xen: mapcache: Add function to check if the mapcache is enabled

Add function to check if the mapcache is enabled.
No functional change.

Signed-off-by: Edgar E. Iglesias <edgar.iglesias@amd.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

hw/xen/xen-mapcache.c

@@ -80,6 +80,12 @@ static MapCache *mapcache_grants_ro;
 static MapCache *mapcache_grants_rw;
 static xengnttab_handle *xen_region_gnttabdev;
 
+bool xen_map_cache_enabled(void)
+{
+    /* Map cache enabled implies xen_enabled().  */
+    return xen_enabled() && mapcache;
+}
+
 static inline void mapcache_lock(MapCache *mc)
 {
     qemu_mutex_lock(&mc->lock);

hw/xen/xen_stubs.c

@@ -29,6 +29,11 @@ bool xen_mr_is_memory(MemoryRegion *mr)
     g_assert_not_reached();
 }
 
+bool xen_map_cache_enabled(void)
+{
+    return false;
+}
+
 void xen_invalidate_map_cache_entry(uint8_t *buffer)
 {
     g_assert_not_reached();

include/system/xen-mapcache.h

@@ -13,6 +13,7 @@
 
 typedef hwaddr (*phys_offset_to_gaddr_t)(hwaddr phys_offset,
                                          ram_addr_t size);
+bool xen_map_cache_enabled(void);
 void xen_map_cache_init(phys_offset_to_gaddr_t f,
                         void *opaque);
 uint8_t *xen_map_cache(MemoryRegion *mr, hwaddr phys_addr, hwaddr size,