Re: [PATCH 06/11] Drivers: hv: Make sint vector architecture neutral in MSHV_VTL

Naman Jain
2026-04-13T11:47:58Z

On 4/1/2026 10:27 PM, Michael Kelley wrote:
> From: Naman Jain <namjain@linux.microsoft.com> 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.

Regarding memory leak on cpu offline/online or module load/unload- it is
beyond the scope of this series, I will fix it separately.

I may need some more time in addressing comments on rest of the patches.
Please bear with me.

Regards,
Naman

>
>>
>> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
>> Signed-off-by: Naman Jain <namjain@linux.microsoft.com>
>> ---
>> drivers/hv/mshv_vtl_main.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/hv/mshv_vtl_main.c b/drivers/hv/mshv_vtl_main.c
>> index b607b6e7e121..91517b45d526 100644
>> --- a/drivers/hv/mshv_vtl_main.c
>> +++ b/drivers/hv/mshv_vtl_main.c
>> @@ -234,7 +234,7 @@ static void mshv_vtl_synic_enable_regs(unsigned int cpu)
>> union hv_synic_sint sint;
>>
>> sint.as_uint64 = 0;
>> - sint.vector = HYPERVISOR_CALLBACK_VECTOR;
>> + sint.vector = vmbus_interrupt;
>> sint.masked = false;
>> sint.auto_eoi = hv_recommend_using_aeoi();
>>
>> @@ -753,7 +753,7 @@ static void mshv_vtl_synic_mask_vmbus_sint(void *info)
>> const u8 *mask = info;
>>
>> sint.as_uint64 = 0;
>> - sint.vector = HYPERVISOR_CALLBACK_VECTOR;
>> + sint.vector = vmbus_interrupt;
>> sint.masked = (*mask != 0);
>> sint.auto_eoi = hv_recommend_using_aeoi();
>>
>> --
>> 2.43.0
>>
>
> Assuming there's no timing problem vs. the VMBus driver,
>
> Reviewed-by: Michael Kelley <mhklinux@outlook.com>