[PATCH v3 0/7] rust: Add Per-CPU Variable API

[PATCH v3 0/7] rust: Add Per-CPU Variable API

[Mitchell Levy]

This series adds an API for declaring an using per-CPU variables from
Rust, and it also adds support for Rust access to C per-CPU variables
(subject to some soundness requirements). It also adds a small sample
module, samples/rust/rust_percpu.rs, in the vein of lib/percpu_test.c.

---
Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>

---
Changes in v3:
- Add a `CheckedPerCpuToken` that enables usage of per-CPU variables via
  a `&T`, allowing for a wholly safe interface when `T` allows for
  interior mutability (Thanks Benno Lossin)
- Add support for non-zeroable types to be used in a `DynamicPerCpu`.
- Remove necessity for `unsafe` to get a `StaticPerCpu` from its
  declaration (Thanks Benno Lossin)
- Allow the declaration of static per-CPU variables of types that are
  `!Sync`.
- Implement `PerCpuPtr` in terms of `MaybeUninit<T>` rather than `T` so
  as to keep all invariants in the `DynamicPerCpu` and `StaticPerCpu`
  types --- this would also enable `PerCpuPtr` to be used in a per-CPU
  type that does lazy initialization.
- Link to v2: https://lore.kernel.org/r/20250712-rust-percpu-v2-0-826f2567521b@gmail.com

Changes in v2:
- Fix kernel test robot issues
- Fix documentation error
- Require `T: Zeroable` in the dynamic case
- Link to v1: https://lore.kernel.org/r/20250624-rust-percpu-v1-0-9c59b07d2a9c@gmail.com

Changes in v1:
- Use wrapping_add in `PerCpuPtr::get_ref` since overflow is expected.
- Separate the dynamic and static cases, with shared logic in a
  `PerCpuPtr` type.
- Implement pin-hole optimizations for numeric types
- Don't assume `GFP_KERNEL` when allocating the `Arc` in the dynamic
  case.
- Link to RFC v2: https://lore.kernel.org/r/20250414-rust-percpu-v2-0-5ea0d0de13a5@gmail.com

Changes in RFC v2:
- Renamed PerCpuVariable to StaticPerCpuSymbol to be more descriptive
- Support dynamically allocated per-CPU variables via the
  PerCpuAllocation type. Rework statically allocated variables to use
  this new type.
- Make use of a token/closure-based API via the PerCpu and PerCpuToken
  types, rather than an API based on PerCpuRef that automatically
  Deref(Mut)'s into a &(mut) T.
- Rebased
- Link to RFC: https://lore.kernel.org/r/20241219-rust-percpu-v1-0-209117e822b1@gmail.com

---
Mitchell Levy (7):
      rust: percpu: introduce a rust API for per-CPU variables
      rust: percpu: add a rust per-CPU variable sample
      rust: cpumask: Add a `Cpumask` iterator
      rust: cpumask: Add getters for globally defined cpumasks
      rust: percpu: Support non-zeroable types for DynamicPerCpu
      rust: percpu: Add pin-hole optimizations for numerics
      rust: percpu: cache per-CPU pointers in the dynamic case

 rust/helpers/cpumask.c          |   5 +
 rust/helpers/helpers.c          |   2 +
 rust/helpers/percpu.c           |  20 +++
 rust/helpers/preempt.c          |  14 ++
 rust/kernel/cpumask.rs          |  94 ++++++++++++-
 rust/kernel/lib.rs              |   3 +
 rust/kernel/percpu.rs           | 239 +++++++++++++++++++++++++++++++++
 rust/kernel/percpu/cpu_guard.rs |  35 +++++
 rust/kernel/percpu/dynamic.rs   | 127 ++++++++++++++++++
 rust/kernel/percpu/numeric.rs   | 128 ++++++++++++++++++
 rust/kernel/percpu/static_.rs   | 132 +++++++++++++++++++
 samples/rust/Kconfig            |   9 ++
 samples/rust/Makefile           |   1 +
 samples/rust/rust_percpu.rs     | 284 ++++++++++++++++++++++++++++++++++++++++
 14 files changed, 1092 insertions(+), 1 deletion(-)
---
base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585
change-id: 20240813-rust-percpu-ea2f54b5da33

Best regards,
-- 
Mitchell Levy <levymitchell0@gmail.com>

[PATCH v3 1/7] rust: percpu: introduce a rust API for per-CPU variables

[Mitchell Levy]

Per-CPU variables are an important tool for reducing lock contention,
especially in systems with many processors. They also provide a
convenient way to handle data that are logically associated with a
particular CPU (e.g., the currently running task). Therefore, add a Rust
API to make use of per-CPU variables.

Add a `CpuGuard` type that disables preemption for its lifetime. Add a
`PerCpuAllocation` type used to track dynamic allocations. Add a
`define_per_cpu!` macro to create static per-CPU allocations. Add
`DynamicPerCpu` and `StaticPerCpu` to provide a high-level API. Add a
`PerCpu` trait to unify the dynamic and static cases.

Co-developed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>
---
 rust/helpers/helpers.c          |   2 +
 rust/helpers/percpu.c           |   9 ++
 rust/helpers/preempt.c          |  14 +++
 rust/kernel/lib.rs              |   3 +
 rust/kernel/percpu.rs           | 223 ++++++++++++++++++++++++++++++++++++++++
 rust/kernel/percpu/cpu_guard.rs |  35 +++++++
 rust/kernel/percpu/dynamic.rs   |  83 +++++++++++++++
 rust/kernel/percpu/static_.rs   | 132 ++++++++++++++++++++++++
 8 files changed, 501 insertions(+)

diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 7cf7fe95e41d..2fc8d26cfe66 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -31,9 +31,11 @@
 #include "of.c"
 #include "page.c"
 #include "pci.c"
+#include "percpu.c"
 #include "pid_namespace.c"
 #include "platform.c"
 #include "poll.c"
+#include "preempt.c"
 #include "property.c"
 #include "rbtree.c"
 #include "rcu.c"
diff --git a/rust/helpers/percpu.c b/rust/helpers/percpu.c
new file mode 100644
index 000000000000..a091389f730f
--- /dev/null
+++ b/rust/helpers/percpu.c
@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/percpu.h>
+
+void __percpu *rust_helper_alloc_percpu(size_t sz, size_t align)
+{
+	return __alloc_percpu(sz, align);
+}
+
diff --git a/rust/helpers/preempt.c b/rust/helpers/preempt.c
new file mode 100644
index 000000000000..2c7529528ddd
--- /dev/null
+++ b/rust/helpers/preempt.c
@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/preempt.h>
+
+void rust_helper_preempt_disable(void)
+{
+	preempt_disable();
+}
+
+void rust_helper_preempt_enable(void)
+{
+	preempt_enable();
+}
+
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index ed53169e795c..ed0d5756dc55 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -106,6 +106,9 @@
 pub mod page;
 #[cfg(CONFIG_PCI)]
 pub mod pci;
+// Only x86_64 is supported by percpu for now
+#[cfg(CONFIG_X86_64)]
+pub mod percpu;
 pub mod pid_namespace;
 pub mod platform;
 pub mod prelude;
diff --git a/rust/kernel/percpu.rs b/rust/kernel/percpu.rs
new file mode 100644
index 000000000000..35afcdba3ccd
--- /dev/null
+++ b/rust/kernel/percpu.rs
@@ -0,0 +1,223 @@
+// SPDX-License-Identifier: GPL-2.0
+//! This module contains abstractions for creating and using per-CPU variables from Rust.
+//! See the define_per_cpu! macro and the DynamicPerCpu<T> type, as well as the PerCpu<T> trait.
+
+pub mod cpu_guard;
+mod dynamic;
+mod static_;
+
+#[doc(inline)]
+pub use dynamic::*;
+#[doc(inline)]
+pub use static_::*;
+
+use bindings::{alloc_percpu, free_percpu};
+
+use crate::alloc::Flags;
+use crate::percpu::cpu_guard::CpuGuard;
+use crate::prelude::*;
+use crate::sync::Arc;
+use crate::types::Opaque;
+use crate::{declare_extern_per_cpu, get_static_per_cpu};
+
+use core::arch::asm;
+use core::cell::{Cell, RefCell, UnsafeCell};
+use core::mem::{align_of, size_of, MaybeUninit};
+
+use ffi::c_void;
+
+/// A per-CPU pointer; that is, an offset into the per-CPU area. Note that this type is NOT a smart
+/// pointer, it does not manage the allocation.
+pub struct PerCpuPtr<T>(*mut MaybeUninit<T>);
+
+/// Represents exclusive access to the memory location pointed at by a particular PerCpu<T>.
+pub struct PerCpuToken<'a, T> {
+    // INVARIANT: the current CPU's memory location associated with the per-CPU variable pointed at
+    // by `ptr` (i.e., the entry in the per-CPU area on the current CPU) has been initialized.
+    _guard: CpuGuard,
+    ptr: &'a PerCpuPtr<T>,
+}
+
+/// Represents access to the memory location pointed at by a particular PerCpu<T> where the type
+/// `T` manages access to the underlying memory to avoid aliaising troubles. (For example, `T`
+/// might be a `Cell` or `RefCell`.)
+pub struct CheckedPerCpuToken<'a, T> {
+    // INVARIANT: the current CPU's memory location associated with the per-CPU variable pointed at
+    // by `ptr` (i.e., the entry in the per-CPU area on the current CPU) has been initialized.
+    _guard: CpuGuard,
+    ptr: &'a PerCpuPtr<T>,
+}
+
+impl<T> PerCpuPtr<T> {
+    /// Makes a new PerCpuPtr from a raw per-CPU pointer.
+    ///
+    /// # Safety
+    /// `ptr` must be a valid per-CPU pointer.
+    pub unsafe fn new(ptr: *mut MaybeUninit<T>) -> Self {
+        Self(ptr)
+    }
+
+    /// Get a `&mut MaybeUninit<T>` to the per-CPU variable on the current CPU represented by `&self`
+    ///
+    /// # Safety
+    /// The returned `&mut T` must follow Rust's aliasing rules. That is, no other `&(mut) T` may
+    /// exist that points to the same location in memory. In practice, this means that `get_(mut_)ref`
+    /// must not be called on another `PerCpuPtr<T>` that is a copy/clone of `&self` for as long as
+    /// the returned reference lives.
+    ///
+    /// CPU preemption must be disabled before calling this function and for the lifetime of the
+    /// returned reference. Otherwise, the returned reference might end up being a reference to a
+    /// different CPU's per-CPU area, causing the potential for a data race.
+    #[allow(clippy::mut_from_ref)] // Safety requirements prevent aliasing issues
+    pub unsafe fn get_mut_ref(&self) -> &mut MaybeUninit<T> {
+        // SAFETY: `self.get_ptr()` returns a valid pointer to a `MaybeUninit<T>` by its contract,
+        // and the safety requirements of this function ensure that the returned reference is
+        // exclusive.
+        unsafe { &mut *(self.get_ptr()) }
+    }
+
+    /// Get a `&MaybeUninit<T>` to the per-CPU variable on the current CPU represented by `&self`
+    ///
+    /// # Safety
+    /// The returned `&T` must follow Rust's aliasing rules. That is, no `&mut T` may exist that
+    /// points to the same location in memory. In practice, this means that `get_mut_ref` must not
+    /// be called on another `PerCpuPtr<T>` that is a copy/clone of `&self` for as long as the
+    /// returned reference lives.
+    ///
+    /// CPU preemption must be disabled before calling this function and for the lifetime of the
+    /// returned reference. Otherwise, the returned reference might end up being a reference to a
+    /// different CPU's per-CPU area, causing the potential for a data race.
+    pub unsafe fn get_ref(&self) -> &MaybeUninit<T> {
+        // SAFETY: `self.get_ptr()` returns a valid pointer to a `MaybeUninit<T>` by its contract.
+        // The safety requirements of this function ensure that the returned reference isn't
+        // aliased by a `&mut MaybeUninit<T>`.
+        unsafe { &*self.get_ptr() }
+    }
+
+    /// Get a `*mut MaybeUninit<T>` to the per-CPU variable on the current CPU represented by
+    /// `&self`. Note that if CPU preemption is not disabled before calling this function, use of
+    /// the returned pointer may cause a data race without some other synchronization mechanism.
+    /// Buyer beware!
+    pub fn get_ptr(&self) -> *mut MaybeUninit<T> {
+        let this_cpu_off_pcpu: PerCpuPtr<*mut c_void> = get_static_per_cpu!(this_cpu_off).0;
+        let mut this_cpu_area: *mut c_void;
+        // SAFETY: gs + this_cpu_off_pcpu is guaranteed to be a valid pointer because `gs` points
+        // to the per-CPU area and this_cpu_off_pcpu is a valid per-CPU allocation.
+        unsafe {
+            asm!(
+                "mov {out}, gs:[{off_val}]",
+                off_val = in(reg) this_cpu_off_pcpu.0,
+                out = out(reg) this_cpu_area,
+            )
+        };
+
+        // This_cpu_area + self.0 is guaranteed to be a valid pointer by the per-CPU subsystem and
+        // the invariant that self.0 is a valid offset into the per-CPU area.
+        (this_cpu_area).wrapping_add(self.0 as usize).cast()
+    }
+}
+
+// SAFETY: Sending a `PerCpuPtr<T>` to another thread is safe because as soon as it's sent, the
+// pointer is logically referring to a different place in memory in the other CPU's per-CPU area.
+// In particular, this means that there are no restrictions on the type `T`.
+unsafe impl<T> Send for PerCpuPtr<T> {}
+
+// SAFETY: Two threads concurrently making use of a `PerCpuPtr<T>` will each see the `T` in their
+// own per-CPU area, so there's no potential for a data race (regardless of whether `T` is itself
+// `Sync`).
+unsafe impl<T> Sync for PerCpuPtr<T> {}
+
+impl<T> Clone for PerCpuPtr<T> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+/// `PerCpuPtr` is just a wrapper around a pointer.
+impl<T> Copy for PerCpuPtr<T> {}
+
+/// A trait representing a per-CPU variable. This is implemented for both `StaticPerCpu<T>` and
+/// `DynamicPerCpu<T>`. The main usage of this trait is to call `get_mut` to get a `PerCpuToken`
+/// that can be used to access the underlying per-CPU variable. See `PerCpuToken::with`.
+pub trait PerCpu<T> {
+    /// Produces a token, asserting that the holder has exclusive access to the underlying memory
+    /// pointed to by `self`
+    ///
+    /// # Safety
+    /// No other `PerCpuToken` or `CheckedPerCpuToken` may exist on the current CPU (which is a
+    /// sensible notion, since we keep a `CpuGuard` around) that is derived from the same
+    /// `PerCpu<T>` or a clone thereof.
+    unsafe fn get_mut(&mut self, guard: CpuGuard) -> PerCpuToken<'_, T>;
+}
+
+/// A marker trait for types that are interior mutable. Types that implement this trait can be used
+/// to create "checked" per-CPU variables. See `CheckedPerCpu<T>`.
+pub trait InteriorMutable {}
+
+impl<T> InteriorMutable for Cell<T> {}
+impl<T> InteriorMutable for RefCell<T> {}
+impl<T> InteriorMutable for UnsafeCell<T> {}
+impl<T> InteriorMutable for Opaque<T> {}
+
+/// A trait representing a per-CPU variable that is usable via a `&T`. The unsafety of `PerCpu<T>`
+/// stems from the fact that the holder of a `PerCpuToken` can use it to get a `&mut T` to the
+/// underlying per-CPU variable. This is problematic because the existence of aliaising `&mut T` is
+/// undefined behavior in Rust. This type avoids that issue by only allowing access via a `&T`,
+/// with the tradeoff that then `T` must be interior mutable or the underlying per-CPU variable
+/// must be a constant for the lifetime of the corresponding `CheckedPerCpu<T>`.
+///
+/// Currently, only the case where `T` is interior mutable has first-class support, though a custom
+/// implementation of `PerCpu<T>`/`CheckedPerCpu<T>` could be created for the const case.
+pub trait CheckedPerCpu<T>: PerCpu<T> {
+    /// Produces a token via which the holder can access the underlying per-CPU variable.
+    fn get(&mut self, guard: CpuGuard) -> CheckedPerCpuToken<'_, T>;
+}
+
+impl<'a, T> PerCpuToken<'a, T> {
+    /// # Safety
+    /// No other `PerCpuToken` or `CheckedPerCpuToken` may exist on the current CPU (which is a
+    /// sensible notion, since we keep a `CpuGuard` around) that uses the same `PerCpuPtr<T>`.
+    ///
+    /// The current CPU's memory location associated with the per-CPU variable pointed at by `ptr`
+    /// (i.e., the entry in the per-CPU area on this CPU) must be initialized.
+    pub unsafe fn new(guard: CpuGuard, ptr: &'a PerCpuPtr<T>) -> PerCpuToken<'a, T> {
+        Self { _guard: guard, ptr }
+    }
+
+    /// Immediately invokes `func` with a `&mut T` that points at the underlying per-CPU variable
+    /// that `&mut self` represents.
+    pub fn with<U>(&mut self, func: U)
+    where
+        U: FnOnce(&mut T),
+    {
+        // SAFETY: The existence of a PerCpuToken means that the requirements for get_mut_ref are
+        // satisfied. Likewise, the requirements for assume_init_mut are satisfied because the
+        // invariants of this type ensure that on the current CPU (which is a sensible notion
+        // because we have a CpuGuard), the memory location pointed to by `ptr` is initialized.
+        func(unsafe { self.ptr.get_mut_ref().assume_init_mut() });
+    }
+}
+
+impl<'a, T> CheckedPerCpuToken<'a, T> {
+    /// # Safety
+    /// The current CPU's memory location associated with the per-CPU variable pointed at by `ptr`
+    /// (i.e., the entry in the per-CPU area on this CPU) must be initialized.
+    pub unsafe fn new(guard: CpuGuard, ptr: &'a PerCpuPtr<T>) -> CheckedPerCpuToken<'a, T> {
+        Self { _guard: guard, ptr }
+    }
+
+    /// Immediately invokes `func` with a `&T` that points at the underlying per-CPU variable that
+    /// `&mut self` represents.
+    pub fn with<U>(&mut self, func: U)
+    where
+        U: FnOnce(&T),
+    {
+        // SAFETY: The existence of a CheckedPerCpuToken means that the requirements for get_ref
+        // are satisfied. Likewise, the requirements for assume_init_ref are satisfied because the
+        // invariants of this type ensure that on the current CPU (which is a sensible notion
+        // because we have a CpuGuard), the memory location pointed to by `ptr` is initialized.
+        func(unsafe { self.ptr.get_ref().assume_init_ref() });
+    }
+}
+
+declare_extern_per_cpu!(this_cpu_off: *mut c_void);
diff --git a/rust/kernel/percpu/cpu_guard.rs b/rust/kernel/percpu/cpu_guard.rs
new file mode 100644
index 000000000000..14c04b12e7f0
--- /dev/null
+++ b/rust/kernel/percpu/cpu_guard.rs
@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: GPL-2.0
+//! Contains abstractions for disabling CPU preemption. See `CpuGuard`.
+
+/// A RAII guard for bindings::preempt_disable and bindings::preempt_enable. Guarantees preemption
+/// is disabled for as long as this object exists.
+pub struct CpuGuard {
+    // Don't make one without using new()
+    _phantom: (),
+}
+
+impl CpuGuard {
+    /// Create a new CpuGuard. Disables preemption for its lifetime.
+    pub fn new() -> Self {
+        // SAFETY: There are no preconditions required to call preempt_disable
+        unsafe {
+            bindings::preempt_disable();
+        }
+        CpuGuard { _phantom: () }
+    }
+}
+
+impl Default for CpuGuard {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl Drop for CpuGuard {
+    fn drop(&mut self) {
+        // SAFETY: There are no preconditions required to call preempt_enable
+        unsafe {
+            bindings::preempt_enable();
+        }
+    }
+}
diff --git a/rust/kernel/percpu/dynamic.rs b/rust/kernel/percpu/dynamic.rs
new file mode 100644
index 000000000000..ce95e420f943
--- /dev/null
+++ b/rust/kernel/percpu/dynamic.rs
@@ -0,0 +1,83 @@
+// SPDX-License-Identifier: GPL-2.0
+//! Dynamically allocated per-CPU variables.
+
+use super::*;
+
+/// Represents a dynamic allocation of a per-CPU variable via alloc_percpu. Calls free_percpu when
+/// dropped.
+pub struct PerCpuAllocation<T>(PerCpuPtr<T>);
+
+impl<T: Zeroable> PerCpuAllocation<T> {
+    /// Dynamically allocates a space in the per-CPU area suitably sized and aligned to hold a `T`,
+    /// initially filled with the zero value for `T`.
+    ///
+    /// Returns `None` under the same circumstances the C function `alloc_percpu` returns `NULL`.
+    pub fn new_zero() -> Option<PerCpuAllocation<T>> {
+        let ptr: *mut MaybeUninit<T> =
+            // SAFETY: No preconditions to call alloc_percpu; MaybeUninit<T> is
+            // `#[repr(transparent)]`, so we can cast a `*mut T` to it.
+            unsafe { alloc_percpu(size_of::<T>(), align_of::<T>()) }.cast();
+        if ptr.is_null() {
+            return None;
+        }
+
+        // alloc_percpu returns zero'ed memory
+        Some(Self(PerCpuPtr(ptr)))
+    }
+}
+
+impl<T> PerCpuAllocation<T> {
+    /// Makes a per-CPU allocation sized and aligned to hold a `T`.
+    ///
+    /// Returns `None` under the same circumstances the C function `alloc_percpu` returns `NULL`.
+    pub fn new_uninit() -> Option<PerCpuAllocation<T>> {
+        let ptr: *mut MaybeUninit<T> =
+            // SAFETY: No preconditions to call alloc_percpu; MaybeUninit<T> is
+            // `#[repr(transparent)]`, so we can cast a `*mut T` to it.
+            unsafe { alloc_percpu(size_of::<T>(), align_of::<T>()) }.cast();
+        if ptr.is_null() {
+            return None;
+        }
+
+        Some(Self(PerCpuPtr(ptr)))
+    }
+}
+
+impl<T> Drop for PerCpuAllocation<T> {
+    fn drop(&mut self) {
+        // SAFETY: self.0.0 was returned by alloc_percpu, and so was a valid pointer into
+        // the percpu area, and has remained valid by the invariants of PerCpuAllocation<T>.
+        unsafe { free_percpu(self.0 .0.cast()) }
+    }
+}
+
+/// Holds a dynamically-allocated per-CPU variable.
+#[derive(Clone)]
+pub struct DynamicPerCpu<T> {
+    // INVARIANT: The memory location in each CPU's per-CPU area pointed at by `alloc.0` has been
+    // initialized.
+    pub(super) alloc: Arc<PerCpuAllocation<T>>,
+}
+
+impl<T: Zeroable> DynamicPerCpu<T> {
+    /// Allocates a new per-CPU variable
+    ///
+    /// # Arguments
+    /// * `flags` - Flags used to allocate an `Arc` that keeps track of the underlying
+    ///   `PerCpuAllocation`.
+    pub fn new_zero(flags: Flags) -> Option<Self> {
+        let alloc: PerCpuAllocation<T> = PerCpuAllocation::new_zero()?;
+
+        let arc = Arc::new(alloc, flags).ok()?;
+
+        Some(Self { alloc: arc })
+    }
+}
+
+impl<T> PerCpu<T> for DynamicPerCpu<T> {
+    unsafe fn get_mut(&mut self, guard: CpuGuard) -> PerCpuToken<'_, T> {
+        // SAFETY: The requirements of `PerCpu::get_mut` and this type's invariant ensure that the
+        // requirements of `PerCpuToken::new` are met.
+        unsafe { PerCpuToken::new(guard, &self.alloc.0) }
+    }
+}
diff --git a/rust/kernel/percpu/static_.rs b/rust/kernel/percpu/static_.rs
new file mode 100644
index 000000000000..be226dd2c3aa
--- /dev/null
+++ b/rust/kernel/percpu/static_.rs
@@ -0,0 +1,132 @@
+// SPDX-License-Identifier: GPL-2.0
+//! Statically allocated per-CPU variables.
+
+use super::*;
+
+/// A wrapper used for declaring static per-CPU variables. These symbols are "virtual" in that the
+/// linker uses them to generate offsets into each CPU's per-CPU area, but shouldn't be read
+/// from/written to directly. The fact that the statics are immutable prevents them being written
+/// to (generally), this struct having _val be non-public prevents reading from them.
+///
+/// The end-user of the per-CPU API should make use of the define_per_cpu! macro instead of
+/// declaring variables of this type directly. All instances of this type must be `static` and
+/// `#[link_section = ".data..percpu"]` (which the macro handles).
+#[repr(transparent)]
+pub struct StaticPerCpuSymbol<T> {
+    _val: T, // generate a correctly sized type
+}
+
+/// Holds a statically-allocated per-CPU variable.
+#[derive(Clone)]
+pub struct StaticPerCpu<T>(pub(super) PerCpuPtr<T>);
+
+impl<T> StaticPerCpu<T> {
+    /// Creates a `StaticPerCpu<T>` from a `StaticPerCpuSymbol<T>`. You should probably be using
+    /// `get_static_per_cpu!` instead.
+    pub fn new(ptr: *const StaticPerCpuSymbol<T>) -> StaticPerCpu<T> {
+        // SAFETY: `StaticPerCpuSymbol<T>` is `#[repr(transparent)]`, so we can safely cast a
+        // pointer to it into a pointer to `MaybeUninit<T>`. The validity of it as a per-CPU
+        // pointer is guaranteed by the per-CPU subsystem and invariants of the StaticPerCpuSymbol
+        // type.
+        let pcpu_ptr = unsafe { PerCpuPtr::new(ptr.cast_mut().cast()) };
+        Self(pcpu_ptr)
+    }
+}
+
+impl<T> PerCpu<T> for StaticPerCpu<T> {
+    unsafe fn get_mut(&mut self, guard: CpuGuard) -> PerCpuToken<'_, T> {
+        // SAFETY: The requirements of `PerCpu::get_mut` and the fact that statically-allocated
+        // per-CPU variables are initialized by the per-CPU subsystem ensure that the requirements
+        // of `PerCpuToken::new` are met.
+        unsafe { PerCpuToken::new(guard, &self.0) }
+    }
+}
+
+impl<T: InteriorMutable> CheckedPerCpu<T> for StaticPerCpu<T> {
+    fn get(&mut self, guard: CpuGuard) -> CheckedPerCpuToken<'_, T> {
+        // SAFETY: The per-CPU subsystem guarantees that each CPU's instance of a
+        // statically allocated variable begins with a copy of the contents of the
+        // corresponding symbol in `.data..percpu`. Thus, the requirements of
+        // `CheckedPerCpuToken::new` are met.
+        unsafe { CheckedPerCpuToken::new(guard, &self.0) }
+    }
+}
+
+/// Gets a `StaticPerCpu<T>` from a symbol declared with `define_per_cpu!` or
+/// `declare_extern_per_cpu!`.
+///
+/// # Arguments
+/// * `ident` - The identifier declared
+#[macro_export]
+macro_rules! get_static_per_cpu {
+    ($id:ident) => {
+        $crate::percpu::StaticPerCpu::new((&raw const $id).cast())
+    };
+}
+
+/// Declares a StaticPerCpuSymbol corresponding to a per-CPU variable defined in C. Be sure to read
+/// the safety requirements of `PerCpu::get`.
+#[macro_export]
+macro_rules! declare_extern_per_cpu {
+    ($id:ident: $ty:ty) => {
+        extern "C" {
+            static $id: StaticPerCpuSymbol<$ty>;
+        }
+    };
+}
+
+/// define_per_cpu! is analogous to the C DEFINE_PER_CPU macro in that it lets you create a
+/// statically allocated per-CPU variable.
+///
+/// # Example
+/// ```
+/// use kernel::define_per_cpu;
+/// use kernel::percpu::StaticPerCpuSymbol;
+///
+/// define_per_cpu!(pub MY_PERCPU: u64 = 0);
+/// ```
+#[macro_export]
+macro_rules! define_per_cpu {
+    ($vis:vis $id:ident: $ty:ty = $expr:expr) => {
+        $crate::macros::paste! {
+            // We might want to have a per-CPU variable that doesn't implement `Sync` (not paying
+            // sync overhead costs is part of the point), but Rust won't let us declare a static of
+            // a `!Sync` type. Of course, we don't actually have any synchronization issues, since
+            // each CPU will see its own copy of the variable, so we cheat a little bit and tell
+            // Rust it's fine.
+            #[doc(hidden)]
+            #[allow(non_camel_case_types)]
+            #[repr(transparent)] // It needs to be the same size as $ty
+            struct [<__PRIVATE_TYPE_ $id>]($ty);
+
+            impl [<__PRIVATE_TYPE_ $id>] {
+                #[doc(hidden)]
+                const fn new(val: $ty) -> Self {
+                    Self(val)
+                }
+            }
+
+            // Expand $expr outside of the unsafe block to avoid silently allowing unsafe code to be
+            // used without a user-facing unsafe block
+            #[doc(hidden)]
+            static [<__INIT_ $id>]: [<__PRIVATE_TYPE_ $id>] = [<__PRIVATE_TYPE_ $id>]::new($expr);
+
+            // SAFETY: This type will ONLY ever be used to declare a `StaticPerCpuSymbol`
+            // (which we then only ever use as input to `&raw`). Reading from the symbol is
+            // already UB, so we won't ever actually have any variables of this type where
+            // synchronization is a concern.
+            #[doc(hidden)]
+            unsafe impl Sync for [<__PRIVATE_TYPE_ $id>] {}
+
+            // SAFETY: StaticPerCpuSymbol<T> is #[repr(transparent)], so we can freely convert from
+            // [<__PRIVATE_TYPE_ $id>], which is also `#[repr(transparent)]` (i.e., everything is
+            // just a `$ty` from a memory layout perspective).
+            #[link_section = ".data..percpu"]
+            $vis static $id: StaticPerCpuSymbol<[<__PRIVATE_TYPE_ $id>]> = unsafe {
+                core::mem::transmute_copy::<
+                    [<__PRIVATE_TYPE_ $id>], StaticPerCpuSymbol<[<__PRIVATE_TYPE_ $id>]>
+                >(&[<__INIT_ $id>])
+            };
+        }
+    };
+}

-- 
2.34.1

[PATCH v3 2/7] rust: percpu: add a rust per-CPU variable sample

[Mitchell Levy]

Add a short exercise for Rust's per-CPU variable API, modelled after
lib/percpu_test.c

Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>
---
 rust/helpers/percpu.c       |   6 ++
 samples/rust/Kconfig        |   9 +++
 samples/rust/Makefile       |   1 +
 samples/rust/rust_percpu.rs | 163 ++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 179 insertions(+)

diff --git a/rust/helpers/percpu.c b/rust/helpers/percpu.c
index a091389f730f..8cc01d094752 100644
--- a/rust/helpers/percpu.c
+++ b/rust/helpers/percpu.c
@@ -1,9 +1,15 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include <linux/percpu.h>
+#include <linux/smp.h>
 
 void __percpu *rust_helper_alloc_percpu(size_t sz, size_t align)
 {
 	return __alloc_percpu(sz, align);
 }
 
+void rust_helper_on_each_cpu(smp_call_func_t func, void *info, int wait)
+{
+	on_each_cpu(func, info, wait);
+}
+
diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig
index 7f7371a004ee..23e35d64ac78 100644
--- a/samples/rust/Kconfig
+++ b/samples/rust/Kconfig
@@ -105,6 +105,15 @@ config SAMPLE_RUST_DRIVER_AUXILIARY
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_PERCPU
+	tristate "Per-CPU support"
+	depends on m
+	help
+	  Enable this option to build a module which demonstrates Rust per-CPU
+	  operations.
+
+	  If unsure, say N.
+
 config SAMPLE_RUST_HOSTPROGS
 	bool "Host programs"
 	help
diff --git a/samples/rust/Makefile b/samples/rust/Makefile
index bd2faad63b4f..8a34d9d74754 100644
--- a/samples/rust/Makefile
+++ b/samples/rust/Makefile
@@ -10,6 +10,7 @@ obj-$(CONFIG_SAMPLE_RUST_DRIVER_PLATFORM)	+= rust_driver_platform.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_FAUX)		+= rust_driver_faux.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_AUXILIARY)	+= rust_driver_auxiliary.o
 obj-$(CONFIG_SAMPLE_RUST_CONFIGFS)		+= rust_configfs.o
+obj-$(CONFIG_SAMPLE_RUST_PERCPU)		+= rust_percpu.o
 
 rust_print-y := rust_print_main.o rust_print_events.o
 
diff --git a/samples/rust/rust_percpu.rs b/samples/rust/rust_percpu.rs
new file mode 100644
index 000000000000..98ca1c781b6b
--- /dev/null
+++ b/samples/rust/rust_percpu.rs
@@ -0,0 +1,163 @@
+// SPDX-License-Identifier: GPL-2.0
+//! A simple demonstration of the rust per-CPU API.
+
+use core::cell::RefCell;
+use core::ffi::c_void;
+
+use kernel::{
+    bindings::on_each_cpu,
+    cpu::CpuId,
+    define_per_cpu, get_static_per_cpu,
+    percpu::{cpu_guard::*, *},
+    pr_info,
+    prelude::*,
+};
+
+module! {
+    type: PerCpuMod,
+    name: "rust_percpu",
+    authors: ["Mitchell Levy"],
+    description: "Sample to demonstrate the Rust per-CPU API",
+    license: "GPL v2",
+}
+
+struct PerCpuMod;
+
+define_per_cpu!(PERCPU: i64 = 0);
+define_per_cpu!(UPERCPU: u64 = 0);
+define_per_cpu!(CHECKED: RefCell<u64> = RefCell::new(0));
+
+impl kernel::Module for PerCpuMod {
+    fn init(_module: &'static ThisModule) -> Result<Self, Error> {
+        pr_info!("rust percpu test start\n");
+
+        let mut native: i64 = 0;
+        let mut pcpu: StaticPerCpu<i64> = get_static_per_cpu!(PERCPU);
+
+        // SAFETY: We only have one PerCpu that points at PERCPU
+        unsafe { pcpu.get_mut(CpuGuard::new()) }.with(|val: &mut i64| {
+            pr_info!("The contents of pcpu are {}\n", val);
+
+            native += -1;
+            *val += -1;
+            pr_info!("Native: {}, *pcpu: {}\n", native, val);
+            assert!(native == *val && native == -1);
+
+            native += 1;
+            *val += 1;
+            pr_info!("Native: {}, *pcpu: {}\n", native, val);
+            assert!(native == *val && native == 0);
+        });
+
+        let mut unative: u64 = 0;
+        let mut upcpu: StaticPerCpu<u64> = get_static_per_cpu!(UPERCPU);
+
+        // SAFETY: We only have one PerCpu pointing at UPERCPU
+        unsafe { upcpu.get_mut(CpuGuard::new()) }.with(|val: &mut u64| {
+            unative += 1;
+            *val += 1;
+            pr_info!("Unative: {}, *upcpu: {}\n", unative, val);
+            assert!(unative == *val && unative == 1);
+
+            unative = unative.wrapping_add((-1i64) as u64);
+            *val = val.wrapping_add((-1i64) as u64);
+            pr_info!("Unative: {}, *upcpu: {}\n", unative, val);
+            assert!(unative == *val && unative == 0);
+
+            unative = unative.wrapping_add((-1i64) as u64);
+            *val = val.wrapping_add((-1i64) as u64);
+            pr_info!("Unative: {}, *upcpu: {}\n", unative, val);
+            assert!(unative == *val && unative == (-1i64) as u64);
+
+            unative = 0;
+            *val = 0;
+
+            unative = unative.wrapping_sub(1);
+            *val = val.wrapping_sub(1);
+            pr_info!("Unative: {}, *upcpu: {}\n", unative, val);
+            assert!(unative == *val && unative == (-1i64) as u64);
+            assert!(unative == *val && unative == u64::MAX);
+        });
+
+        let mut checked_native: u64 = 0;
+        let mut checked: StaticPerCpu<RefCell<u64>> = get_static_per_cpu!(CHECKED);
+        checked.get(CpuGuard::new()).with(|val: &RefCell<u64>| {
+            checked_native += 1;
+            *val.borrow_mut() += 1;
+            pr_info!(
+                "Checked native: {}, *checked: {}\n",
+                checked_native,
+                val.borrow()
+            );
+            assert!(checked_native == *val.borrow() && checked_native == 1);
+
+            checked_native = checked_native.wrapping_add((-1i64) as u64);
+            val.replace_with(|old: &mut u64| old.wrapping_add((-1i64) as u64));
+            pr_info!(
+                "Checked native: {}, *checked: {}\n",
+                checked_native,
+                val.borrow()
+            );
+            assert!(checked_native == *val.borrow() && checked_native == 0);
+
+            checked_native = checked_native.wrapping_add((-1i64) as u64);
+            val.replace_with(|old: &mut u64| old.wrapping_add((-1i64) as u64));
+            pr_info!(
+                "Checked native: {}, *checked: {}\n",
+                checked_native,
+                val.borrow()
+            );
+            assert!(checked_native == *val.borrow() && checked_native == (-1i64) as u64);
+
+            checked_native = 0;
+            *val.borrow_mut() = 0;
+
+            checked_native = checked_native.wrapping_sub(1);
+            val.replace_with(|old: &mut u64| old.wrapping_sub(1));
+            pr_info!(
+                "Checked native: {}, *checked: {}\n",
+                checked_native,
+                val.borrow()
+            );
+            assert!(checked_native == *val.borrow() && checked_native == (-1i64) as u64);
+            assert!(checked_native == *val.borrow() && checked_native == u64::MAX);
+        });
+
+        pr_info!("rust static percpu test done\n");
+
+        pr_info!("rust dynamic percpu test start\n");
+        let mut test: DynamicPerCpu<u64> = DynamicPerCpu::new_zero(GFP_KERNEL).unwrap();
+
+        // SAFETY: No prerequisites for on_each_cpu.
+        unsafe {
+            on_each_cpu(Some(inc_percpu), (&raw mut test).cast(), 0);
+            on_each_cpu(Some(inc_percpu), (&raw mut test).cast(), 0);
+            on_each_cpu(Some(inc_percpu), (&raw mut test).cast(), 0);
+            on_each_cpu(Some(inc_percpu), (&raw mut test).cast(), 1);
+            on_each_cpu(Some(check_percpu), (&raw mut test).cast(), 1);
+        }
+
+        pr_info!("rust dynamic percpu test done\n");
+
+        // Return Err to unload the module
+        Result::Err(EINVAL)
+    }
+}
+
+extern "C" fn inc_percpu(info: *mut c_void) {
+    // SAFETY: We know that info is a void *const DynamicPerCpu<u64> and DynamicPerCpu<u64> is Send.
+    let mut pcpu = unsafe { (*(info as *const DynamicPerCpu<u64>)).clone() };
+    pr_info!("Incrementing on {}\n", CpuId::current().as_u32());
+
+    // SAFETY: We don't have multiple clones of pcpu in scope
+    unsafe { pcpu.get_mut(CpuGuard::new()) }.with(|val: &mut u64| *val += 1);
+}
+
+extern "C" fn check_percpu(info: *mut c_void) {
+    // SAFETY: We know that info is a void *const DynamicPerCpu<u64> and DynamicPerCpu<u64> is Send.
+    let mut pcpu = unsafe { (*(info as *const DynamicPerCpu<u64>)).clone() };
+    pr_info!("Asserting on {}\n", CpuId::current().as_u32());
+
+    // SAFETY: We don't have multiple clones of pcpu in scope
+    unsafe { pcpu.get_mut(CpuGuard::new()) }.with(|val: &mut u64| assert!(*val == 4));
+}

-- 
2.34.1

[PATCH v3 3/7] rust: cpumask: Add a `Cpumask` iterator

[Mitchell Levy]

Add an iterator for `Cpumask` making use of C's `cpumask_next`.

Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>
---
 rust/helpers/cpumask.c |  5 +++++
 rust/kernel/cpumask.rs | 48 +++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 52 insertions(+), 1 deletion(-)

diff --git a/rust/helpers/cpumask.c b/rust/helpers/cpumask.c
index eb10598a0242..d95bfa111191 100644
--- a/rust/helpers/cpumask.c
+++ b/rust/helpers/cpumask.c
@@ -42,6 +42,11 @@ bool rust_helper_cpumask_full(struct cpumask *srcp)
 	return cpumask_full(srcp);
 }
 
+unsigned int rust_helper_cpumask_next(int n, struct cpumask *srcp)
+{
+	return cpumask_next(n, srcp);
+}
+
 unsigned int rust_helper_cpumask_weight(struct cpumask *srcp)
 {
 	return cpumask_weight(srcp);
diff --git a/rust/kernel/cpumask.rs b/rust/kernel/cpumask.rs
index 3fcbff438670..b7401848f59e 100644
--- a/rust/kernel/cpumask.rs
+++ b/rust/kernel/cpumask.rs
@@ -6,7 +6,7 @@
 
 use crate::{
     alloc::{AllocError, Flags},
-    cpu::CpuId,
+    cpu::{self, CpuId},
     prelude::*,
     types::Opaque,
 };
@@ -161,6 +161,52 @@ pub fn copy(&self, dstp: &mut Self) {
     }
 }
 
+/// Iterator for a `Cpumask`.
+pub struct CpumaskIter<'a> {
+    mask: &'a Cpumask,
+    last: Option<u32>,
+}
+
+impl<'a> CpumaskIter<'a> {
+    /// Creates a new `CpumaskIter` for the given `Cpumask`.
+    fn new(mask: &'a Cpumask) -> CpumaskIter<'a> {
+        Self { mask, last: None }
+    }
+}
+
+impl<'a> Iterator for CpumaskIter<'a> {
+    type Item = CpuId;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        // SAFETY: By the type invariant, `self.mask.as_raw` is a `struct cpumask *`.
+        let next = unsafe {
+            bindings::cpumask_next(
+                if let Some(last) = self.last {
+                    last.try_into().unwrap()
+                } else {
+                    -1
+                },
+                self.mask.as_raw(),
+            )
+        };
+
+        if next == cpu::nr_cpu_ids() {
+            None
+        } else {
+            self.last = Some(next);
+            // SAFETY: `cpumask_next` returns either `nr_cpu_ids` or a valid CPU ID.
+            unsafe { Some(CpuId::from_u32_unchecked(next)) }
+        }
+    }
+}
+
+impl Cpumask {
+    /// Returns an iterator over the set bits in the cpumask.
+    pub fn iter(&self) -> CpumaskIter<'_> {
+        CpumaskIter::new(self)
+    }
+}
+
 /// A CPU Mask pointer.
 ///
 /// Rust abstraction for the C `struct cpumask_var_t`.

-- 
2.34.1

[PATCH v3 4/7] rust: cpumask: Add getters for globally defined cpumasks

[Mitchell Levy]

Add getters for the global cpumasks documented in
`include/linux/cpumask.h`, specifically:
- cpu_possible_mask
- cpu_online_mask
- cpu_enabled_mask
- cpu_present_mask
- cpu_active_mask

Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>
---
 rust/kernel/cpumask.rs | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/rust/kernel/cpumask.rs b/rust/kernel/cpumask.rs
index b7401848f59e..ca9aa6875b4a 100644
--- a/rust/kernel/cpumask.rs
+++ b/rust/kernel/cpumask.rs
@@ -77,6 +77,52 @@ pub unsafe fn as_ref<'a>(ptr: *const bindings::cpumask) -> &'a Self {
         unsafe { &*ptr.cast() }
     }
 
+    /// Get a CPU mask representing possible CPUs; has bit `cpu` set iff cpu is populatable
+    #[inline]
+    pub fn possible() -> &'static Self {
+        // SAFETY: `__cpu_possible_mask` is a valid global provided by the kernel that lives
+        // forever.
+        unsafe { Cpumask::as_ref(&raw const bindings::__cpu_possible_mask) }
+    }
+
+    /// Get a CPU mask representing online CPUs; has bit `cpu` set iff cpu available to the
+    /// scheduler
+    #[inline]
+    pub fn online() -> &'static Self {
+        // SAFETY: `__cpu_online_mask` is a valid global provided by the kernel that lives forever.
+        // Since we wrap the returned pointer in an `Opaque`, it's ok that `__cpu_online_mask`
+        // may change its value.
+        unsafe { Cpumask::as_ref(&raw const bindings::__cpu_online_mask) }
+    }
+
+    /// Get a CPU mask representing enabled CPUs; has bit `cpu` set iff cpu can be brought online
+    #[inline]
+    pub fn enabled() -> &'static Self {
+        // SAFETY: `__cpu_enabled_mask` is a valid global provided by the kernel that lives forever.
+        // Since we wrap the returned pointer in an `Opaque`, it's ok that `__cpu_enabled_mask`
+        // may change its value.
+        unsafe { Cpumask::as_ref(&raw const bindings::__cpu_enabled_mask) }
+    }
+
+    /// Get a CPU mask representing present CPUs; has bit `cpu` set iff cpu is populated
+    #[inline]
+    pub fn present() -> &'static Self {
+        // SAFETY: `__cpu_present_mask` is a valid global provided by the kernel that lives
+        // forever. Since we wrap the returned pointer in an `Opaque`, it's ok that
+        // `__cpu_present_mask` may change its value.
+        unsafe { Cpumask::as_ref(&raw const bindings::__cpu_present_mask) }
+    }
+
+    /// Get a CPU mask representing active CPUs; has bit `cpu` set iff cpu is available to
+    /// migration.
+    #[inline]
+    pub fn active() -> &'static Self {
+        // SAFETY: `__cpu_active_mask` is a valid global provided by the kernel that lives forever.
+        // Since we wrap the returned pointer in an `Opaque`, it's ok that `__cpu_active_mask`
+        // may change its value.
+        unsafe { Cpumask::as_ref(&raw const bindings::__cpu_active_mask) }
+    }
+
     /// Obtain the raw `struct cpumask` pointer.
     pub fn as_raw(&self) -> *mut bindings::cpumask {
         let this: *const Self = self;

-- 
2.34.1

[PATCH v3 5/7] rust: percpu: Support non-zeroable types for DynamicPerCpu

[Mitchell Levy]

Add functionality to `PerCpuPtr` to compute pointers to per-CPU variable
slots on other CPUs. Use this facility to initialize per-CPU variables
on all possible CPUs when a dynamic per-CPU variable is created with a
non-zeroable type. Since `RefCell` and other `Cell`-like types fall into
this category, `impl CheckedPerCpu` on `DynamicPerCpu` for these
`InteriorMutable` types since they can now be used. Add examples of
these usages to `samples/rust/rust_percpu.rs`.

Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>
---
 rust/helpers/percpu.c         |  5 +++
 rust/kernel/percpu.rs         | 15 +++++++
 rust/kernel/percpu/dynamic.rs | 40 +++++++++++++++++
 samples/rust/rust_percpu.rs   | 99 ++++++++++++++++++++++++++++++++++++++++---
 4 files changed, 152 insertions(+), 7 deletions(-)

diff --git a/rust/helpers/percpu.c b/rust/helpers/percpu.c
index 8cc01d094752..8d83b6b86106 100644
--- a/rust/helpers/percpu.c
+++ b/rust/helpers/percpu.c
@@ -8,6 +8,11 @@ void __percpu *rust_helper_alloc_percpu(size_t sz, size_t align)
 	return __alloc_percpu(sz, align);
 }
 
+void *rust_helper_per_cpu_ptr(void __percpu *ptr, unsigned int cpu)
+{
+	return per_cpu_ptr(ptr, cpu);
+}
+
 void rust_helper_on_each_cpu(smp_call_func_t func, void *info, int wait)
 {
 	on_each_cpu(func, info, wait);
diff --git a/rust/kernel/percpu.rs b/rust/kernel/percpu.rs
index 35afcdba3ccd..c68c7520b67f 100644
--- a/rust/kernel/percpu.rs
+++ b/rust/kernel/percpu.rs
@@ -14,6 +14,7 @@
 use bindings::{alloc_percpu, free_percpu};
 
 use crate::alloc::Flags;
+use crate::cpu::CpuId;
 use crate::percpu::cpu_guard::CpuGuard;
 use crate::prelude::*;
 use crate::sync::Arc;
@@ -115,6 +116,20 @@ pub fn get_ptr(&self) -> *mut MaybeUninit<T> {
         // the invariant that self.0 is a valid offset into the per-CPU area.
         (this_cpu_area).wrapping_add(self.0 as usize).cast()
     }
+
+    /// Get a `*mut MaybeUninit<T>` to the per-CPU variable on the CPU represented by `cpu`. Note
+    /// that without some kind of synchronization, use of the returned pointer may cause a data
+    /// race. It is the caller's responsibility to use the returned pointer in a reasonable way.
+    ///
+    /// # Safety
+    /// - The returned pointer is valid only if `self` is (that is, it points to a live allocation
+    ///   correctly sized and aligned to hold a `T`)
+    /// - The returned pointer is valid only if the bit corresponding to `cpu` is set in
+    ///   `Cpumask::possible()`.
+    pub unsafe fn get_remote_ptr(&self, cpu: CpuId) -> *mut MaybeUninit<T> {
+        // SAFETY: The requirements of this function ensure this call is safe.
+        unsafe { bindings::per_cpu_ptr(self.0.cast(), cpu.as_u32()) }.cast()
+    }
 }
 
 // SAFETY: Sending a `PerCpuPtr<T>` to another thread is safe because as soon as it's sent, the
diff --git a/rust/kernel/percpu/dynamic.rs b/rust/kernel/percpu/dynamic.rs
index ce95e420f943..64f04cef3705 100644
--- a/rust/kernel/percpu/dynamic.rs
+++ b/rust/kernel/percpu/dynamic.rs
@@ -3,6 +3,8 @@
 
 use super::*;
 
+use crate::cpumask::Cpumask;
+
 /// Represents a dynamic allocation of a per-CPU variable via alloc_percpu. Calls free_percpu when
 /// dropped.
 pub struct PerCpuAllocation<T>(PerCpuPtr<T>);
@@ -74,6 +76,36 @@ pub fn new_zero(flags: Flags) -> Option<Self> {
     }
 }
 
+impl<T: Clone> DynamicPerCpu<T> {
+    /// Allocates a new per-CPU variable
+    ///
+    /// # Arguments
+    /// * `val` - The initial value of the per-CPU variable on all CPUs.
+    /// * `flags` - Flags used to allocate an `Arc` that keeps track of the underlying
+    ///   `PerCpuAllocation`.
+    pub fn new_with(val: T, flags: Flags) -> Option<Self> {
+        let alloc: PerCpuAllocation<T> = PerCpuAllocation::new_uninit()?;
+        let ptr = alloc.0;
+
+        for cpu in Cpumask::possible().iter() {
+            // SAFETY: `ptr` is a valid allocation, and `cpu` appears in `Cpumask::possible()`
+            let remote_ptr = unsafe { ptr.get_remote_ptr(cpu) };
+            // SAFETY: Each CPU's slot corresponding to `ptr` is currently uninitialized, and no
+            // one else has a reference to it. Therefore, we can freely write to it without
+            // worrying about the need to drop what was there or whether we're racing with someone
+            // else. `PerCpuPtr::get_remote_ptr` guarantees that the pointer is valid since we
+            // derived it from a valid allocation and `cpu`.
+            unsafe {
+                (*remote_ptr).write(val.clone());
+            }
+        }
+
+        let arc = Arc::new(alloc, flags).ok()?;
+
+        Some(Self { alloc: arc })
+    }
+}
+
 impl<T> PerCpu<T> for DynamicPerCpu<T> {
     unsafe fn get_mut(&mut self, guard: CpuGuard) -> PerCpuToken<'_, T> {
         // SAFETY: The requirements of `PerCpu::get_mut` and this type's invariant ensure that the
@@ -81,3 +113,11 @@ unsafe fn get_mut(&mut self, guard: CpuGuard) -> PerCpuToken<'_, T> {
         unsafe { PerCpuToken::new(guard, &self.alloc.0) }
     }
 }
+
+impl<T: InteriorMutable> CheckedPerCpu<T> for DynamicPerCpu<T> {
+    fn get(&mut self, guard: CpuGuard) -> CheckedPerCpuToken<'_, T> {
+        // SAFETY: By the invariant of `DynamicPerCpu`, the memory location in each CPU's
+        // per-CPU area corresponding to this variable has been initialized.
+        unsafe { CheckedPerCpuToken::new(guard, &self.alloc.0) }
+    }
+}
diff --git a/samples/rust/rust_percpu.rs b/samples/rust/rust_percpu.rs
index 98ca1c781b6b..06b322019134 100644
--- a/samples/rust/rust_percpu.rs
+++ b/samples/rust/rust_percpu.rs
@@ -130,13 +130,72 @@ fn init(_module: &'static ThisModule) -> Result<Self, Error> {
 
         // SAFETY: No prerequisites for on_each_cpu.
         unsafe {
-            on_each_cpu(Some(inc_percpu), (&raw mut test).cast(), 0);
-            on_each_cpu(Some(inc_percpu), (&raw mut test).cast(), 0);
-            on_each_cpu(Some(inc_percpu), (&raw mut test).cast(), 0);
-            on_each_cpu(Some(inc_percpu), (&raw mut test).cast(), 1);
-            on_each_cpu(Some(check_percpu), (&raw mut test).cast(), 1);
+            on_each_cpu(Some(inc_percpu_u64), (&raw mut test).cast(), 0);
+            on_each_cpu(Some(inc_percpu_u64), (&raw mut test).cast(), 0);
+            on_each_cpu(Some(inc_percpu_u64), (&raw mut test).cast(), 0);
+            on_each_cpu(Some(inc_percpu_u64), (&raw mut test).cast(), 1);
+            on_each_cpu(Some(check_percpu_u64), (&raw mut test).cast(), 1);
         }
 
+        let mut checked: DynamicPerCpu<RefCell<u64>> =
+            DynamicPerCpu::new_with(RefCell::new(100), GFP_KERNEL).unwrap();
+
+        // SAFETY: No prerequisites for on_each_cpu.
+        unsafe {
+            on_each_cpu(Some(inc_percpu_refcell_u64), (&raw mut checked).cast(), 0);
+            on_each_cpu(Some(inc_percpu_refcell_u64), (&raw mut checked).cast(), 0);
+            on_each_cpu(Some(inc_percpu_refcell_u64), (&raw mut checked).cast(), 0);
+            on_each_cpu(Some(inc_percpu_refcell_u64), (&raw mut checked).cast(), 1);
+            on_each_cpu(Some(check_percpu_refcell_u64), (&raw mut checked).cast(), 1);
+        }
+
+        checked.get(CpuGuard::new()).with(|val: &RefCell<u64>| {
+            assert!(*val.borrow() == 104);
+
+            let mut checked_native = 0;
+            *val.borrow_mut() = 0;
+
+            checked_native += 1;
+            *val.borrow_mut() += 1;
+            pr_info!(
+                "Checked native: {}, *checked: {}\n",
+                checked_native,
+                val.borrow()
+            );
+            assert!(checked_native == *val.borrow() && checked_native == 1);
+
+            checked_native = checked_native.wrapping_add((-1i64) as u64);
+            val.replace_with(|old: &mut u64| old.wrapping_add((-1i64) as u64));
+            pr_info!(
+                "Checked native: {}, *checked: {}\n",
+                checked_native,
+                val.borrow()
+            );
+            assert!(checked_native == *val.borrow() && checked_native == 0);
+
+            checked_native = checked_native.wrapping_add((-1i64) as u64);
+            val.replace_with(|old: &mut u64| old.wrapping_add((-1i64) as u64));
+            pr_info!(
+                "Checked native: {}, *checked: {}\n",
+                checked_native,
+                val.borrow()
+            );
+            assert!(checked_native == *val.borrow() && checked_native == (-1i64) as u64);
+
+            checked_native = 0;
+            *val.borrow_mut() = 0;
+
+            checked_native = checked_native.wrapping_sub(1);
+            val.replace_with(|old: &mut u64| old.wrapping_sub(1));
+            pr_info!(
+                "Checked native: {}, *checked: {}\n",
+                checked_native,
+                val.borrow()
+            );
+            assert!(checked_native == *val.borrow() && checked_native == (-1i64) as u64);
+            assert!(checked_native == *val.borrow() && checked_native == u64::MAX);
+        });
+
         pr_info!("rust dynamic percpu test done\n");
 
         // Return Err to unload the module
@@ -144,7 +203,7 @@ fn init(_module: &'static ThisModule) -> Result<Self, Error> {
     }
 }
 
-extern "C" fn inc_percpu(info: *mut c_void) {
+extern "C" fn inc_percpu_u64(info: *mut c_void) {
     // SAFETY: We know that info is a void *const DynamicPerCpu<u64> and DynamicPerCpu<u64> is Send.
     let mut pcpu = unsafe { (*(info as *const DynamicPerCpu<u64>)).clone() };
     pr_info!("Incrementing on {}\n", CpuId::current().as_u32());
@@ -153,7 +212,7 @@ extern "C" fn inc_percpu(info: *mut c_void) {
     unsafe { pcpu.get_mut(CpuGuard::new()) }.with(|val: &mut u64| *val += 1);
 }
 
-extern "C" fn check_percpu(info: *mut c_void) {
+extern "C" fn check_percpu_u64(info: *mut c_void) {
     // SAFETY: We know that info is a void *const DynamicPerCpu<u64> and DynamicPerCpu<u64> is Send.
     let mut pcpu = unsafe { (*(info as *const DynamicPerCpu<u64>)).clone() };
     pr_info!("Asserting on {}\n", CpuId::current().as_u32());
@@ -161,3 +220,29 @@ extern "C" fn check_percpu(info: *mut c_void) {
     // SAFETY: We don't have multiple clones of pcpu in scope
     unsafe { pcpu.get_mut(CpuGuard::new()) }.with(|val: &mut u64| assert!(*val == 4));
 }
+
+extern "C" fn inc_percpu_refcell_u64(info: *mut c_void) {
+    // SAFETY: We know that info is a void *const DynamicPerCpu<RefCell<u64>> and
+    // DynamicPerCpu<RefCell<u64>> is Send.
+    let mut pcpu = unsafe { (*(info as *const DynamicPerCpu<RefCell<u64>>)).clone() };
+    // SAFETY: smp_processor_id has no preconditions
+    pr_info!("Incrementing on {}\n", CpuId::current().as_u32());
+
+    pcpu.get(CpuGuard::new()).with(|val: &RefCell<u64>| {
+        let mut val = val.borrow_mut();
+        *val += 1;
+    });
+}
+
+extern "C" fn check_percpu_refcell_u64(info: *mut c_void) {
+    // SAFETY: We know that info is a void *const DynamicPerCpu<RefCell<u64>> and
+    // DynamicPerCpu<RefCell<u64>> is Send.
+    let mut pcpu = unsafe { (*(info as *const DynamicPerCpu<RefCell<u64>>)).clone() };
+    // SAFETY: smp_processor_id has no preconditions
+    pr_info!("Asserting on {}\n", CpuId::current().as_u32());
+
+    pcpu.get(CpuGuard::new()).with(|val: &RefCell<u64>| {
+        let val = val.borrow();
+        assert!(*val == 104);
+    });
+}

-- 
2.34.1

[PATCH v3 6/7] rust: percpu: Add pin-hole optimizations for numerics

[Mitchell Levy]

The C implementations of `this_cpu_add`, `this_cpu_sub`, etc., are
optimized to save an instruction by avoiding having to compute
`this_cpu_ptr(&x)` for some per-CPU variable `x`. For example, rather
than

    u64 *x_ptr = this_cpu_ptr(&x);
    *x_ptr += 5;

the implementation of `this_cpu_add` is clever enough to make use of the
fact that per-CPU variables are implemented on x86 via segment
registers, and so we can use only a single instruction (where we assume
`&x` is already in `rax`)

    add gs:[rax], 5

Add this optimization via a `PerCpuNumeric` type to enable code-reuse
between `DynamicPerCpu` and `StaticPerCpu`.

Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>
---
 rust/kernel/percpu.rs         |   1 +
 rust/kernel/percpu/dynamic.rs |   2 +-
 rust/kernel/percpu/numeric.rs | 128 ++++++++++++++++++++++++++++++++++++++++++
 samples/rust/rust_percpu.rs   |  36 ++++++++++++
 4 files changed, 166 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/percpu.rs b/rust/kernel/percpu.rs
index c68c7520b67f..c693d16518d2 100644
--- a/rust/kernel/percpu.rs
+++ b/rust/kernel/percpu.rs
@@ -4,6 +4,7 @@
 
 pub mod cpu_guard;
 mod dynamic;
+pub mod numeric;
 mod static_;
 
 #[doc(inline)]
diff --git a/rust/kernel/percpu/dynamic.rs b/rust/kernel/percpu/dynamic.rs
index 64f04cef3705..aad08e4b4251 100644
--- a/rust/kernel/percpu/dynamic.rs
+++ b/rust/kernel/percpu/dynamic.rs
@@ -7,7 +7,7 @@
 
 /// Represents a dynamic allocation of a per-CPU variable via alloc_percpu. Calls free_percpu when
 /// dropped.
-pub struct PerCpuAllocation<T>(PerCpuPtr<T>);
+pub struct PerCpuAllocation<T>(pub(super) PerCpuPtr<T>);
 
 impl<T: Zeroable> PerCpuAllocation<T> {
     /// Dynamically allocates a space in the per-CPU area suitably sized and aligned to hold a `T`,
diff --git a/rust/kernel/percpu/numeric.rs b/rust/kernel/percpu/numeric.rs
new file mode 100644
index 000000000000..4de93f653f0e
--- /dev/null
+++ b/rust/kernel/percpu/numeric.rs
@@ -0,0 +1,128 @@
+// SPDX-License-Identifier: GPL-2.0
+//! Pin-hole optimizations for PerCpu<T> where T is a numeric type.
+
+use super::*;
+use core::arch::asm;
+
+/// Represents a per-CPU variable that can be manipulated with machine-intrinsic numeric
+/// operations.
+pub struct PerCpuNumeric<'a, T> {
+    // INVARIANT: `ptr.0` is a valid offset into the per-CPU area and is initialized on all CPUs
+    // (since we don't have a CPU guard, we have to be pessimistic and assume we could be on any
+    // CPU).
+    ptr: &'a PerCpuPtr<T>,
+}
+
+macro_rules! impl_ops {
+    ($ty:ty, $reg:tt) => {
+        impl DynamicPerCpu<$ty> {
+            /// Returns a `PerCpuNumeric` that can be used to manipulate the underlying per-CPU variable.
+            pub fn num(&mut self) -> PerCpuNumeric<'_, $ty> {
+                // The invariant is satisfied because `DynamicPerCpu`'s invariant guarantees that
+                // this pointer is valid and initialized on all CPUs.
+                PerCpuNumeric { ptr: &self.alloc.0 }
+            }
+        }
+        impl StaticPerCpu<$ty> {
+            /// Returns a `PerCpuNumeric` that can be used to manipulate the underlying per-CPU variable.
+            pub fn num(&mut self) -> PerCpuNumeric<'_, $ty> {
+                // The invariant is satisfied because `StaticPerCpu`'s invariant guarantees that
+                // this pointer is valid and initialized on all CPUs.
+                PerCpuNumeric { ptr: &self.0 }
+            }
+        }
+
+        impl PerCpuNumeric<'_, $ty> {
+            /// Adds `rhs` to the per-CPU variable.
+            pub fn add(&mut self, rhs: $ty) {
+                // SAFETY: `self.ptr.0` is a valid offset into the per-CPU area (i.e., valid as a
+                // pointer relative to the `gs` segment register) by the invariants of this type.
+                unsafe {
+                    asm!(
+                        concat!("add gs:[{off}], {val:", $reg, "}"),
+                        off = in(reg) self.ptr.0.cast::<*mut $ty>(),
+                        val = in(reg) rhs,
+                    );
+                }
+            }
+        }
+        impl PerCpuNumeric<'_, $ty> {
+            /// Subtracts `rhs` from the per-CPU variable.
+            pub fn sub(&mut self, rhs: $ty) {
+                // SAFETY: `self.ptr.0` is a valid offset into the per-CPU area (i.e., valid as a
+                // pointer relative to the `gs` segment register) by the invariants of this type.
+                unsafe {
+                    asm!(
+                        concat!("sub gs:[{off}], {val:", $reg, "}"),
+                        off = in(reg) self.ptr.0.cast::<*mut $ty>(),
+                        val = in(reg) rhs,
+                    );
+                }
+            }
+        }
+    };
+}
+
+macro_rules! impl_ops_byte {
+    ($ty:ty) => {
+        impl DynamicPerCpu<$ty> {
+            /// Returns a `PerCpuNumeric` that can be used to manipulate the underlying per-CPU
+            /// variable.
+            pub fn num(&mut self) -> PerCpuNumeric<'_, $ty> {
+                // The invariant is satisfied because `DynamicPerCpu`'s invariant guarantees that
+                // this pointer is valid and initialized on all CPUs.
+                PerCpuNumeric { ptr: &self.alloc.0 }
+            }
+        }
+        impl StaticPerCpu<$ty> {
+            /// Returns a `PerCpuNumeric` that can be used to manipulate the underlying per-CPU
+            /// variable.
+            pub fn num(&mut self) -> PerCpuNumeric<'_, $ty> {
+                // The invariant is satisfied because `DynamicPerCpu`'s invariant guarantees that
+                // this pointer is valid and initialized on all CPUs.
+                PerCpuNumeric { ptr: &self.0 }
+            }
+        }
+
+        impl PerCpuNumeric<'_, $ty> {
+            /// Adds `rhs` to the per-CPU variable.
+            pub fn add(&mut self, rhs: $ty) {
+                // SAFETY: `self.ptr.0` is a valid offset into the per-CPU area (i.e., valid as a
+                // pointer relative to the `gs` segment register) by the invariants of this type.
+                unsafe {
+                    asm!(
+                        concat!("add gs:[{off}], {val}"),
+                        off = in(reg) self.ptr.0.cast::<*mut $ty>(),
+                        val = in(reg_byte) rhs,
+                    );
+                }
+            }
+        }
+        impl PerCpuNumeric<'_, $ty> {
+            /// Subtracts `rhs` from the per-CPU variable.
+            pub fn sub(&mut self, rhs: $ty) {
+                // SAFETY: `self.ptr.0` is a valid offset into the per-CPU area (i.e., valid as a
+                // pointer relative to the `gs` segment register) by the invariants of this type.
+                unsafe {
+                    asm!(
+                        concat!("sub gs:[{off}], {val}"),
+                        off = in(reg) self.ptr.0.cast::<*mut $ty>(),
+                        val = in(reg_byte) rhs,
+                    );
+                }
+            }
+        }
+    };
+}
+
+impl_ops_byte!(i8);
+impl_ops!(i16, "x");
+impl_ops!(i32, "e");
+impl_ops!(i64, "r");
+impl_ops!(isize, "r");
+
+impl_ops_byte!(u8);
+impl_ops!(u16, "x");
+impl_ops!(u32, "e");
+impl_ops!(u64, "r");
+impl_ops!(usize, "r");
diff --git a/samples/rust/rust_percpu.rs b/samples/rust/rust_percpu.rs
index 06b322019134..e3a46a053b8d 100644
--- a/samples/rust/rust_percpu.rs
+++ b/samples/rust/rust_percpu.rs
@@ -27,6 +27,26 @@
 define_per_cpu!(UPERCPU: u64 = 0);
 define_per_cpu!(CHECKED: RefCell<u64> = RefCell::new(0));
 
+macro_rules! make_optimization_test {
+    ($ty:ty) => {
+        let mut test: DynamicPerCpu<$ty> = DynamicPerCpu::new_zero(GFP_KERNEL).unwrap();
+        {
+            let _ = CpuGuard::new();
+            // SAFETY: No other usage of `test`
+            unsafe { test.get_mut(CpuGuard::new()) }.with(|val: &mut $ty| *val = 10);
+            test.num().add(1);
+            // SAFETY: No other usage of `test`
+            unsafe { test.get_mut(CpuGuard::new()) }.with(|val: &mut $ty| assert_eq!(*val, 11));
+            test.num().add(10);
+            // SAFETY: No other usage of `test`
+            unsafe { test.get_mut(CpuGuard::new()) }.with(|val: &mut $ty| assert_eq!(*val, 21));
+            test.num().sub(5);
+            // SAFETY: No other usage of `test`
+            unsafe { test.get_mut(CpuGuard::new()) }.with(|val: &mut $ty| assert_eq!(*val, 16));
+        }
+    };
+}
+
 impl kernel::Module for PerCpuMod {
     fn init(_module: &'static ThisModule) -> Result<Self, Error> {
         pr_info!("rust percpu test start\n");
@@ -198,6 +218,22 @@ fn init(_module: &'static ThisModule) -> Result<Self, Error> {
 
         pr_info!("rust dynamic percpu test done\n");
 
+        pr_info!("rust numeric optimizations test start\n");
+
+        make_optimization_test!(u8);
+        make_optimization_test!(u16);
+        make_optimization_test!(u32);
+        make_optimization_test!(u64);
+        make_optimization_test!(usize);
+
+        make_optimization_test!(i8);
+        make_optimization_test!(i16);
+        make_optimization_test!(i32);
+        make_optimization_test!(i64);
+        make_optimization_test!(isize);
+
+        pr_info!("rust numeric optimizations test done\n");
+
         // Return Err to unload the module
         Result::Err(EINVAL)
     }

-- 
2.34.1

[PATCH v3 7/7] rust: percpu: cache per-CPU pointers in the dynamic case

[Mitchell Levy]

Currently, the creation of a `PerCpuNumeric` requires a memory read via
the `Arc` managing the dynamic allocation. While the compiler might be
clever enough to consolidate these reads in some cases, the read must
happen *somewhere*, which, when we're concerning ourselves with
individual instructions, is a very high burden.

Instead, cache the `PerCpuPointer` inside the `DynamicPerCpu` structure;
then, the `Arc` is used solely to manage the allocation.

Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>
---
 rust/kernel/percpu/dynamic.rs | 8 ++++++--
 rust/kernel/percpu/numeric.rs | 4 ++--
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/rust/kernel/percpu/dynamic.rs b/rust/kernel/percpu/dynamic.rs
index aad08e4b4251..8683e94bcd9f 100644
--- a/rust/kernel/percpu/dynamic.rs
+++ b/rust/kernel/percpu/dynamic.rs
@@ -58,7 +58,10 @@ fn drop(&mut self) {
 pub struct DynamicPerCpu<T> {
     // INVARIANT: The memory location in each CPU's per-CPU area pointed at by `alloc.0` has been
     // initialized.
+    // INVARIANT: `ptr` is the per-CPU pointer managed by `alloc`, which does not change for the
+    // lifetime of `self`.
     pub(super) alloc: Arc<PerCpuAllocation<T>>,
+    pub(super) ptr: PerCpuPtr<T>,
 }
 
 impl<T: Zeroable> DynamicPerCpu<T> {
@@ -70,9 +73,10 @@ impl<T: Zeroable> DynamicPerCpu<T> {
     pub fn new_zero(flags: Flags) -> Option<Self> {
         let alloc: PerCpuAllocation<T> = PerCpuAllocation::new_zero()?;
 
+        let ptr = alloc.0;
         let arc = Arc::new(alloc, flags).ok()?;
 
-        Some(Self { alloc: arc })
+        Some(Self { alloc: arc, ptr })
     }
 }
 
@@ -102,7 +106,7 @@ pub fn new_with(val: T, flags: Flags) -> Option<Self> {
 
         let arc = Arc::new(alloc, flags).ok()?;
 
-        Some(Self { alloc: arc })
+        Some(Self { alloc: arc, ptr })
     }
 }
 
diff --git a/rust/kernel/percpu/numeric.rs b/rust/kernel/percpu/numeric.rs
index 4de93f653f0e..3412c2de85fd 100644
--- a/rust/kernel/percpu/numeric.rs
+++ b/rust/kernel/percpu/numeric.rs
@@ -20,7 +20,7 @@ impl DynamicPerCpu<$ty> {
             pub fn num(&mut self) -> PerCpuNumeric<'_, $ty> {
                 // The invariant is satisfied because `DynamicPerCpu`'s invariant guarantees that
                 // this pointer is valid and initialized on all CPUs.
-                PerCpuNumeric { ptr: &self.alloc.0 }
+                PerCpuNumeric { ptr: &self.ptr }
             }
         }
         impl StaticPerCpu<$ty> {
@@ -71,7 +71,7 @@ impl DynamicPerCpu<$ty> {
             pub fn num(&mut self) -> PerCpuNumeric<'_, $ty> {
                 // The invariant is satisfied because `DynamicPerCpu`'s invariant guarantees that
                 // this pointer is valid and initialized on all CPUs.
-                PerCpuNumeric { ptr: &self.alloc.0 }
+                PerCpuNumeric { ptr: &self.ptr }
             }
         }
         impl StaticPerCpu<$ty> {

-- 
2.34.1

Re: [PATCH v3 3/7] rust: cpumask: Add a `Cpumask` iterator

[Viresh Kumar]

On 28-08-25, 12:00, Mitchell Levy wrote:
> Add an iterator for `Cpumask` making use of C's `cpumask_next`.
> 
> Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>
> ---
>  rust/helpers/cpumask.c |  5 +++++
>  rust/kernel/cpumask.rs | 48 +++++++++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 52 insertions(+), 1 deletion(-)

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>

-- 
viresh

Re: [PATCH v3 4/7] rust: cpumask: Add getters for globally defined cpumasks

[Viresh Kumar]

On 28-08-25, 12:00, Mitchell Levy wrote:
> Add getters for the global cpumasks documented in
> `include/linux/cpumask.h`, specifically:
> - cpu_possible_mask
> - cpu_online_mask
> - cpu_enabled_mask
> - cpu_present_mask
> - cpu_active_mask
> 
> Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>
> ---
>  rust/kernel/cpumask.rs | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 46 insertions(+)

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>

-- 
viresh