On 4/13/2026 9:19 PM, Michael Kelley wrote:
From: Naman Jain <[email protected]> Sent: Monday, April 13, 2026
4:48 AM
On 4/1/2026 10:27 PM, Michael Kelley wrote:
From: Naman Jain <[email protected]> Sent: Monday, March 16, 2026
5:13 AM
Generalize Synthetic interrupt source vector (sint) to use
vmbus_interrupt variable instead, which automatically takes care of
architectures where HYPERVISOR_CALLBACK_VECTOR is not present (arm64).
Sashiko AI raised an interesting question about the startup timing --
whether the vmbus_platform_driver_probe() is guaranteed to have
set vmbus_interrupt before the VTL functions below run and use it.
What causes the mshv_vtl.ko module to be loaded, and hence run
mshv_vtl_init()?
There is no race condition here. The init ordering guarantees that
vmbus_interrupt is always set before mshv_vtl_synic_enable_regs()
reads it.
The call chain for setting vmbus_interrupt:
subsys_initcall(hv_acpi_init) [level 4]
-> platform_driver_register(&vmbus_platform_driver) and so on.
The call chain for reading vmbus_interrupt:
module_init(mshv_vtl_init) [level 6]
-> hv_vtl_setup_synic()
-> cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, ..., mshv_vtl_alloc_context,
...)
-> mshv_vtl_alloc_context()
-> mshv_vtl_synic_enable_regs()
-> sint.vector = vmbus_interrupt
do_initcalls() processes sections in order 0 through 7, so
hv_acpi_init() (level 4) is guaranteed to complete before
mshv_vtl_init() (level 6) runs.
I think the situation is more complex than what you describe, depending
on whether the VMBus driver and/or MSHV_VTL are built as modules vs.
being built-in to the kernel image. In include/linux/module.h, see the
comment for module_init() and how subsys_initcall() is mapped
to module_init() when built as a module.
If both are built-in, then what you describe is correct. But if either or
both are modules, then the respective init functions (hv_acpi_init
and mshv_vtl_init) get called at the time the module is loaded, and
not by do_initcalls(). I think hv_vmbus.ko gets loaded when an attempt
is first made to access a disk, but I would need to look more closely to
be sure. I don't have any understanding of what causes mshv_vtl.ko
to be loaded. And what is the ordering if MSHV_VTL is built-in while
VMBus is built as a module, or vice versa?
Michael
Based on this, I still feel that this race is not possible.
hv_vmbus mshv_vtl
y y -> different initcall levels, no issues
y m -> use without initialization is not possible
m y -> config dependencies take care of this, and mshv_vtl
is forced to compile as a module in this case.
m m -> config and symbol dependencies should take care of
it. mshv_vtl has symbol and config dependencies on hv_vmbus, and it
won't allow loading mshv_vtl if hv_vmbus module is not loaded.
Relevant code here: kernel/module/main.c
Regards,
Naman
