On 10/15/2016 08:53 AM, Heiher wrote:
+    if ((__hptr = lock_user(VERIFY_WRITE, __gaddr, sizeof(target_type), 0))) { 
\
+        if ((old) != atomic_cmpxchg(__hptr, (old), (new)))             \
+            __ret = -TARGET_EAGAIN;                                    \
+        unlock_user(__hptr, __gaddr, sizeof(target_type));             \


This doesn't perform an atomic operation, because lock_user and unlock_user copy data from and to the guest. The atomic operation you're doing is on memory private to the host.

You also have to handle host byte order != target byte order.

That said, we are some way toward addressing this. The patch set that Emilio pointed you at is a good start.


r~

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