vm: implement a sparse memory model

vm/bootstrap.c

@@ -3,6 +3,7 @@
 #include <socks/vm.h>
 #include <socks/memblock.h>
 #include <socks/printk.h>
+#include <socks/machine/cpu.h>
 #include <stddef.h>
 #include <limits.h>
 #include <stdint.h>
@@ -18,8 +19,10 @@ kern_status_t vm_bootstrap(const vm_zone_descriptor_t *zones, size_t nr_zones)
 	node_data = memblock_alloc(sizeof(vm_pg_data_t) * numa_count, 8);
 	printk("vm: initialising %u node%s", numa_count, numa_count > 1 ? "s" : "");
 
-	vm_set_memory_model(VM_MODEL_FLAT);
-	vm_flat_init();
+	/* TODO select which memory model to use automatically, and add
+	   a kernel boot parameter to override the choice */
+	vm_set_memory_model(VM_MODEL_SPARSE);
+	vm_sparse_init();
 
 	for (size_t i = 0; i < nr_zones; i++) {
 		vm_zone_init(&node_data->pg_zones[zones[i].zd_id],  &zones[i]);