On Wed, Jan 27, 2021 at 12:23:45PM -0800, Michael Kelley wrote: [...] > +static int hv_setup_stimer0_irq(void) > +{ > + int ret; > + > + ret = acpi_register_gsi(NULL, HYPERV_STIMER0_VECTOR, > + ACPI_EDGE_SENSITIVE, ACPI_ACTIVE_HIGH); When IO-APIC is enabled on x86, acpi_register_gsi calls mp_map_gsi_to_irq. That function then calls mp_find_ioapic. Is HYPERV_STIMER0_VECTOR, when used as a GSI, associated with an IO-APIC? If not, wouldn't mp_find_ioapic return an error causing acpi_register_gsi to fail? Ah, it appears that this function is not called on x86. I haven't checked how ARM handles GSI, but presumably this works for you. It would be good if a comment can be added to clarify things. Wei.