From: Easwar Hariharan <[email protected]> Sent: Tuesday, August 4, 2026 12:40 PM > > On 8/4/2026 12:05, Michael Kelley wrote: > > The VMBus module should not be loaded when Linux is running directly > > in the root partition and root is not nested in another VM. Current > > code checks this condition and skips VMBus module initialization, which > > works. But it returns 0 as the result, so Linux thinks the module has > > successfully loaded. Later, if the module were to be unloaded, the > > VMBus 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 initialization return -ENODEV for this > > case. The module is then not loaded, and the unload path can never run. > > > > Reported-by: Sashiko <[email protected]> > > Closes: https://lore.kernel.org/linux- > hyperv/[email protected]/ > > Fixes: 7e279d78664aa ("Drivers: hv: vmbus: skip VMBus initialization if > > Linux is root") > > Signed-off-by: Michael Kelley <[email protected]> > > --- > > drivers/hv/vmbus_drv.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c > > index e19ec73b0187..849d7e1a7320 100644 > > --- a/drivers/hv/vmbus_drv.c > > +++ b/drivers/hv/vmbus_drv.c > > @@ -2976,7 +2976,7 @@ static int __init hv_acpi_init(void) > > return -ENODEV; > > > > if (hv_root_partition() && !hv_nested) > > - return 0; > > + return -ENODEV; > > > > /* > > * Get ACPI resources first. > > This seems straightforward:
Alas, it's not so straightforward, as Sashiko pointed out. I knew that the mshv module has a dependency on the vmbus module, but had forgotten. There's a reason for the dependency as described in the commit message for 840b740a35bf. There's another easy way to fix the VMBus module unload problem. I'll send a v2. :-) Michael > > > Reviewed-by: Easwar Hariharan <[email protected]>
