[PATCH 1/1] Drivers: hv: balloon: Enable dynamic memory protocol negotiation with Windows 10 hosts

[alexng@microsoft.com]

From: Alex Ng <alexng@microsoft.com>

This enables dynamic protocol support on Windows 10 Hyper-V hosts. 
If the host does not support Windows 10 protocol, then it falls back to
previous versions.

The change allows guests on Windows 10 Hyper-V hosts to hot-add memory 
even when dynamic memory is not enabled on the guest.

Signed-off-by: Alex Ng <alexng@microsoft.com>
---
 drivers/hv/hv_balloon.c | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index cb5b7dc..15be14b 100644
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -62,11 +62,13 @@
 enum {
 	DYNMEM_PROTOCOL_VERSION_1 = DYNMEM_MAKE_VERSION(0, 3),
 	DYNMEM_PROTOCOL_VERSION_2 = DYNMEM_MAKE_VERSION(1, 0),
+	DYNMEM_PROTOCOL_VERSION_3 = DYNMEM_MAKE_VERSION(2, 0),
 
 	DYNMEM_PROTOCOL_VERSION_WIN7 = DYNMEM_PROTOCOL_VERSION_1,
 	DYNMEM_PROTOCOL_VERSION_WIN8 = DYNMEM_PROTOCOL_VERSION_2,
+	DYNMEM_PROTOCOL_VERSION_WIN10 = DYNMEM_PROTOCOL_VERSION_3,
 
-	DYNMEM_PROTOCOL_VERSION_CURRENT = DYNMEM_PROTOCOL_VERSION_WIN8
+	DYNMEM_PROTOCOL_VERSION_CURRENT = DYNMEM_PROTOCOL_VERSION_WIN10
 };
 
 
@@ -1294,13 +1296,25 @@ static void version_resp(struct hv_dynmem_device *dm,
 	if (dm->next_version == 0)
 		goto version_error;
 
-	dm->next_version = 0;
 	memset(&version_req, 0, sizeof(struct dm_version_request));
 	version_req.hdr.type = DM_VERSION_REQUEST;
 	version_req.hdr.size = sizeof(struct dm_version_request);
 	version_req.hdr.trans_id = atomic_inc_return(&trans_id);
-	version_req.version.version = DYNMEM_PROTOCOL_VERSION_WIN7;
-	version_req.is_last_attempt = 1;
+	version_req.version.version = dm->next_version;
+
+	/*
+	 * Set the next version to try in case current version fails.
+	 * Win7 protocol ought to be the last one to try.
+	 */
+	if (version_req.version.version == DYNMEM_PROTOCOL_VERSION_WIN8) {
+		dm->next_version = DYNMEM_PROTOCOL_VERSION_WIN7;
+		version_req.is_last_attempt = 0;
+	} else if (version_req.version.version ==
+		   DYNMEM_PROTOCOL_VERSION_WIN7) {
+
+		dm->next_version = 0;
+		version_req.is_last_attempt = 1;
+	}
 
 	ret = vmbus_sendpacket(dm->dev->channel, &version_req,
 				sizeof(struct dm_version_request),
@@ -1440,7 +1454,7 @@ static int balloon_probe(struct hv_device *dev,
 
 	dm_device.dev = dev;
 	dm_device.state = DM_INITIALIZING;
-	dm_device.next_version = DYNMEM_PROTOCOL_VERSION_WIN7;
+	dm_device.next_version = DYNMEM_PROTOCOL_VERSION_WIN8;
 	init_completion(&dm_device.host_event);
 	init_completion(&dm_device.config_event);
 	INIT_LIST_HEAD(&dm_device.ha_region_list);
@@ -1472,7 +1486,7 @@ static int balloon_probe(struct hv_device *dev,
 	version_req.hdr.type = DM_VERSION_REQUEST;
 	version_req.hdr.size = sizeof(struct dm_version_request);
 	version_req.hdr.trans_id = atomic_inc_return(&trans_id);
-	version_req.version.version = DYNMEM_PROTOCOL_VERSION_WIN8;
+	version_req.version.version = DYNMEM_PROTOCOL_VERSION_WIN10;
 	version_req.is_last_attempt = 0;
 
 	ret = vmbus_sendpacket(dev->channel, &version_req,
-- 
1.8.5.2