feat: ring3

src/memory/stack.rs

@@ -0,0 +1,196 @@
+use crate::memory::{
+    AddressSpace, CachePolicy, FRAME_SIZE, FrameAllocator, MapError, OwnedFrame, PagePermissions,
+    VirtualAddr,
+};
+
+const STACK_PAGES: usize = 16;
+const STACK_SIZE: usize = STACK_PAGES * FRAME_SIZE;
+
+const KERNEL_STACK_TOP: VirtualAddr = VirtualAddr::new(0xFFFF_FFFE_0000_0000);
+const USER_STACK_TOP: VirtualAddr = VirtualAddr::new(0x0000_7FFF_FFFF_F000);
+
+#[derive(Debug)]
+pub enum StackCreateError {
+    AddressOverflow,
+    UnalignedStackTop,
+    OutOfFrames,
+    GuardPageMapped,
+    Map(MapError),
+}
+
+struct StackMapping {
+    guard_page: VirtualAddr,
+    mapped_start: VirtualAddr,
+    top: VirtualAddr,
+}
+
+impl StackMapping {
+    fn allocate(
+        address_space: &mut AddressSpace,
+        allocator: &mut FrameAllocator,
+        top: VirtualAddr,
+        permissions: PagePermissions,
+    ) -> Result<Self, StackCreateError> {
+        if top.as_usize() % FRAME_SIZE != 0 {
+            return Err(StackCreateError::UnalignedStackTop);
+        }
+
+        let mapped_start = VirtualAddr::new(
+            top.as_usize()
+                .checked_sub(STACK_SIZE)
+                .ok_or(StackCreateError::AddressOverflow)?,
+        );
+        let guard_page = VirtualAddr::new(
+            mapped_start
+                .as_usize()
+                .checked_sub(FRAME_SIZE)
+                .ok_or(StackCreateError::AddressOverflow)?,
+        );
+
+        if address_space.to_physical(guard_page).is_some() {
+            return Err(StackCreateError::GuardPageMapped);
+        }
+
+        let mut mapped_pages = 0;
+
+        while mapped_pages < STACK_PAGES {
+            let virtual_address = VirtualAddr::new(
+                mapped_start
+                    .as_usize()
+                    .checked_add(mapped_pages * FRAME_SIZE)
+                    .ok_or(StackCreateError::AddressOverflow)?,
+            );
+            let frame = match allocator.alloc() {
+                Some(frame) => frame,
+                None => {
+                    Self::rollback(address_space, allocator, mapped_start, mapped_pages);
+                    return Err(StackCreateError::OutOfFrames);
+                }
+            };
+
+            if let Err(error) = address_space.map(
+                frame.frame_address().start_address(),
+                virtual_address,
+                permissions,
+                allocator,
+                CachePolicy::WriteBack,
+            ) {
+                unsafe { allocator.dealloc(frame) };
+                Self::rollback(address_space, allocator, mapped_start, mapped_pages);
+                return Err(StackCreateError::Map(error));
+            }
+
+            let _ = frame.into_raw();
+            mapped_pages += 1;
+        }
+
+        debug_assert!(address_space.to_physical(guard_page).is_none());
+
+        Ok(Self {
+            guard_page,
+            mapped_start,
+            top,
+        })
+    }
+
+    fn rollback(
+        address_space: &mut AddressSpace,
+        allocator: &mut FrameAllocator,
+        mapped_start: VirtualAddr,
+        mapped_pages: usize,
+    ) {
+        for page in (0..mapped_pages).rev() {
+            let virtual_address = VirtualAddr::new(mapped_start.as_usize() + page * FRAME_SIZE);
+            let frame = unsafe {
+                address_space
+                    .unmap(virtual_address, allocator)
+                    .expect("failed to roll back stack mapping")
+            };
+            unsafe { allocator.dealloc(OwnedFrame::from_raw(frame)) };
+        }
+    }
+
+    /// # Safety
+    ///
+    /// The caller must ensure this stack is not active on any CPU and cannot be accessed by any
+    /// kernel operation while it is being destroyed.
+    unsafe fn destroy(self, address_space: &mut AddressSpace, allocator: &mut FrameAllocator) {
+        for page in (0..STACK_PAGES).rev() {
+            let virtual_address =
+                VirtualAddr::new(self.mapped_start.as_usize() + page * FRAME_SIZE);
+            let frame = unsafe {
+                address_space
+                    .unmap(virtual_address, allocator)
+                    .expect("stack mapping was unexpectedly missing")
+            };
+            unsafe { allocator.dealloc(OwnedFrame::from_raw(frame)) };
+        }
+
+        debug_assert!(address_space.to_physical(self.guard_page).is_none());
+    }
+}
+
+pub struct KernelStack {
+    mapping: StackMapping,
+}
+
+impl KernelStack {
+    pub fn allocate(
+        address_space: &mut AddressSpace,
+        allocator: &mut FrameAllocator,
+    ) -> Result<Self, StackCreateError> {
+        let mapping = StackMapping::allocate(
+            address_space,
+            allocator,
+            KERNEL_STACK_TOP,
+            PagePermissions::new(true, false, false),
+        )?;
+
+        Ok(Self { mapping })
+    }
+
+    pub const fn top(&self) -> VirtualAddr {
+        self.mapping.top
+    }
+
+    /// # Safety
+    ///
+    /// The caller must ensure this stack is not active on any CPU and cannot be accessed by any
+    /// kernel operation while it is being destroyed.
+    pub unsafe fn destroy(self, address_space: &mut AddressSpace, allocator: &mut FrameAllocator) {
+        unsafe { self.mapping.destroy(address_space, allocator) };
+    }
+}
+
+pub struct UserStack {
+    mapping: StackMapping,
+}
+
+impl UserStack {
+    pub fn allocate(
+        address_space: &mut AddressSpace,
+        allocator: &mut FrameAllocator,
+    ) -> Result<Self, StackCreateError> {
+        let top = VirtualAddr::new(USER_STACK_TOP.as_usize());
+        let mapping = StackMapping::allocate(
+            address_space,
+            allocator,
+            top,
+            PagePermissions::new(true, false, true),
+        )?;
+
+        Ok(Self { mapping })
+    }
+
+    pub const fn top(&self) -> VirtualAddr {
+        self.mapping.top
+    }
+
+    /// # Safety
+    ///
+    /// The caller must ensure this stack is not active in any thread and cannot be accessed while
+    /// it is being destroyed.
+    pub unsafe fn destroy(self, address_space: &mut AddressSpace, allocator: &mut FrameAllocator) {
+        unsafe { self.mapping.destroy(address_space, allocator) };
+    }
+}