From: Hui Zhu <zhuhui@kylinos.cn>

Add a test module to verify memory alignment guarantees for Rust kernel
allocators.
The tests cover `Kmalloc`, `Vmalloc` and `KVmalloc` allocators
with both standard and large page-aligned allocations.

Key features of the tests:
1. Creates alignment-constrained types:
   - 128-byte aligned `Blob`
   - 8192-byte (4-page) aligned `LargeAlignBlob`
2. Validates allocators using `TestAlign` helper which:
   - Checks address alignment masks
   - Supports uninitialized allocations
3. Tests all three allocators with both alignment requirements:
   - Kmalloc with 128B and 8192B
   - Vmalloc with 128B and 8192B
   - KVmalloc with 128B and 8192B

Co-developed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
---
 rust/kernel/alloc/allocator.rs | 56 ++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)

diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
index 63f271624428..1f173038cec9 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -184,3 +184,59 @@ unsafe fn realloc(
         unsafe { ReallocFunc::KVREALLOC.call(ptr, layout, old_layout, flags, nid) }
     }
 }
+
+#[macros::kunit_tests(rust_allocator_kunit)]
+mod tests {
+    use super::*;
+    use core::mem::MaybeUninit;
+    use kernel::prelude::*;
+
+    #[test]
+    fn test_alignment() -> Result<()> {
+        const TEST_SIZE: usize = 1024;
+        const TEST_LARGE_ALIGN_SIZE: usize = kernel::page::PAGE_SIZE * 4;
+
+        // These two structs are used to test allocating aligned memory.
+        // they don't need to be accessed, so they're marked as dead_code.
+        #[expect(dead_code)]
+        #[repr(align(128))]
+        struct Blob([u8; TEST_SIZE]);
+        #[expect(dead_code)]
+        #[repr(align(8192))]
+        struct LargeAlignBlob([u8; TEST_LARGE_ALIGN_SIZE]);
+
+        struct TestAlign<T, A: Allocator>(Box<MaybeUninit<T>, A>);
+        impl<T, A: Allocator> TestAlign<T, A> {
+            fn new() -> Result<Self> {
+                Ok(Self(Box::<_, A>::new_uninit(GFP_KERNEL)?))
+            }
+
+            fn alignment_valid(&self, align: usize) -> bool {
+                assert!(align.is_power_of_two());
+
+                let addr = self.0.as_ptr() as usize;
+                addr & (align - 1) == 0
+            }
+        }
+
+        let ta = TestAlign::<Blob, Kmalloc>::new()?;
+        assert!(ta.alignment_valid(128));
+
+        let ta = TestAlign::<LargeAlignBlob, Kmalloc>::new()?;
+        assert!(ta.alignment_valid(8192));
+
+        let ta = TestAlign::<Blob, Vmalloc>::new()?;
+        assert!(ta.alignment_valid(128));
+
+        let ta = TestAlign::<LargeAlignBlob, Vmalloc>::new()?;
+        assert!(ta.alignment_valid(8192));
+
+        let ta = TestAlign::<Blob, KVmalloc>::new()?;
+        assert!(ta.alignment_valid(128));
+
+        let ta = TestAlign::<LargeAlignBlob, KVmalloc>::new()?;
+        assert!(ta.alignment_valid(8192));
+
+        Ok(())
+    }
+}
-- 
2.43.0

On Wed, Jul 30, 2025 at 5:37 AM Hui Zhu <hui.zhu@linux.dev> wrote:
>
> +#[macros::kunit_tests(rust_allocator_kunit)]

Is there any reason for the `_kunit` suffix? If not, then we should
avoid suffixing `_kunit` to every suite name.

I see we already have `rust_kernel_kunit`, but that one is because it
is the KUnit file itself.

There is also `rust_kvec_kunit`, but we should clean that one up.

> +    fn test_alignment() -> Result<()> {

`-> Result` since the prelude is available.

> +            fn alignment_valid(&self, align: usize) -> bool {

We typically prefix these with `is_`.

I would also call it `is_aligned_to`, to match the upstream Rust one,
which we could perhaps use if it becomes stable.

Cheers,
Miguel

2025年7月30日 17:16, "Miguel Ojeda" <miguel.ojeda.sandonis@gmail.com mailto:miguel.ojeda.sandonis@gmail.com?to=%22Miguel%20Ojeda%22%20%3Cmiguel.ojeda.sandonis%40gmail.com%3E > 写到:


> 
> On Wed, Jul 30, 2025 at 5:37 AM Hui Zhu <hui.zhu@linux.dev> wrote:
> 
> > 
> > +#[macros::kunit_tests(rust_allocator_kunit)]
> > 
> Is there any reason for the `_kunit` suffix? If not, then we should
> avoid suffixing `_kunit` to every suite name.
> 
> I see we already have `rust_kernel_kunit`, but that one is because it
> is the KUnit file itself.
> 
> There is also `rust_kvec_kunit`, but we should clean that one up.
> 
> > 
> > + fn test_alignment() -> Result<()> {
> > 
> `-> Result` since the prelude is available.
> 
> > 
> > + fn alignment_valid(&self, align: usize) -> bool {
> > 
> We typically prefix these with `is_`.
> 
> I would also call it `is_aligned_to`, to match the upstream Rust one,
> which we could perhaps use if it becomes stable.
> 

Hi Miguel,

I sent the v7 version according to your comments.

Thanks,
Hui

> Cheers,
> Miguel
>

On Wed, Jul 30, 2025 at 11:35:21AM +0800, Hui Zhu wrote:
> From: Hui Zhu <zhuhui@kylinos.cn>
> 
> Add a test module to verify memory alignment guarantees for Rust kernel
> allocators.
> The tests cover `Kmalloc`, `Vmalloc` and `KVmalloc` allocators
> with both standard and large page-aligned allocations.
> 
> Key features of the tests:
> 1. Creates alignment-constrained types:
>    - 128-byte aligned `Blob`
>    - 8192-byte (4-page) aligned `LargeAlignBlob`
> 2. Validates allocators using `TestAlign` helper which:
>    - Checks address alignment masks
>    - Supports uninitialized allocations
> 3. Tests all three allocators with both alignment requirements:
>    - Kmalloc with 128B and 8192B
>    - Vmalloc with 128B and 8192B
>    - KVmalloc with 128B and 8192B
> 
> Co-developed-by: Geliang Tang <geliang@kernel.org>
> Signed-off-by: Geliang Tang <geliang@kernel.org>
> Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>

Reviewed-by: Alice Ryhl <aliceryhl@google.com>