libxc: Fix xc_mem_event.c compilation for ARM

The commit 6ae2df9 "mem_access: Add helper API to setup ring and enable
mem_access¨ break libxc compilation for ARM.

This is because xc_map_foreign_map and xc_domain_decrease_reservation_exact
is taking an xen_pfn_t in parameters. On ARM, xen_pfn_t is always an uin64_t.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Cc: Aravindh Puthiyaparambil <aravindp@cisco.com>
Cc: Jan Beulich <jbeulich@suse.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/libxc/xc_mem_event.c

@@ -60,7 +60,8 @@ void *xc_mem_event_enable(xc_interface *xch, domid_t domain_id, int param,
                           uint32_t *port)
 {
     void *ring_page = NULL;
-    unsigned long ring_pfn, mmap_pfn;
+    unsigned long pfn;
+    xen_pfn_t ring_pfn, mmap_pfn;
     unsigned int op, mode;
     int rc1, rc2, saved_errno;
 
@@ -79,14 +80,15 @@ void *xc_mem_event_enable(xc_interface *xch, domid_t domain_id, int param,
     }
 
     /* Get the pfn of the ring page */
-    rc1 = xc_get_hvm_param(xch, domain_id, param, &ring_pfn);
+    rc1 = xc_get_hvm_param(xch, domain_id, param, &pfn);
     if ( rc1 != 0 )
     {
         PERROR("Failed to get pfn of ring page\n");
         goto out;
     }
 
-    mmap_pfn = ring_pfn;
+    ring_pfn = pfn;
+    mmap_pfn = pfn;
     ring_page = xc_map_foreign_batch(xch, domain_id, PROT_READ | PROT_WRITE,
                                      &mmap_pfn, 1);
     if ( mmap_pfn & XEN_DOMCTL_PFINFO_XTAB )