[PATCH v3 07/25] rust: alloc: implement `KVmalloc` allocator

Danilo Krummrich
2024-08-01T00:07:30Z

Implement `Allocator` for `KVmalloc`, an `Allocator` that tries to
allocate memory wth `kmalloc` first and, on failure, falls back to
`vmalloc`.

All memory allocations made with `KVmalloc` end up in
`kvrealloc_noprof()`; all frees in `kvfree()`.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
rust/helpers.c | 7 +++++++
rust/kernel/alloc/allocator.rs | 24 ++++++++++++++++++++++++
rust/kernel/alloc/allocator_test.rs | 1 +
3 files changed, 32 insertions(+)

diff --git a/rust/helpers.c b/rust/helpers.c
index 4c628986f0c9..4ad7dc347523 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -208,6 +208,13 @@ rust_helper_vrealloc(const void *p, size_t size, gfp_t flags)
}
EXPORT_SYMBOL_GPL(rust_helper_vrealloc);

+void * __must_check __realloc_size(2)
+rust_helper_kvrealloc(const void *p, size_t size, gfp_t flags)
+{
+ return kvrealloc(p, size, flags);
+}
+EXPORT_SYMBOL_GPL(rust_helper_kvrealloc);
+
/*
* `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 e9a3d0694f41..1e53f149db96 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -22,6 +22,12 @@
/// contiguous kernel virtual space.
pub struct Vmalloc;

+/// The kvmalloc kernel allocator.
+///
+/// Attempt to allocate physically contiguous memory, but upon failure, fall back to non-contiguous
+/// (vmalloc) allocation.
+pub struct KVmalloc;
+
/// 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.
@@ -68,6 +74,10 @@ fn vrealloc() -> Self {
Self(bindings::vrealloc)
}

+ fn kvrealloc() -> Self {
+ Self(bindings::kvrealloc)
+ }
+
// SAFETY: `call` has the exact same safety requirements as `Allocator::realloc`.
unsafe fn call(
&self,
@@ -160,6 +170,20 @@ unsafe fn realloc(
}
}

+unsafe impl Allocator for KVmalloc {
+ unsafe fn realloc(
+ ptr: Option<NonNull<u8>>,
+ layout: Layout,
+ flags: Flags,
+ ) -> Result<NonNull<[u8]>, AllocError> {
+ let realloc = ReallocFunc::kvrealloc();
+
+ // 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 e7bf2982f68f..1b2642c547ec 100644
--- a/rust/kernel/alloc/allocator_test.rs
+++ b/rust/kernel/alloc/allocator_test.rs
@@ -8,6 +8,7 @@

pub struct Kmalloc;
pub type Vmalloc = Kmalloc;
+pub type KVmalloc = Kmalloc;

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