Drivers: hv: balloon: account for vmbus packet header in max_pkt_size

BugLink: https://bugs.launchpad.net/bugs/1959879
[ Upstream commit 96d9d1fa5cd505078534113308ced0aa56d8da58 ]

Commit adae1e931acd ("Drivers: hv: vmbus: Copy packets sent by Hyper-V
out of the ring buffer") introduced a notion of maximum packet size in
vmbus channel and used that size to initialize a buffer holding all
incoming packet along with their vmbus packet header. hv_balloon uses
the default maximum packet size VMBUS_DEFAULT_MAX_PKT_SIZE which matches
its maximum message size, however vmbus_open expects this size to also
include vmbus packet header. This leads to 4096 bytes
dm_unballoon_request messages being truncated to 4080 bytes. When the
driver tries to read next packet it starts from a wrong read_index,
receives garbage and prints a lot of "Unhandled message: type:
<garbage>" in dmesg.

Allocate the buffer with HV_HYP_PAGE_SIZE more bytes to make room for
the header.

Fixes: adae1e931acd ("Drivers: hv: vmbus: Copy packets sent by Hyper-V out of the ring buffer")
Suggested-by: Michael Kelley (LINUX) <mikelley@microsoft.com>
Suggested-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Signed-off-by: Yanming Liu <yanminglr@gmail.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Reviewed-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Link: https://lore.kernel.org/r/20220119202052.3006981-1-yanminglr@gmail.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index ca873a3b98dbe6c81023be39f98da71565af598d..f2d05bff424530d7ba28c6ac65e2874e0cc70907 100644 (file)
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -1660,6 +1660,13 @@ static int balloon_connect_vsp(struct hv_device *dev)
        unsigned long t;
        int ret;
 
+       /*
+        * max_pkt_size should be large enough for one vmbus packet header plus
+        * our receive buffer size. Hyper-V sends messages up to
+        * HV_HYP_PAGE_SIZE bytes long on balloon channel.
+        */
+       dev->channel->max_pkt_size = HV_HYP_PAGE_SIZE * 2;
+
        ret = vmbus_open(dev->channel, dm_ring_size, dm_ring_size, NULL, 0,
                         balloon_onchannelcallback, dev);
        if (ret)