P().

--- a/xen/common/compat/grant_table.c
+++ b/xen/common/compat/grant_table.c
@@ -170,17 +170,14 @@ int compat_grant_table_op(unsigned int c
             if ( rc == 0 )
             {
 #define XLAT_gnttab_setup_table_HNDL_frame_list(_d_, _s_) \
-                do \
-                { \
-                    if ( (_s_)->status == GNTST_okay ) \
+                do { \
+                    for ( i = 0; (_s_)->status == GNTST_okay && \
+                                 i < (_s_)->nr_frames; ++i ) \
                     { \
-                        for ( i = 0; i < (_s_)->nr_frames; ++i ) \
-                        { \
-                            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; \
-                        } \
+                        compat_pfn_t frame = (_s_)->frame_list.p[i]; \
+                        if ( __copy_to_compat_offset((_d_)->frame_list, \
+                                                     i, &frame, 1) ) \
+                            (_s_)->status = GNTST_bad_virt_addr; \
                     } \
                 } while (0)
                 XLAT_gnttab_setup_table(&cmp.setup, nat.setup);
--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -2103,7 +2103,10 @@ 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:
@@ -3289,17 +3292,15 @@ gnttab_get_status_frames(XEN_GUEST_HANDL
                  "status frames, but has only %u\n",
                  d->domain_id, op.nr_frames, nr_status_frames(gt));
         op.status = GNTST_general_error;
-        goto unlock;
     }
 
-    for ( i = 0; i < op.nr_frames; i++ )
+    for ( i = 0; op.status == GNTST_okay && i < op.nr_frames; i++ )
     {
         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;
     }
 
- unlock:
     grant_read_unlock(gt);
  out2:
     rcu_unlock_domain(d);