Enable HIMEM in vexpress_gem5_serverconfig.
diff --git a/arch/arm/configs/vexpress_gem5_serverconfig b/arch/arm/configs/vexpress_gem5_serverconfig
index 406d497..feef59c 100644
--- a/arch/arm/configs/vexpress_gem5_serverconfig
+++ b/arch/arm/configs/vexpress_gem5_serverconfig
@@ -464,7 +464,7 @@
# CONFIG_ARCH_SPARSEMEM_DEFAULT is not set
# CONFIG_ARCH_SELECT_MEMORY_MODEL is not set
CONFIG_HAVE_ARCH_PFN_VALID=y
-# CONFIG_HIGHMEM is not set
+CONFIG_HIGHMEM=y
CONFIG_HW_PERF_EVENTS=y
CONFIG_FLATMEM=y
CONFIG_FLAT_NODE_MEM_MAP=y