Re: [PATCH v3 1/1] Drivers: hv: vmbus: Skip VMBus module cleanup for non-nested root partition

[Wei Liu <wei.liu@kernel.org>]

On Wed, Aug 12, 2026 at 07:52:23AM -0700, Michael Kelley wrote:
> The VMBus module initialization function, hv_acpi_init(), currently
> does nothing when running in the root partition and root is not nested
> in another VM. But the initialization function reports success, so the
> VMBus module is indeed loaded. VMBus functionality is not actually
> needed, but the VMBus module must be loaded so that hv_vmbus_exists()
> can answer correctly. Furthermore, the mshv_root dependency on the
> VMBus module is needed as described in the commit message for
> 840b740a35bf ("mshv: Add conditional VMBus dependency").
> 
> Loading the VMBus module without actually initializing it causes
> failures if the module should later be unloaded. The module unload code
> tries to clean up things that were never initialized, resulting in
> memory faults and a panic.
> 
> Fix this by having VMBus module exit function perform the same
> check for non-nested root partition, and do nothing in such a
> case, just like hv_acpi_init().
> 
> In the long run, the code that manages the Hyper-V provided SynIC
> should be refactored to better coordinate the requirements of
> root partition scenarios and normal VM scenarios, and to hopefully
> remove the hv_vmbus_exists() dependnecy between mshv_root and
> VMBus modules. Preventing the current unload failure scenario is
> an expediency until such a refactoring is done.
> 
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Closes: https://lore.kernel.org/linux-hyperv/20260721154943.A09BD1F00A3D@smtp.kernel.org/
> Fixes: 7e279d78664aa ("Drivers: hv: vmbus: skip VMBus initialization if Linux is root")
> Signed-off-by: Michael Kelley <mhklinux@outlook.com>
> Reviewed-by: Easwar Hariharan <easwar.hariharan@linux.microsoft.com>

Applied. Thanks.