Add a static check to see if we properly align our struct hvt_ring on 2 cache-lines

Co-authored-by: Reynir Björnsson <reynir@reynir.dk>

Author: dinosaure

include/hvt_ring.h

@@ -27,6 +27,7 @@
 #ifndef HVT_RING_H
 #define HVT_RING_H
 
+#include <stddef.h>
 #include <stdint.h>
 
 #define HVT_RING_SIZE 1024
@@ -94,6 +95,16 @@ struct hvt_ring {
     struct hvt_ring_commit commits[HVT_RING_SIZE];
 };
 
+/*
+ * Verify that guest-written and host-written fields live on distinct cache
+ * lines (64 bytes each), and that the data arrays start after exactly 2
+ * cache lines of index/control fields.
+ */
+_Static_assert(offsetof(struct hvt_ring, ent_head) == 64,
+    "ent_head must start at cache line 1 (offset 64)");
+_Static_assert(offsetof(struct hvt_ring, entries) == 128,
+    "entries[] must start after 2 cache lines (offset 128)");
+
 /*
  * Memory barriers.
  *