linux-kernel - [PATCH v4 3/4] rust: support large alignments in allocations

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Message-Id: <20250626083642.3596388-1-vitaly.wool@konsulko.se>
Date: Thu, 26 Jun 2025 10:36:42 +0200
From: Vitaly Wool <vitaly.wool@...sulko.se>
To: linux-mm@...ck.org
Cc: akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org,
	Uladzislau Rezki <urezki@...il.com>,
	Danilo Krummrich <dakr@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>,
	rust-for-linux@...r.kernel.org,
	Vitaly Wool <vitaly.wool@...sulko.se>
Subject: [PATCH v4 3/4] rust: support large alignments in allocations

Add support for large (> PAGE_SIZE) alignments in Rust allocators
(Kmalloc support for large alignments is limited to the requested
size, which is a reasonable limitation anyway).

Signed-off-by: Vitaly Wool <vitaly.wool@...sulko.se>
---
 rust/helpers/slab.c            |  4 ++--
 rust/helpers/vmalloc.c         |  4 ++--
 rust/kernel/alloc/allocator.rs | 16 ++--------------
 3 files changed, 6 insertions(+), 18 deletions(-)

diff --git a/rust/helpers/slab.c b/rust/helpers/slab.c
index a842bfbddcba..5e9e8dd2bba0 100644
--- a/rust/helpers/slab.c
+++ b/rust/helpers/slab.c
@@ -3,13 +3,13 @@
 #include <linux/slab.h>
 
 void * __must_check __realloc_size(2)
-rust_helper_krealloc(const void *objp, size_t new_size, gfp_t flags)
+rust_helper_krealloc(const void *objp, size_t new_size, unsigned long align, gfp_t flags)
 {
 	return krealloc(objp, new_size, flags);
 }
 
 void * __must_check __realloc_size(2)
-rust_helper_kvrealloc(const void *p, size_t size, gfp_t flags)
+rust_helper_kvrealloc(const void *p, size_t size, unsigned long align, gfp_t flags)
 {
 	return kvrealloc(p, size, flags);
 }
diff --git a/rust/helpers/vmalloc.c b/rust/helpers/vmalloc.c
index 80d34501bbc0..4618c0b79283 100644
--- a/rust/helpers/vmalloc.c
+++ b/rust/helpers/vmalloc.c
@@ -3,7 +3,7 @@
 #include <linux/vmalloc.h>
 
 void * __must_check __realloc_size(2)
-rust_helper_vrealloc(const void *p, size_t size, gfp_t flags)
+rust_helper_vrealloc(const void *p, size_t size, unsigned long align, gfp_t flags)
 {
-	return vrealloc(p, size, flags);
+	return vrealloc_node(p, size, align, flags, NUMA_NO_NODE);
 }
diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
index aa2dfa9dca4c..a0d78c497974 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -58,7 +58,7 @@ fn aligned_size(new_layout: Layout) -> usize {
 ///
 /// One of the following: `krealloc`, `vrealloc`, `kvrealloc`.
 struct ReallocFunc(
-    unsafe extern "C" fn(*const crate::ffi::c_void, usize, u32) -> *mut crate::ffi::c_void,
+    unsafe extern "C" fn(*const crate::ffi::c_void, usize, usize, u32) -> *mut crate::ffi::c_void,
 );
 
 impl ReallocFunc {
@@ -110,7 +110,7 @@ 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).cast()
+            self.0(ptr.cast(), size, layout.align(), flags.0).cast()
         };
 
         let ptr = if size == 0 {
@@ -152,12 +152,6 @@ unsafe fn realloc(
         old_layout: Layout,
         flags: Flags,
     ) -> 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) }
@@ -176,12 +170,6 @@ unsafe fn realloc(
         old_layout: Layout,
         flags: Flags,
     ) -> 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) }
-- 
2.39.2