Patch "virtio_net: fix PAGE_SIZE > 64k" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

virtio_net: fix PAGE_SIZE > 64k

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
virtio_net-fix-page_size-64k.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Michael S. Tsirkin" <[email protected]>
Date: Mon, 23 Jan 2017 21:37:52 +0200
Subject: virtio_net: fix PAGE_SIZE > 64k

From: "Michael S. Tsirkin" <[email protected]>

[ Upstream commit d0fa28f00052391b5df328f502fbbdd4444938b7 ]

I don't have any guests with PAGE_SIZE > 64k but the code seems to be clearly broken in that case
as PAGE_SIZE / MERGEABLE_BUFFER_ALIGN will need
more than 8 bit and so the code in mergeable_ctx_to_buf_address does not give us the actual true size.

---
 drivers/net/virtio_net.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

@@ -47,8 +47,16 @@ module_param(gso, bool, 0444);
  */
 DECLARE_EWMA(pkt_len, 1, 64)
 
+/* With mergeable buffers we align buffer address and use the low bits to
+ * encode its true size. Buffer size is up to 1 page so we need to align to
+ * square root of page size to ensure we reserve enough bits to encode the true
+ * size.
+ */
+#define MERGEABLE_BUFFER_MIN_ALIGN_SHIFT ((PAGE_SHIFT + 1) / 2)
+
 /* Minimum alignment for mergeable packet buffers. */
-#define MERGEABLE_BUFFER_ALIGN max(L1_CACHE_BYTES, 256)
+#define MERGEABLE_BUFFER_ALIGN max(L1_CACHE_BYTES, \
+				   1 << MERGEABLE_BUFFER_MIN_ALIGN_SHIFT)
 
 #define VIRTNET_DRIVER_VERSION "1.0.0"
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/virtio_console-fix-a-crash-in-config_work_handler.patch queue-4.4/virtio_net-fix-page_size-64k.patch