created src/memory.rs for helping keep track of physical and virtual memory

1 files changed, 24 insertions, 0 deletions

diff --git a/StrixKernel/src/memory.rs b/StrixKernel/src/memory.rs
new file mode 100644
index 0000000..2493815
--- /dev/null
+++ b/StrixKernel/src/memory.rs
@@ -0,0 +1,24 @@
+use x86_64::{
+    structures::paging::PageTable,
+    VirtAddr,
+};
+
+/// Returns a mutable reference to the active level 4 table.
+///
+/// This function is unsafe because the caller must guarantee that the
+/// complete physical memory is mapped to virtual memory at the passed
+/// `physical_memory_offset`. Also, this function must be only called once
+/// to avoid aliasing `&mut` references (which is undefined behavior).
+pub unsafe fn active_level_4_table(physical_memory_offset: VirtAddr)
+    -> &'static mut PageTable
+{
+    use x86_64::registers::control::Cr3;
+
+    let (level_4_table_frame, _) = Cr3::read();
+
+    let phys = level_4_table_frame.start_address();
+    let virt = physical_memory_offset + phys.as_u64();
+    let page_table_ptr: *mut PageTable = virt.as_mut_ptr();
+
+    unsafe { &mut *page_table_ptr }
+}