libxc: make xc_domain_maximum_gpfn() endianness-agnostic

libxc generally uses uint32_t to represent domain IDs. This is fine as
long as addresses of such variables aren't taken, to then pass into
hypercalls: To the hypervisor, a domain ID is a 16-bit value. Introduce
a wrapper struct to deal with the issue. (On architectures with
arguments passed in registers, an intermediate variable would have been
created by the compiler already anyway, just one of the wrong type.)

The public interface change is both source and binary compatible for
the architectures we currently support.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Ian Jackson <iwj@xenproject.org>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

tools/libs/ctrl/xc_domain.c

@@ -856,7 +856,8 @@ int xc_domain_get_tsc_info(xc_interface *xch,
 
 int xc_domain_maximum_gpfn(xc_interface *xch, uint32_t domid, xen_pfn_t *gpfns)
 {
-    long rc = do_memory_op(xch, XENMEM_maximum_gpfn, &domid, sizeof(domid));
+    struct xen_memory_domain dom = { .domid = domid };
+    long rc = do_memory_op(xch, XENMEM_maximum_gpfn, &dom, sizeof(dom));
 
     if ( rc >= 0 )
     {

xen/common/memory.c

@@ -1351,7 +1351,6 @@ long do_memory_op(unsigned long cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
     long rc;
     struct xen_memory_reservation reservation;
     struct memop_args args;
-    domid_t domid;
     unsigned long start_extent = cmd >> MEMOP_EXTENT_SHIFT;
     int op = cmd & MEMOP_CMD_MASK;
 
@@ -1452,13 +1451,16 @@ long do_memory_op(unsigned long cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
     case XENMEM_current_reservation:
     case XENMEM_maximum_reservation:
     case XENMEM_maximum_gpfn:
+    {
+        struct xen_memory_domain domain;
+
         if ( unlikely(start_extent) )
             return -EINVAL;
 
-        if ( copy_from_guest(&domid, arg, 1) )
+        if ( copy_from_guest(&domain, arg, 1) )
             return -EFAULT;
 
-        d = rcu_lock_domain_by_any_id(domid);
+        d = rcu_lock_domain_by_any_id(domain.domid);
         if ( d == NULL )
             return -ESRCH;
 
@@ -1486,6 +1488,7 @@ long do_memory_op(unsigned long cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
         rcu_unlock_domain(d);
 
         break;
+    }
 
     case XENMEM_add_to_physmap:
     {

xen/include/public/memory.h

@@ -148,16 +148,23 @@ DEFINE_XEN_GUEST_HANDLE(xen_memory_exchange_t);
  */
 #define XENMEM_maximum_ram_page     2
 
+struct xen_memory_domain {
+    /* [IN] Domain information is being queried for. */
+    domid_t domid;
+};
+
 /*
  * Returns the current or maximum memory reservation, in pages, of the
  * specified domain (may be DOMID_SELF). Returns -ve errcode on failure.
- * arg == addr of domid_t.
+ * arg == addr of struct xen_memory_domain.
  */
 #define XENMEM_current_reservation  3
 #define XENMEM_maximum_reservation  4
 
 /*
- * Returns the maximum GPFN in use by the guest, or -ve errcode on failure.
+ * Returns the maximum GFN in use by the specified domain (may be DOMID_SELF).
+ * Returns -ve errcode on failure.
+ * arg == addr of struct xen_memory_domain.
  */
 #define XENMEM_maximum_gpfn         14