1 files changed, 144 insertions, 0 deletions
diff --git a/rust/kernel/pages.rs b/rust/kernel/pages.rs
new file mode 100644
index 000000000000..f2bb26810cd7
--- /dev/null
+++ b/rust/kernel/pages.rs
@@ -0,0 +1,144 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Kernel page allocation and management.
+//!
+//! TODO: This module is a work in progress.
+
+use crate::{
+    bindings, error::code::*, io_buffer::IoBufferReader, user_ptr::UserSlicePtrReader, Result,
+    PAGE_SIZE,
+};
+use core::{marker::PhantomData, ptr};
+
+/// A set of physical pages.
+///
+/// `Pages` holds a reference to a set of pages of order `ORDER`. Having the order as a generic
+/// const allows the struct to have the same size as a pointer.
+///
+/// # Invariants
+///
+/// The pointer `Pages::pages` is valid and points to 2^ORDER pages.
+pub struct Pages<const ORDER: u32> {
+    pub(crate) pages: *mut bindings::page,
+}
+
+impl<const ORDER: u32> Pages<ORDER> {
+    /// Allocates a new set of contiguous pages.
+    pub fn new() -> Result<Self> {
+        // TODO: Consider whether we want to allow callers to specify flags.
+        // SAFETY: This only allocates pages. We check that it succeeds in the next statement.
+        let pages = unsafe {
+            bindings::alloc_pages(
+                bindings::GFP_KERNEL | bindings::__GFP_ZERO | bindings::__GFP_HIGHMEM,
+                ORDER,
+            )
+        };
+        if pages.is_null() {
+            return Err(ENOMEM);
+        }
+        // INVARIANTS: We checked that the allocation above succeeded.
+        Ok(Self { pages })
+    }
+
+    /// Copies data from the given [`UserSlicePtrReader`] into the pages.
+    pub fn copy_into_page(
+        &self,
+        reader: &mut UserSlicePtrReader,
+        offset: usize,
+        len: usize,
+    ) -> Result {
+        // TODO: For now this only works on the first page.
+        let end = offset.checked_add(len).ok_or(EINVAL)?;
+        if end > PAGE_SIZE {
+            return Err(EINVAL);
+        }
+
+        let mapping = self.kmap(0).ok_or(EINVAL)?;
+
+        // SAFETY: We ensured that the buffer was valid with the check above.
+        unsafe { reader.read_raw((mapping.ptr as usize + offset) as _, len) }?;
+        Ok(())
+    }
+
+    /// Maps the pages and reads from them into the given buffer.
+    ///
+    /// # Safety
+    ///
+    /// Callers must ensure that the destination buffer is valid for the given length.
+    /// Additionally, if the raw buffer is intended to be recast, they must ensure that the data
+    /// can be safely cast; [`crate::io_buffer::ReadableFromBytes`] has more details about it.
+    pub unsafe fn read(&self, dest: *mut u8, offset: usize, len: usize) -> Result {
+        // TODO: For now this only works on the first page.
+        let end = offset.checked_add(len).ok_or(EINVAL)?;
+        if end > PAGE_SIZE {
+            return Err(EINVAL);
+        }
+
+        let mapping = self.kmap(0).ok_or(EINVAL)?;
+        unsafe { ptr::copy((mapping.ptr as *mut u8).add(offset), dest, len) };
+        Ok(())
+    }
+
+    /// Maps the pages and writes into them from the given buffer.
+    ///
+    /// # Safety
+    ///
+    /// Callers must ensure that the buffer is valid for the given length. Additionally, if the
+    /// page is (or will be) mapped by userspace, they must ensure that no kernel data is leaked
+    /// through padding if it was cast from another type; [`crate::io_buffer::WritableToBytes`] has
+    /// more details about it.
+    pub unsafe fn write(&self, src: *const u8, offset: usize, len: usize) -> Result {
+        // TODO: For now this only works on the first page.
+        let end = offset.checked_add(len).ok_or(EINVAL)?;
+        if end > PAGE_SIZE {
+            return Err(EINVAL);
+        }
+
+        let mapping = self.kmap(0).ok_or(EINVAL)?;
+        unsafe { ptr::copy(src, (mapping.ptr as *mut u8).add(offset), len) };
+        Ok(())
+    }
+
+    /// Maps the page at index `index`.
+    fn kmap(&self, index: usize) -> Option<PageMapping<'_>> {
+        if index >= 1usize << ORDER {
+            return None;
+        }
+
+        // SAFETY: We checked above that `index` is within range.
+        let page = unsafe { self.pages.add(index) };
+
+        // SAFETY: `page` is valid based on the checks above.
+        let ptr = unsafe { bindings::kmap(page) };
+        if ptr.is_null() {
+            return None;
+        }
+
+        Some(PageMapping {
+            page,
+            ptr,
+            _phantom: PhantomData,
+        })
+    }
+}
+
+impl<const ORDER: u32> Drop for Pages<ORDER> {
+    fn drop(&mut self) {
+        // SAFETY: By the type invariants, we know the pages are allocated with the given order.
+        unsafe { bindings::__free_pages(self.pages, ORDER) };
+    }
+}
+
+struct PageMapping<'a> {
+    page: *mut bindings::page,
+    ptr: *mut core::ffi::c_void,
+    _phantom: PhantomData<&'a i32>,
+}
+
+impl Drop for PageMapping<'_> {
+    fn drop(&mut self) {
+        // SAFETY: An instance of `PageMapping` is created only when `kmap` succeeded for the given
+        // page, so it is safe to unmap it here.
+        unsafe { bindings::kunmap(self.page) };
+    }
+}