Add support for large (> PAGE_SIZE) alignments in Rust allocators.
All the preparations on the C side are already done, we just need
to add bindings for <alloc>_node_align() functions and start
using those.

Signed-off-by: Vitaly Wool <vitaly.wool@konsulko.se>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Acked-by: Alice Ryhl <aliceryhl@google.com>
---
 rust/helpers/slab.c                 | 10 ++++++----
 rust/helpers/vmalloc.c              |  5 +++--
 rust/kernel/alloc/allocator.rs      | 30 +++++++++--------------------
 rust/kernel/alloc/allocator_test.rs |  1 +
 4 files changed, 19 insertions(+), 27 deletions(-)

diff --git a/rust/helpers/slab.c b/rust/helpers/slab.c
index 8472370a4338..7fac958907b0 100644
--- a/rust/helpers/slab.c
+++ b/rust/helpers/slab.c
@@ -3,13 +3,15 @@
 #include <linux/slab.h>
 
 void * __must_check __realloc_size(2)
-rust_helper_krealloc_node(const void *objp, size_t new_size, gfp_t flags, int node)
+rust_helper_krealloc_node_align(const void *objp, size_t new_size, unsigned long align,
+				gfp_t flags, int node)
 {
-	return krealloc_node(objp, new_size, flags, node);
+	return krealloc_node_align(objp, new_size, align, flags, node);
 }
 
 void * __must_check __realloc_size(2)
-rust_helper_kvrealloc_node(const void *p, size_t size, gfp_t flags, int node)
+rust_helper_kvrealloc_node_align(const void *p, size_t size, unsigned long align,
+				 gfp_t flags, int node)
 {
-	return kvrealloc_node(p, size, flags, node);
+	return kvrealloc_node_align(p, size, align, flags, node);
 }
diff --git a/rust/helpers/vmalloc.c b/rust/helpers/vmalloc.c
index 62d30db9a1a6..7d7f7336b3d2 100644
--- a/rust/helpers/vmalloc.c
+++ b/rust/helpers/vmalloc.c
@@ -3,7 +3,8 @@
 #include <linux/vmalloc.h>
 
 void * __must_check __realloc_size(2)
-rust_helper_vrealloc_node(const void *p, size_t size, gfp_t flags, int node)
+rust_helper_vrealloc_node_align(const void *p, size_t size, unsigned long align,
+				gfp_t flags, int node)
 {
-	return vrealloc_node(p, size, flags, node);
+	return vrealloc_node_align(p, size, align, flags, node);
 }
diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
index 8af7e04e3cc6..63f271624428 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -15,7 +15,6 @@
 
 use crate::alloc::{AllocError, Allocator, NumaNode};
 use crate::bindings;
-use crate::pr_warn;
 
 /// The contiguous kernel allocator.
 ///
@@ -56,25 +55,26 @@ fn aligned_size(new_layout: Layout) -> usize {
 
 /// # Invariants
 ///
-/// One of the following: `krealloc_node`, `vrealloc_node`, `kvrealloc_node`.
+/// One of the following: `krealloc_node_align`, `vrealloc_node_align`, `kvrealloc_node_align`.
 struct ReallocFunc(
     unsafe extern "C" fn(
         *const crate::ffi::c_void,
         usize,
+        crate::ffi::c_ulong,
         u32,
         crate::ffi::c_int,
     ) -> *mut crate::ffi::c_void,
 );
 
 impl ReallocFunc {
-    // INVARIANT: `krealloc_node` satisfies the type invariants.
-    const KREALLOC: Self = Self(bindings::krealloc_node);
+    // INVARIANT: `krealloc_node_align` satisfies the type invariants.
+    const KREALLOC: Self = Self(bindings::krealloc_node_align);
 
-    // INVARIANT: `vrealloc_node` satisfies the type invariants.
-    const VREALLOC: Self = Self(bindings::vrealloc_node);
+    // INVARIANT: `vrealloc_node_align` satisfies the type invariants.
+    const VREALLOC: Self = Self(bindings::vrealloc_node_align);
 
-    // INVARIANT: `kvrealloc_node` satisfies the type invariants.
-    const KVREALLOC: Self = Self(bindings::kvrealloc_node);
+    // INVARIANT: `kvrealloc_node_align` satisfies the type invariants.
+    const KVREALLOC: Self = Self(bindings::kvrealloc_node_align);
 
     /// # Safety
     ///
@@ -116,7 +116,7 @@ unsafe fn call(
         // - Those functions provide the guarantees of this function.
         let raw_ptr = unsafe {
             // If `size == 0` and `ptr != NULL` the memory behind the pointer is freed.
-            self.0(ptr.cast(), size, flags.0, nid.0).cast()
+            self.0(ptr.cast(), size, layout.align(), flags.0, nid.0).cast()
         };
 
         let ptr = if size == 0 {
@@ -160,12 +160,6 @@ unsafe fn realloc(
         flags: Flags,
         nid: NumaNode,
     ) -> Result<NonNull<[u8]>, AllocError> {
-        // TODO: Support alignments larger than PAGE_SIZE.
-        if layout.align() > bindings::PAGE_SIZE {
-            pr_warn!("Vmalloc does not support alignments larger than PAGE_SIZE yet.\n");
-            return Err(AllocError);
-        }
-
         // SAFETY: If not `None`, `ptr` is guaranteed to point to valid memory, which was previously
         // allocated with this `Allocator`.
         unsafe { ReallocFunc::VREALLOC.call(ptr, layout, old_layout, flags, nid) }
@@ -185,12 +179,6 @@ unsafe fn realloc(
         flags: Flags,
         nid: NumaNode,
     ) -> Result<NonNull<[u8]>, AllocError> {
-        // TODO: Support alignments larger than PAGE_SIZE.
-        if layout.align() > bindings::PAGE_SIZE {
-            pr_warn!("KVmalloc does not support alignments larger than PAGE_SIZE yet.\n");
-            return Err(AllocError);
-        }
-
         // SAFETY: If not `None`, `ptr` is guaranteed to point to valid memory, which was previously
         // allocated with this `Allocator`.
         unsafe { ReallocFunc::KVREALLOC.call(ptr, layout, old_layout, flags, nid) }
diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs
index d19c06ef0498..17b27c6e9e37 100644
--- a/rust/kernel/alloc/allocator_test.rs
+++ b/rust/kernel/alloc/allocator_test.rs
@@ -40,6 +40,7 @@ unsafe fn realloc(
         layout: Layout,
         old_layout: Layout,
         flags: Flags,
+        nid: NumaNode,
     ) -> Result<NonNull<[u8]>, AllocError> {
         let src = match ptr {
             Some(src) => {
-- 
2.39.2

On Wed Jul 30, 2025 at 9:21 PM CEST, Vitaly Wool wrote:
> diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs
> index d19c06ef0498..17b27c6e9e37 100644
> --- a/rust/kernel/alloc/allocator_test.rs
> +++ b/rust/kernel/alloc/allocator_test.rs
> @@ -40,6 +40,7 @@ unsafe fn realloc(
>          layout: Layout,
>          old_layout: Layout,
>          flags: Flags,
> +        nid: NumaNode,
>      ) -> Result<NonNull<[u8]>, AllocError> {
>          let src = match ptr {
>              Some(src) => {

I think this hunk should be on patch 3.

Also, don't you see a warning when running the rusttest target? I think it has
to be _nid, given that the argument is unused.

> On Jul 30, 2025, at 10:18 PM, Danilo Krummrich <dakr@kernel.org> wrote:
> 
> On Wed Jul 30, 2025 at 9:21 PM CEST, Vitaly Wool wrote:
>> diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs
>> index d19c06ef0498..17b27c6e9e37 100644
>> --- a/rust/kernel/alloc/allocator_test.rs
>> +++ b/rust/kernel/alloc/allocator_test.rs
>> @@ -40,6 +40,7 @@ unsafe fn realloc(
>>         layout: Layout,
>>         old_layout: Layout,
>>         flags: Flags,
>> +        nid: NumaNode,
>>     ) -> Result<NonNull<[u8]>, AllocError> {
>>         let src = match ptr {
>>             Some(src) => {
> 
> I think this hunk should be on patch 3.
> 
> Also, don't you see a warning when running the rusttest target? I think it has
> to be _nid, given that the argument is unused.

Indeed, thanks. I’ll respin the patchset shortly.

~Vitaly