CVE-2026-90097

In the Linux kernel, the following vulnerability has been resolved:

Drivers: hv: vmbus: Skip VMBus module cleanup for non-nested root partition

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.