streamline guest copy operations

- use the variants not validating the VA range when writing back
  structures/fields to the same space that they were previously read
  from
- when only a single field of a structure actually changed, copy back
  just that field where possible
- consolidate copying back results in a few places

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/xen/common/memory.c b/xen/common/memory.c
index b7fdd77c0f..c8541c4f9e 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -359,7 +359,7 @@ static long memory_exchange(XEN_GUEST_HANDLE_PARAM(xen_memory_exchange_t) arg)
         {
             exch.nr_exchanged = i << in_chunk_order;
             rcu_unlock_domain(d);
-            if ( copy_field_to_guest(arg, &exch, nr_exchanged) )
+            if ( __copy_field_to_guest(arg, &exch, nr_exchanged) )
                 return -EFAULT;
             return hypercall_create_continuation(
                 __HYPERVISOR_memory_op, "lh", XENMEM_exchange, arg);
@@ -500,7 +500,7 @@ static long memory_exchange(XEN_GUEST_HANDLE_PARAM(xen_memory_exchange_t) arg)
     }
 
     exch.nr_exchanged = exch.in.nr_extents;
-    if ( copy_field_to_guest(arg, &exch, nr_exchanged) )
+    if ( __copy_field_to_guest(arg, &exch, nr_exchanged) )
         rc = -EFAULT;
     rcu_unlock_domain(d);
     return rc;
@@ -527,7 +527,7 @@ static long memory_exchange(XEN_GUEST_HANDLE_PARAM(xen_memory_exchange_t) arg)
     exch.nr_exchanged = i << in_chunk_order;
 
  fail_early:
-    if ( copy_field_to_guest(arg, &exch, nr_exchanged) )
+    if ( __copy_field_to_guest(arg, &exch, nr_exchanged) )
         rc = -EFAULT;
     return rc;
 }