[PATCH v3 06/25] rust: alloc: implement `Vmalloc` allocator

Danilo Krummrich
2024-08-01T00:07:25Z

Implement `Allocator` for `Vmalloc`, the kernel's virtually contiguous
allocator, typically used for larger objects, (much) larger than page
size.

All memory allocations made with `Vmalloc` end up in `vrealloc()`.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
rust/helpers.c | 8 ++++++++
rust/kernel/alloc/allocator.rs | 24 ++++++++++++++++++++++++
rust/kernel/alloc/allocator_test.rs | 1 +
3 files changed, 33 insertions(+)

diff --git a/rust/helpers.c b/rust/helpers.c
index 92d3c03ae1bd..4c628986f0c9 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -33,6 +33,7 @@
#include <linux/sched/signal.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
+#include <linux/vmalloc.h>
#include <linux/wait.h>
#include <linux/workqueue.h>

@@ -200,6 +201,13 @@ rust_helper_krealloc(const void *objp, size_t new_size, gfp_t flags)
}
EXPORT_SYMBOL_GPL(rust_helper_krealloc);

+void * __must_check __realloc_size(2)
+rust_helper_vrealloc(const void *p, size_t size, gfp_t flags)
+{
+ return vrealloc(p, size, flags);
+}
+EXPORT_SYMBOL_GPL(rust_helper_vrealloc);
+
/*
* `bindgen` binds the C `size_t` type as the Rust `usize` type, so we can
* use it in contexts where Rust expects a `usize` like slice (array) indices.
diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
index 397ae5bcc043..e9a3d0694f41 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -16,6 +16,12 @@
/// `bindings::krealloc`.
pub struct Kmalloc;

+/// The virtually contiguous kernel allocator.
+///
+/// The vmalloc allocator allocates pages from the page level allocator and maps them into the
+/// contiguous kernel virtual space.
+pub struct Vmalloc;
+
/// Returns a proper size to alloc a new object aligned to `new_layout`'s alignment.
fn aligned_size(new_layout: Layout) -> usize {
// Customized layouts from `Layout::from_size_align()` can have size < align, so pad first.
@@ -58,6 +64,10 @@ fn krealloc() -> Self {
Self(bindings::krealloc)
}

+ fn vrealloc() -> Self {
+ Self(bindings::vrealloc)
+ }
+
// SAFETY: `call` has the exact same safety requirements as `Allocator::realloc`.
unsafe fn call(
&self,
@@ -136,6 +146,20 @@ unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
}
}

+unsafe impl Allocator for Vmalloc {
+ unsafe fn realloc(
+ ptr: Option<NonNull<u8>>,
+ layout: Layout,
+ flags: Flags,
+ ) -> Result<NonNull<[u8]>, AllocError> {
+ let realloc = ReallocFunc::vrealloc();
+
+ // SAFETY: If not `None`, `ptr` is guaranteed to point to valid memory, which was previously
+ // allocated with this `Allocator`.
+ unsafe { realloc.call(ptr, layout, flags) }
+ }
+}
+
#[global_allocator]
static ALLOCATOR: Kmalloc = Kmalloc;

diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs
index 4785efc474a7..e7bf2982f68f 100644
--- a/rust/kernel/alloc/allocator_test.rs
+++ b/rust/kernel/alloc/allocator_test.rs
@@ -7,6 +7,7 @@
use core::ptr::NonNull;

pub struct Kmalloc;
+pub type Vmalloc = Kmalloc;

unsafe impl Allocator for Kmalloc {
unsafe fn realloc(
--
2.45.2