vm-allocator: Add page size related functions

To avoid code duplication extract page related functions to their
own module and add utility functions for manipulating addresses
related to page sizes

Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>

vm-allocator/src/page_size.rs

@@ -0,0 +1,38 @@
+// Copyright 2023 Arm Limited (or its affiliates). All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+use libc::{sysconf, _SC_PAGESIZE};
+
+/// get host page size
+pub fn get_page_size() -> u64 {
+    // SAFETY: FFI call. Trivially safe.
+    unsafe { sysconf(_SC_PAGESIZE) as u64 }
+}
+
+/// round up address to let it align page size
+pub fn align_page_size_up(address: u64) -> u64 {
+    let page_size = get_page_size();
+    (address + page_size - 1) & !(page_size - 1)
+}
+
+/// round down address to let it align page size
+pub fn align_page_size_down(address: u64) -> u64 {
+    let page_size = get_page_size();
+    address & !(page_size - 1)
+}
+
+/// Test if address is 4k aligned
+pub fn is_4k_aligned(address: u64) -> bool {
+    (address & 0xfff) == 0
+}
+
+/// Test if size is 4k aligned
+pub fn is_4k_multiple(size: u64) -> bool {
+    (size & 0xfff) == 0
+}
+
+/// Test if address is page size aligned
+pub fn is_page_size_aligned(address: u64) -> bool {
+    let page_size = get_page_size();
+    address & (page_size - 1) == 0
+}