deallocate kernel stack

xernel/kernel/src/sched/process.rs

@@ -82,9 +82,6 @@ impl Process {
             );
         }
 
-        // TODO: how to unmap this stack later??
-        // We can't add it to Vm because it's not in the lower half of the address space
-
         stack_top
     }
 

xernel/kernel/src/sched/thread.rs

@@ -1,5 +1,10 @@
 use alloc::sync::Arc;
 use libxernel::sync::Spinlock;
+use x86_64::structures::paging::{Page, PageSize, PhysFrame, Size4KiB};
+
+use crate::mem::frame::FRAME_ALLOCATOR;
+use crate::mem::paging::KERNEL_PAGE_MAPPER;
+use crate::mem::STACK_SIZE;
 
 use super::context::CpuContext;
 use super::process::{Process, KERNEL_PROCESS};
@@ -167,3 +172,22 @@ impl Thread {
         self.process.upgrade()
     }
 }
+
+impl Drop for Thread {
+    fn drop(&mut self) {
+        if self.is_kernel_thread() {
+            let mut page_mapper = KERNEL_PAGE_MAPPER.lock();
+            let mut frame_allocator = FRAME_ALLOCATOR.lock();
+
+            for addr in (self.thread_stack..self.thread_stack + STACK_SIZE as usize).step_by(Size4KiB::SIZE as usize) {
+                unsafe {
+                    let page = Page::<Size4KiB>::from_start_address(VirtAddr::new(addr as u64)).unwrap();
+                    let phys_addr = page_mapper.translate(page.start_address()).unwrap();
+
+                    frame_allocator.deallocate_frame(PhysFrame::<Size4KiB>::containing_address(phys_addr));
+                    page_mapper.unmap(page.start_address());
+                }
+            }
+        }
+    }
+}