patches/old/rust-maple_tree-add-mapletree.patch

From: Alice Ryhl <aliceryhl@google.com>
Subject: rust: maple_tree: add MapleTree
Date: Tue, 02 Sep 2025 08:35:11 +0000

Patch series "Add Rust abstraction for Maple Trees", v3.

This will be used in the Tyr driver [1] to allocate from the GPU's VA
space that is not owned by userspace, but by the kernel, for kernel GPU
mappings.

Danilo tells me that in nouveau, the maple tree is used for keeping track
of "VM regions" on top of GPUVM, and that he will most likely end up doing
the same in the Rust Nova driver as well.

These abstractions intentionally do not expose any way to make use of
external locking.  You are required to use the internal spinlock.  For
now, we do not support loads that only utilize rcu for protection.

This contains some parts taken from Andrew Ballance's RFC [2] from April. 
However, it has also been reworked significantly compared to that RFC
taking the use-cases in Tyr into account.


This patch (of 3):

The maple tree will be used in the Tyr driver to allocate and keep track
of GPU allocations created internally (i.e.  not by userspace).  It will
likely also be used in the Nova driver eventually.

This adds the simplest methods for additional and removal that do not
require any special care with respect to concurrency.

This implementation is based on the RFC by Andrew but with significant
changes to simplify the implementation.

[ojeda@kernel.org: fix intra-doc links]
  Link: https://lkml.kernel.org/r/20250910140212.997771-1-ojeda@kernel.org
Link: https://lkml.kernel.org/r/20250902-maple-tree-v3-0-fb5c8958fb1e@google.com
Link: https://lkml.kernel.org/r/20250902-maple-tree-v3-1-fb5c8958fb1e@google.com
Link: https://lore.kernel.org/r/20250627-tyr-v1-1-cb5f4c6ced46@collabora.com [1]
Link: https://lore.kernel.org/r/20250405060154.1550858-1-andrewjballance@gmail.com [2]
Co-developed-by: Andrew Ballance <andrewjballance@gmail.com>
Signed-off-by: Andrew Ballance <andrewjballance@gmail.com>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Danilo Krummrich <dakr@kernel.org>
Cc: Andreas Hindborg <a.hindborg@kernel.org>
Cc: Björn Roy Baron <bjorn3_gh@protonmail.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Daniel Almeida <daniel.almeida@collabora.com>
Cc: Gary Guo <gary@garyguo.net>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Trevor Gross <tmgross@umich.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 MAINTAINERS                |    4 
 include/linux/maple_tree.h |    3 
 rust/helpers/helpers.c     |    1 
 rust/helpers/maple_tree.c  |    8 
 rust/kernel/lib.rs         |    1 
 rust/kernel/maple_tree.rs  |  349 +++++++++++++++++++++++++++++++++++
 6 files changed, 366 insertions(+)

--- a/include/linux/maple_tree.h~rust-maple_tree-add-mapletree
+++ a/include/linux/maple_tree.h
@@ -481,6 +481,9 @@ struct ma_wr_state {
 #define MA_ERROR(err) \
 		((struct maple_enode *)(((unsigned long)err << 2) | 2UL))
 
+/*
+ * When changing MA_STATE, remember to also change rust/kernel/maple_tree.rs
+ */
 #define MA_STATE(name, mt, first, end)					\
 	struct ma_state name = {					\
 		.tree = mt,						\
--- a/MAINTAINERS~rust-maple_tree-add-mapletree
+++ a/MAINTAINERS
@@ -14672,6 +14672,8 @@ F:	net/mctp/
 
 MAPLE TREE
 M:	Liam R. Howlett <Liam.Howlett@oracle.com>
+R:	Alice Ryhl <aliceryhl@google.com>
+R:	Andrew Ballance <andrewjballance@gmail.com>
 L:	maple-tree@lists.infradead.org
 L:	linux-mm@kvack.org
 S:	Supported
@@ -14680,6 +14682,8 @@ F:	include/linux/maple_tree.h
 F:	include/trace/events/maple_tree.h
 F:	lib/maple_tree.c
 F:	lib/test_maple_tree.c
+F:	rust/helpers/maple_tree.c
+F:	rust/kernel/maple_tree.rs
 F:	tools/testing/radix-tree/maple.c
 F:	tools/testing/shared/linux/maple_tree.h
 
--- a/rust/helpers/helpers.c~rust-maple_tree-add-mapletree
+++ a/rust/helpers/helpers.c
@@ -26,6 +26,7 @@
 #include "io.c"
 #include "jump_label.c"
 #include "kunit.c"
+#include "maple_tree.c"
 #include "mm.c"
 #include "mutex.c"
 #include "of.c"
diff --git a/rust/helpers/maple_tree.c a/rust/helpers/maple_tree.c
new file mode 100644
--- /dev/null
+++ a/rust/helpers/maple_tree.c
@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/maple_tree.h>
+
+void rust_helper_mt_init_flags(struct maple_tree *mt, unsigned int flags)
+{
+	mt_init_flags(mt, flags);
+}
--- a/rust/kernel/lib.rs~rust-maple_tree-add-mapletree
+++ a/rust/kernel/lib.rs
@@ -96,6 +96,7 @@ pub mod jump_label;
 #[cfg(CONFIG_KUNIT)]
 pub mod kunit;
 pub mod list;
+pub mod maple_tree;
 pub mod miscdevice;
 pub mod mm;
 #[cfg(CONFIG_NET)]
diff --git a/rust/kernel/maple_tree.rs a/rust/kernel/maple_tree.rs
new file mode 100644
--- /dev/null
+++ a/rust/kernel/maple_tree.rs
@@ -0,0 +1,349 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Maple trees.
+//!
+//! C header: [`include/linux/maple_tree.h`](srctree/include/linux/maple_tree.h)
+//!
+//! Reference: <https://docs.kernel.org/core-api/maple_tree.html>
+
+use core::{
+    marker::PhantomData,
+    ops::{Bound, RangeBounds},
+    ptr,
+};
+
+use kernel::{
+    alloc::Flags,
+    error::to_result,
+    prelude::*,
+    types::{ForeignOwnable, Opaque},
+};
+
+/// A maple tree optimized for storing non-overlapping ranges.
+///
+/// # Invariants
+///
+/// Each range in the maple tree owns an instance of `T`.
+#[pin_data(PinnedDrop)]
+#[repr(transparent)]
+pub struct MapleTree<T: ForeignOwnable> {
+    #[pin]
+    tree: Opaque<bindings::maple_tree>,
+    _p: PhantomData<T>,
+}
+
+#[inline]
+fn to_maple_range(range: impl RangeBounds<usize>) -> Option<(usize, usize)> {
+    let first = match range.start_bound() {
+        Bound::Included(start) => *start,
+        Bound::Excluded(start) => start.checked_add(1)?,
+        Bound::Unbounded => 0,
+    };
+
+    let last = match range.end_bound() {
+        Bound::Included(end) => *end,
+        Bound::Excluded(end) => end.checked_sub(1)?,
+        Bound::Unbounded => usize::MAX,
+    };
+
+    if last < first {
+        return None;
+    }
+
+    Some((first, last))
+}
+
+impl<T: ForeignOwnable> MapleTree<T> {
+    /// Create a new maple tree.
+    ///
+    /// The tree will use the regular implementation with a higher branching factor, rather than
+    /// the allocation tree.
+    #[inline]
+    pub fn new() -> impl PinInit<Self> {
+        pin_init!(MapleTree {
+            // SAFETY: This initializes a maple tree into a pinned slot. The maple tree will be
+            // destroyed in Drop before the memory location becomes invalid.
+            tree <- Opaque::ffi_init(|slot| unsafe { bindings::mt_init_flags(slot, 0) }),
+            _p: PhantomData,
+        })
+    }
+
+    /// Insert the value at the given index.
+    ///
+    /// # Errors
+    ///
+    /// If the maple tree already contains a range using the given index, then this call will
+    /// return an [`InsertErrorKind::Occupied`]. It may also fail if memory allocation fails.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use kernel::maple_tree::{InsertErrorKind, MapleTree};
+    ///
+    /// let tree = KBox::pin_init(MapleTree::<KBox<i32>>::new(), GFP_KERNEL)?;
+    ///
+    /// let ten = KBox::new(10, GFP_KERNEL)?;
+    /// let twenty = KBox::new(20, GFP_KERNEL)?;
+    /// let the_answer = KBox::new(42, GFP_KERNEL)?;
+    ///
+    /// // These calls will succeed.
+    /// tree.insert(100, ten, GFP_KERNEL)?;
+    /// tree.insert(101, twenty, GFP_KERNEL)?;
+    ///
+    /// // This will fail because the index is already in use.
+    /// assert_eq!(
+    ///     tree.insert(100, the_answer, GFP_KERNEL).unwrap_err().cause,
+    ///     InsertErrorKind::Occupied,
+    /// );
+    /// # Ok::<_, Error>(())
+    /// ```
+    #[inline]
+    pub fn insert(&self, index: usize, value: T, gfp: Flags) -> Result<(), InsertError<T>> {
+        self.insert_range(index..=index, value, gfp)
+    }
+
+    /// Insert a value to the specified range, failing on overlap.
+    ///
+    /// This accepts the usual types of Rust ranges using the `..` and `..=` syntax for exclusive
+    /// and inclusive ranges respectively. The range must not be empty, and must not overlap with
+    /// any existing range.
+    ///
+    /// # Errors
+    ///
+    /// If the maple tree already contains an overlapping range, then this call will return an
+    /// [`InsertErrorKind::Occupied`]. It may also fail if memory allocation fails or if the
+    /// requested range is invalid (e.g. empty).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use kernel::maple_tree::{InsertErrorKind, MapleTree};
+    ///
+    /// let tree = KBox::pin_init(MapleTree::<KBox<i32>>::new(), GFP_KERNEL)?;
+    ///
+    /// let ten = KBox::new(10, GFP_KERNEL)?;
+    /// let twenty = KBox::new(20, GFP_KERNEL)?;
+    /// let the_answer = KBox::new(42, GFP_KERNEL)?;
+    /// let hundred = KBox::new(100, GFP_KERNEL)?;
+    ///
+    /// // Insert the value 10 at the indices 100 to 499.
+    /// tree.insert_range(100..500, ten, GFP_KERNEL)?;
+    ///
+    /// // Insert the value 20 at the indices 500 to 1000.
+    /// tree.insert_range(500..=1000, twenty, GFP_KERNEL)?;
+    ///
+    /// // This will fail due to overlap with the previous range on index 1000.
+    /// assert_eq!(
+    ///     tree.insert_range(1000..1200, the_answer, GFP_KERNEL).unwrap_err().cause,
+    ///     InsertErrorKind::Occupied,
+    /// );
+    ///
+    /// // When using .. to specify the range, you must be careful to ensure that the range is
+    /// // non-empty.
+    /// assert_eq!(
+    ///     tree.insert_range(72..72, hundred, GFP_KERNEL).unwrap_err().cause,
+    ///     InsertErrorKind::InvalidRequest,
+    /// );
+    /// # Ok::<_, Error>(())
+    /// ```
+    pub fn insert_range<R>(&self, range: R, value: T, gfp: Flags) -> Result<(), InsertError<T>>
+    where
+        R: RangeBounds<usize>,
+    {
+        let Some((first, last)) = to_maple_range(range) else {
+            return Err(InsertError {
+                value,
+                cause: InsertErrorKind::InvalidRequest,
+            });
+        };
+
+        let ptr = T::into_foreign(value);
+
+        // SAFETY: The tree is valid, and we are passing a pointer to an owned instance of `T`.
+        let res = to_result(unsafe {
+            bindings::mtree_insert_range(self.tree.get(), first, last, ptr, gfp.as_raw())
+        });
+
+        if let Err(err) = res {
+            // SAFETY: As `mtree_insert_range` failed, it is safe to take back ownership.
+            let value = unsafe { T::from_foreign(ptr) };
+
+            let cause = if err == ENOMEM {
+                InsertErrorKind::AllocError(kernel::alloc::AllocError)
+            } else if err == EEXIST {
+                InsertErrorKind::Occupied
+            } else {
+                InsertErrorKind::InvalidRequest
+            };
+            Err(InsertError { value, cause })
+        } else {
+            Ok(())
+        }
+    }
+
+    /// Erase the range containing the given index.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use kernel::maple_tree::MapleTree;
+    ///
+    /// let tree = KBox::pin_init(MapleTree::<KBox<i32>>::new(), GFP_KERNEL)?;
+    ///
+    /// let ten = KBox::new(10, GFP_KERNEL)?;
+    /// let twenty = KBox::new(20, GFP_KERNEL)?;
+    ///
+    /// tree.insert_range(100..500, ten, GFP_KERNEL)?;
+    /// tree.insert(67, twenty, GFP_KERNEL)?;
+    ///
+    /// assert_eq!(tree.erase(67).map(|v| *v), Some(20));
+    /// assert_eq!(tree.erase(275).map(|v| *v), Some(10));
+    ///
+    /// // The previous call erased the entire range, not just index 275.
+    /// assert!(tree.erase(127).is_none());
+    /// # Ok::<_, Error>(())
+    /// ```
+    #[inline]
+    pub fn erase(&self, index: usize) -> Option<T> {
+        // SAFETY: `self.tree` contains a valid maple tree.
+        let ret = unsafe { bindings::mtree_erase(self.tree.get(), index) };
+
+        // SAFETY: If the pointer is not null, then we took ownership of a valid instance of `T`
+        // from the tree.
+        unsafe { T::try_from_foreign(ret) }
+    }
+
+    /// Free all `T` instances in this tree.
+    ///
+    /// # Safety
+    ///
+    /// This frees Rust data referenced by the maple tree without removing it from the maple tree,
+    /// leaving it in an invalid state. The caller must ensure that this invalid state cannot be
+    /// observed by the end-user.
+    unsafe fn free_all_entries(self: Pin<&mut Self>) {
+        // SAFETY: The caller provides exclusive access to the entire maple tree, so we have
+        // exclusive access to the entire maple tree despite not holding the lock.
+        let mut ma_state = unsafe { MaState::new_raw(self.into_ref().get_ref(), 0, usize::MAX) };
+
+        loop {
+            // This uses the raw accessor because we're destroying pointers without removing them
+            // from the maple tree, which is only valid because this is the destructor.
+            let ptr = ma_state.mas_find_raw(usize::MAX);
+            if ptr.is_null() {
+                break;
+            }
+            // SAFETY: By the type invariants, this pointer references a valid value of type `T`.
+            // By the safety requirements, it is okay to free it without removing it from the maple
+            // tree.
+            drop(unsafe { T::from_foreign(ptr) });
+        }
+    }
+}
+
+#[pinned_drop]
+impl<T: ForeignOwnable> PinnedDrop for MapleTree<T> {
+    #[inline]
+    fn drop(mut self: Pin<&mut Self>) {
+        // We only iterate the tree if the Rust value has a destructor.
+        if core::mem::needs_drop::<T>() {
+            // SAFETY: Other than the below `mtree_destroy` call, the tree will not be accessed
+            // after this call.
+            unsafe { self.as_mut().free_all_entries() };
+        }
+
+        // SAFETY: The tree is valid, and will not be accessed after this call.
+        unsafe { bindings::mtree_destroy(self.tree.get()) };
+    }
+}
+
+/// A helper type used for navigating a [`MapleTree`].
+///
+/// # Invariants
+///
+/// For the duration of `'tree`:
+///
+/// * The `ma_state` references a valid `MapleTree<T>`.
+/// * The `ma_state` has read/write access to the tree.
+pub struct MaState<'tree, T: ForeignOwnable> {
+    state: bindings::ma_state,
+    _phantom: PhantomData<&'tree mut MapleTree<T>>,
+}
+
+impl<'tree, T: ForeignOwnable> MaState<'tree, T> {
+    /// Initialize a new `MaState` with the given tree.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that this `MaState` has read/write access to the maple tree.
+    #[inline]
+    unsafe fn new_raw(mt: &'tree MapleTree<T>, first: usize, end: usize) -> Self {
+        // INVARIANT:
+        // * Having a reference ensures that the `MapleTree<T>` is valid for `'tree`.
+        // * The caller ensures that we have read/write access.
+        Self {
+            state: bindings::ma_state {
+                tree: mt.tree.get(),
+                index: first,
+                last: end,
+                node: ptr::null_mut(),
+                status: bindings::maple_status_ma_start,
+                min: 0,
+                max: usize::MAX,
+                alloc: ptr::null_mut(),
+                mas_flags: 0,
+                store_type: bindings::store_type_wr_invalid,
+                ..Default::default()
+            },
+            _phantom: PhantomData,
+        }
+    }
+
+    #[inline]
+    fn as_raw(&mut self) -> *mut bindings::ma_state {
+        &raw mut self.state
+    }
+
+    #[inline]
+    fn mas_find_raw(&mut self, max: usize) -> *mut c_void {
+        // SAFETY: By the type invariants, the `ma_state` is active and we have read/write access
+        // to the tree.
+        unsafe { bindings::mas_find(self.as_raw(), max) }
+    }
+}
+
+/// Error type for failure to insert a new value.
+pub struct InsertError<T> {
+    /// The value that could not be inserted.
+    pub value: T,
+    /// The reason for the failure to insert.
+    pub cause: InsertErrorKind,
+}
+
+/// The reason for the failure to insert.
+#[derive(PartialEq, Eq, Copy, Clone, Debug)]
+pub enum InsertErrorKind {
+    /// There is already a value in the requested range.
+    Occupied,
+    /// Failure to allocate memory.
+    AllocError(kernel::alloc::AllocError),
+    /// The insertion request was invalid.
+    InvalidRequest,
+}
+
+impl From<InsertErrorKind> for Error {
+    #[inline]
+    fn from(kind: InsertErrorKind) -> Error {
+        match kind {
+            InsertErrorKind::Occupied => EEXIST,
+            InsertErrorKind::AllocError(kernel::alloc::AllocError) => ENOMEM,
+            InsertErrorKind::InvalidRequest => EINVAL,
+        }
+    }
+}
+
+impl<T> From<InsertError<T>> for Error {
+    #[inline]
+    fn from(insert_err: InsertError<T>) -> Error {
+        Error::from(insert_err.cause)
+    }
+}
_