Hi Bin,
On 09/23/2018 04:42 PM, Bin Meng wrote:
From: Tuomas Tynkkynen <tuomas.tynkky...@iki.fi>
This adds support for managing virtual queue/ring, the channel
for high performance I/O between host and guest.
Signed-off-by: Tuomas Tynkkynen <tuomas.tynkky...@iki.fi>
Signed-off-by: Bin Meng <bmeng...@gmail.com>
---
...
+
+/*
+ * Barriers in virtio are tricky. Since we are not in a hyperviosr/guest
+ * scenario, having these as nops is enough to work as expected.
+ */
+
+static inline void virtio_mb(void)
+{
+}
+
+static inline void virtio_rmb(void)
+{
+}
+
+static inline void virtio_wmb(void)
+{
+}
+
+static inline void virtio_store_mb(__virtio16 *p, __virtio16 v)
+{
+ WRITE_ONCE(*p, v);
+}
+
+#endif /* _LINUX_VIRTIO_RING_H */
I am not convinced it's safe to leave these barriers empty. For instance
if KVM acceleration is used, I believe U-Boot could be running on one
core concurrently with QEMU's IO thread running on a different core.
Thus we need memory barriers on both sides so that updates to the
vring are observed in the correct order.
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