diff --git a/share/man/man9/atomic.9 b/share/man/man9/atomic.9
--- a/share/man/man9/atomic.9
+++ b/share/man/man9/atomic.9
@@ -235,6 +235,15 @@
 However, they will not prevent the compiler or processor from moving loads
 or stores into the critical section, which does not violate the semantics of
 a mutex.
+.Ss Architecture-dependent caveats for compare-and-swap
+The
+.Fn atomic_[f]cmpset_<type>
+operations, specifically the ones without explicitly specified memory
+ordering variants, are defined as relaxed.
+However, the implementation on the x86
+architectures provides sequentially consistent semantics.
+On the arm64/aarch64 architecture, the operation provides acquire
+semantic for load and release semantic for store accesses.
 .Ss Thread Fence Operations
 Alternatively, a programmer can use atomic thread fence operations to
 constrain the reordering of accesses.