rust: sync: Add memory barriers

Memory barriers are building blocks for concurrent code, hence provide
a minimal set of them.

The compiler barrier, barrier(), is implemented in inline asm instead of
using core::sync::atomic::compiler_fence() because memory models are
different: kernel's atomics are implemented in inline asm therefore the
compiler barrier should be implemented in inline asm as well. Also it's
currently only public to the kernel crate until there's a reasonable
driver usage.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Elle Rhumsaa <elle@weathered-steel.dev>
Link: https://lore.kernel.org/all/20250719030827.61357-10-boqun.feng@gmail.com/

1 files changed, 18 insertions, 0 deletions

diff --git a/rust/helpers/barrier.c b/rust/helpers/barrier.c
new file mode 100644
index 000000000000..cdf28ce8e511
--- /dev/null
+++ b/rust/helpers/barrier.c
@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <asm/barrier.h>
+
+void rust_helper_smp_mb(void)
+{
+	smp_mb();
+}
+
+void rust_helper_smp_wmb(void)
+{
+	smp_wmb();
+}
+
+void rust_helper_smp_rmb(void)
+{
+	smp_rmb();
+}