Drivers: hv: Add Hyper-V balloon driver

Add the basic balloon driver. Windows hosts dynamically manage the guest
memory allocation via a combination memory hot add and ballooning. Memory
hot add is used to grow the guest memory upto the maximum memory that can be
allocatted to the guest. Ballooning is used to both shrink as well as expand
up to the max memory. Supporting hot add needs additional support from the
host. We will support hot add when this support is available. For now,
by setting the VM startup memory to the VM  max memory, we can use
ballooning alone to dynamically manage memory allocation amongst
competing guests on a given host.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hv/Kconfig

@@ -13,4 +13,10 @@ config HYPERV_UTILS
 	help
 	  Select this option to enable the Hyper-V Utilities.
 
+config HYPERV_BALLOON
+	tristate "Microsoft Hyper-V Balloon driver"
+	depends on HYPERV
+	help
+	  Select this option to enable Hyper-V Balloon driver.
+
 endmenu

drivers/hv/Makefile

@@ -1,5 +1,6 @@
 obj-$(CONFIG_HYPERV)		+= hv_vmbus.o
 obj-$(CONFIG_HYPERV_UTILS)	+= hv_utils.o
+obj-$(CONFIG_HYPERV_BALLOON)	+= hv_balloon.o
 
 hv_vmbus-y := vmbus_drv.o \
 		 hv.o connection.o channel.o \