x86 kvm page table walks: switch to explicit __get_user()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/x86/kvm/mmu/paging_tmpl.h

@@ -400,7 +400,7 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
 			goto error;
 
 		ptep_user = (pt_element_t __user *)((void *)host_addr + offset);
-		if (unlikely(__copy_from_user(&pte, ptep_user, sizeof(pte))))
+		if (unlikely(__get_user(pte, ptep_user)))
 			goto error;
 		walker->ptep_user[walker->level - 1] = ptep_user;