xen: Introduce the Xen mapcache

On IA32 host or IA32 PAE host, at present, generally, we can't create
an HVM guest with more than 2G memory, because generally it's almost
impossible for Qemu to find a large enough and consecutive virtual
address space to map an HVM guest's whole physical address space.
The attached patch fixes this issue using dynamic mapping based on
little blocks of memory.

Each call to qemu_get_ram_ptr makes a call to qemu_map_cache with the
lock option, so mapcache will not unmap these ram_ptr.

Blocks that do not belong to the RAM, but usually to a device ROM or to
a framebuffer, are handled in a separate function. So the whole RAMBlock
can be map.

Signed-off-by: Jun Nakajima <jun.nakajima@intel.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/hw/xen_common.h b/hw/xen_common.h
index 47b8afe..dd3e896 100644
--- a/hw/xen_common.h
+++ b/hw/xen_common.h
@@ -63,6 +63,15 @@
 }
 
 
+static inline int xc_domain_populate_physmap_exact
+    (XenXC xc_handle, uint32_t domid, unsigned long nr_extents,
+     unsigned int extent_order, unsigned int mem_flags, xen_pfn_t *extent_start)
+{
+    return xc_domain_memory_populate_physmap
+        (xc_handle, domid, nr_extents, extent_order, mem_flags, extent_start);
+}
+
+
 /* Xen 4.1 */
 #else