When the VM resumes, the host re-sends the offers. We should not add the
offers to the global vmbus_connection.chn_list again.

This patch assumes the RELIDs of the channels don't change across
hibernation. Actually this is not always true, especially in the case of
NIC SR-IOV the VF vmbus device's RELID sometimes can change. A later patch
will address this issue by mapping the new offers to the old channels and
fixing up the old channels, if necessary.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
---
 drivers/hv/channel_mgmt.c | 29 ++++++++++++++++++++++++++++-
 drivers/hv/connection.c   | 27 +++++++++++++++++++++++++++
 drivers/hv/hyperv_vmbus.h |  3 +++
 3 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index addcef5..f7a1184 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c

@@ -854,12 +854,39 @@ void vmbus_initiate_unload(bool crash)
 static void vmbus_onoffer(struct vmbus_channel_message_header *hdr)
 {
 	struct vmbus_channel_offer_channel *offer;
-	struct vmbus_channel *newchannel;
+	struct vmbus_channel *oldchannel, *newchannel;
+	size_t offer_sz;

 	offer = (struct vmbus_channel_offer_channel *)hdr;

 	trace_vmbus_onoffer(offer);

+	mutex_lock(&vmbus_connection.channel_mutex);
+	oldchannel = find_primary_channel_by_offer(offer);
+	mutex_unlock(&vmbus_connection.channel_mutex);
+
+	if (oldchannel != NULL) {
+		atomic_dec(&vmbus_connection.offer_in_progress);
+
+		/*
+		 * We're resuming from hibernation: we expect the host to send
+		 * exactly the same offers that we had before the hibernation.
+		 */
+		offer_sz = sizeof(*offer);
+		if (memcmp(offer, &oldchannel->offermsg, offer_sz) == 0)
+			return;
+
+		pr_debug("Mismatched offer from the host (relid=%d)\n",
+			 offer->child_relid);
+
+		print_hex_dump_debug("Old vmbus offer: ", DUMP_PREFIX_OFFSET,
+				     16, 4, &oldchannel->offermsg, offer_sz,
+				     false);
+		print_hex_dump_debug("New vmbus offer: ", DUMP_PREFIX_OFFSET,
+				     16, 4, offer, offer_sz, false);
+		return;
+	}
+
 	/* Allocate the channel object and save this offer. */
 	newchannel = alloc_channel();
 	if (!newchannel) {

diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 09829e1..6c7a983 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c

@@ -337,6 +337,33 @@ struct vmbus_channel *relid2channel(u32 relid)
 }

 /*
+ * find_primary_channel_by_offer - Get the channel object given the new offer.
+ * This is only used in the resume path of hibernation.
+ */
+struct vmbus_channel *
+find_primary_channel_by_offer(const struct vmbus_channel_offer_channel *offer)
+{
+	struct vmbus_channel *channel;
+	const guid_t *inst1, *inst2;
+
+	WARN_ON(!mutex_is_locked(&vmbus_connection.channel_mutex));
+
+	/* Ignore sub-channel offers. */
+	if (offer->offer.sub_channel_index != 0)
+		return NULL;
+
+	list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) {
+		inst1 = &channel->offermsg.offer.if_instance;
+		inst2 = &offer->offer.if_instance;
+
+		if (guid_equal(inst1, inst2))
+			return channel;
+	}
+
+	return NULL;
+}

+
+/*
  * vmbus_on_event - Process a channel event notification
  *
  * For batched channels (default) optimize host to guest signaling

diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index 9f7fb6d..c42b46d 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h

@@ -310,6 +310,9 @@ int vmbus_add_channel_kobj(struct hv_device *device_obj,

 struct vmbus_channel *relid2channel(u32 relid);

+struct vmbus_channel *
+find_primary_channel_by_offer(const struct vmbus_channel_offer_channel *offer);
+
 void vmbus_free_channels(void);

 /* Connection interface */
--

1.8.3.1