x86/shadow: use __put_user() instead of __copy_to_user()

In a subsequent patch I would almost have broken the logic here, if I
hadn't happened to read through the comment at the top of
safe_write_entry(): __copy_from_user() does not provide a guarantee
shadow_write_entries() requires - it's only an optimization that it
makes use of __put_user_size() for certain sizes. Use __put_user()
directly, which does expand to a single (memory accessing) insn.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Tim Deegan <tim@xen.org>

diff --git a/xen/arch/x86/mm/shadow/multi.c b/xen/arch/x86/mm/shadow/multi.c
index d24ccde0353ca8643acc9d2babd42c44b5f59f29..da46eae835cbfaeb82399c28f7d3b48a52816db8 100644 (file)
--- a/xen/arch/x86/mm/shadow/multi.c
+++ b/xen/arch/x86/mm/shadow/multi.c
@@ -776,9 +776,9 @@ shadow_write_entries(void *d, void *s, int entries, mfn_t mfn)
     /* Because we mirror access rights at all levels in the shadow, an
      * l2 (or higher) entry with the RW bit cleared will leave us with
      * no write access through the linear map.
-     * We detect that by writing to the shadow with copy_to_user() and
+     * We detect that by writing to the shadow with __put_user() and
      * using map_domain_page() to get a writeable mapping if we need to. */
-    if ( __copy_to_user(d, d, sizeof (unsigned long)) != 0 )
+    if ( __put_user(*dst, dst) )
     {
         perfc_incr(shadow_linear_map_failed);
         map = map_domain_page(mfn);