1 files changed, 39 insertions, 4 deletions

diff --git a/include/linux/vmw_vmci_defs.h b/include/linux/vmw_vmci_defs.h
index 65ac54c61c18..1bd31a38c51e 100644
--- a/include/linux/vmw_vmci_defs.h
+++ b/include/linux/vmw_vmci_defs.h
@@ -734,6 +734,41 @@ static inline void *vmci_event_data_payload(struct vmci_event_data *ev_data)
 }
 
 /*
+ * Helper to read a value from a head or tail pointer. For X86_32, the
+ * pointer is treated as a 32bit value, since the pointer value
+ * never exceeds a 32bit value in this case. Also, doing an
+ * atomic64_read on X86_32 uniprocessor systems may be implemented
+ * as a non locked cmpxchg8b, that may end up overwriting updates done
+ * by the VMCI device to the memory location. On 32bit SMP, the lock
+ * prefix will be used, so correctness isn't an issue, but using a
+ * 64bit operation still adds unnecessary overhead.
+ */
+static inline u64 vmci_q_read_pointer(atomic64_t *var)
+{
+#if defined(CONFIG_X86_32)
+        return atomic_read((atomic_t *)var);
+#else
+        return atomic64_read(var);
+#endif
+}
+
+/*
+ * Helper to set the value of a head or tail pointer. For X86_32, the
+ * pointer is treated as a 32bit value, since the pointer value
+ * never exceeds a 32bit value in this case. On 32bit SMP, using a
+ * locked cmpxchg8b adds unnecessary overhead.
+ */
+static inline void vmci_q_set_pointer(atomic64_t *var,
+                                      u64 new_val)
+{
+#if defined(CONFIG_X86_32)
+        return atomic_set((atomic_t *)var, (u32)new_val);
+#else
+        return atomic64_set(var, new_val);
+#endif
+}
+
+/*
  * Helper to add a given offset to a head or tail pointer. Wraps the
  * value of the pointer around the max size of the queue.
  */
@@ -741,14 +776,14 @@ static inline void vmci_qp_add_pointer(atomic64_t *var,
                                        size_t add,
                                        u64 size)
 {
-        u64 new_val = atomic64_read(var);
+        u64 new_val = vmci_q_read_pointer(var);
 
         if (new_val >= size - add)
                 new_val -= size;
 
         new_val += add;
 
-        atomic64_set(var, new_val);
+        vmci_q_set_pointer(var, new_val);
 }
 
 /*
@@ -758,7 +793,7 @@ static inline u64
 vmci_q_header_producer_tail(const struct vmci_queue_header *q_header)
 {
         struct vmci_queue_header *qh = (struct vmci_queue_header *)q_header;
-        return atomic64_read(&qh->producer_tail);
+        return vmci_q_read_pointer(&qh->producer_tail);
 }
 
 /*
@@ -768,7 +803,7 @@ static inline u64
 vmci_q_header_consumer_head(const struct vmci_queue_header *q_header)
 {
         struct vmci_queue_header *qh = (struct vmci_queue_header *)q_header;
-        return atomic64_read(&qh->consumer_head);
+        return vmci_q_read_pointer(&qh->consumer_head);
 }
 
 /*