Currently, Linux guests negotiate the VMBus version with Hyper-V and use the highest available VMBus version they can connect to. This has some drawbacks: by using the highest available version, certain code paths are never executed and can not be tested when the guest runs on the newest host. Add the module parameter "max_version", to upper-bound the VMBus versions guests can negotiate. Suggested-by: Dexuan Cui <decui@xxxxxxxxxxxxx> Signed-off-by: Andrea Parri <parri.andrea@xxxxxxxxx> --- drivers/hv/connection.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c index 2f6961ac8c996..f60d7330ff3fd 100644 --- a/drivers/hv/connection.c +++ b/drivers/hv/connection.c @@ -14,6 +14,7 @@ #include <linux/wait.h> #include <linux/delay.h> #include <linux/mm.h> +#include <linux/module.h> #include <linux/slab.h> #include <linux/vmalloc.h> #include <linux/hyperv.h> @@ -55,6 +56,16 @@ static __u32 vmbus_versions[] = { VERSION_WS2008 }; +/* + * Maximal VMBus protocol version guests can negotiate. Useful to cap the + * VMBus version for testing and debugging purpose. + */ +static uint max_version = VERSION_WIN10_V5_2; + +module_param(max_version, uint, S_IRUGO); +MODULE_PARM_DESC(max_version, + "Maximal VMBus protocol version which can be negotiated"); + int vmbus_negotiate_version(struct vmbus_channel_msginfo *msginfo, u32 version) { int ret = 0; @@ -237,6 +248,8 @@ int vmbus_connect(void) for (i = 0; i < ARRAY_SIZE(vmbus_versions); i++) { version = vmbus_versions[i]; + if (version > max_version) + continue; ret = vmbus_negotiate_version(msginfo, version); if (ret == -ETIMEDOUT) -- 2.23.0