2019-10-15 12:17:10

by Andrea Parri

Subject: [PATCH v3 3/3] Drivers: hv: vmbus: Add module parameter to cap the VMBus version

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 <[email protected]>
Signed-off-by: Andrea Parri <[email protected]>
---
drivers/hv/connection.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index cadfb34b38d80..0475be4356dd7 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;
@@ -240,6 +251,8 @@ int vmbus_connect(void)
goto cleanup;

version = vmbus_versions[i];
+ if (version > max_version)
+ continue;

ret = vmbus_negotiate_version(msginfo, version);
if (ret == -ETIMEDOUT)
--
2.23.0

2019-10-15 13:16:43

by Michael Kelley (LINUX)

Subject: RE: [PATCH v3 3/3] Drivers: hv: vmbus: Add module parameter to cap the VMBus version

From: Andrea Parri <[email protected]> Sent: Tuesday, October 15, 2019 4:47 AM
>
> 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 <[email protected]>
> Signed-off-by: Andrea Parri <[email protected]>
> ---
> drivers/hv/connection.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>

Reviewed-by: Michael Kelley <[email protected]>