Re: [PATCH 01/11] arch: arm64: Export arch_smp_send_reschedule for mshv_vtl module

Naman Jain
2026-04-13T11:44:44Z

On 4/1/2026 10:24 PM, Michael Kelley wrote:
> From: Naman Jain <namjain@linux.microsoft.com> Sent: Monday, March 16, 2026 5:13 AM
>>
>
> Nit: For the patch "Subject", the most common prefix for the file
> arch/arm64/kernel/smp.c is "arm64: smp:". I'd suggest using that
> prefix for historical consistency.

Acked. Will change in v2.

>
>> mshv_vtl_main.c calls smp_send_reschedule() which expands to
>> arch_smp_send_reschedule(). When CONFIG_MSHV_VTL=m, the module cannot
>> access this symbol since it is not exported on arm64.
>>
>> smp_send_reschedule() is used in mshv_vtl_cancel() to interrupt a vCPU
>> thread running on another CPU. When a vCPU is looping in
>> mshv_vtl_ioctl_return_to_lower_vtl(), it checks a per-CPU cancel flag
>> before each VTL0 entry. Setting cancel=1 alone is not enough if the
>> target CPU thread is sleeping - the IPI from smp_send_reschedule() kicks
>> the remote CPU out of idle/sleep so it re-checks the cancel flag and
>> exits the loop promptly.
>>
>> Other architectures (riscv, loongarch, powerpc) already export this
>> symbol. Add the same EXPORT_SYMBOL_GPL for arm64. This is required
>> for adding arm64 support in MSHV_VTL.
>>
>> Signed-off-by: Naman Jain <namjain@linux.microsoft.com>
>> ---
>> arch/arm64/kernel/smp.c | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
>> index 1aa324104afb..26b1a4456ceb 100644
>> --- a/arch/arm64/kernel/smp.c
>> +++ b/arch/arm64/kernel/smp.c
>> @@ -1152,6 +1152,7 @@ void arch_smp_send_reschedule(int cpu)
>> {
>> smp_cross_call(cpumask_of(cpu), IPI_RESCHEDULE);
>> }
>> +EXPORT_SYMBOL_GPL(arch_smp_send_reschedule);
>>
>> #ifdef CONFIG_ARM64_ACPI_PARKING_PROTOCOL
>> void arch_send_wakeup_ipi(unsigned int cpu)
>> --
>> 2.43.0
>>
>
> The "Subject" nit notwithstanding,
>
> Reviewed-by: Michael Kelley <mhklinux@outlook.com>

Thanks,
Naman