Re: [PATCH v2.2 1/6][4.16?] x86/x2APIC: defer probe until after IOMMU ACPI table parsing

[Jan Beulich <jbeulich@suse.com>]

On 15.11.2021 16:07, Roger Pau Monné wrote:
> On Mon, Nov 15, 2021 at 03:31:39PM +0100, Jan Beulich wrote:
>> While commit 46c4061cd2bf ("x86/IOMMU: mark IOMMU / intremap not in use
>> when ACPI tables are missing") deals with apic_x2apic_probe() as called
>> from x2apic_bsp_setup(), the check_x2apic_preenabled() path is similarly
>> affected: The call needs to occur after acpi_iommu_init(), such that
>> iommu_intremap getting disabled there can be properly taken into account
>> by apic_x2apic_probe().
>>
>> Note that, for the time being (further cleanup patches following),
>> reversing the order of the calls to generic_apic_probe() and
>> acpi_boot_init() is not an option:
>> - acpi_process_madt() calls clustered_apic_check() and hence relies on
>>   genapic to have got filled before,
>> - generic_bigsmp_probe() (called from acpi_process_madt()) needs to
>>   occur after generic_apic_probe(),
>> - acpi_parse_madt() (called from acpi_process_madt()) calls
>>   acpi_madt_oem_check(), which wants to be after generic_apic_probe().
>>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> 
> Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

Thanks.

>> --- a/xen/arch/x86/setup.c
>> +++ b/xen/arch/x86/setup.c
>> @@ -1700,15 +1700,30 @@ void __init noreturn __start_xen(unsigne
>>  
>>      dmi_scan_machine();
>>  
>> -    generic_apic_probe();
>> -
>>      mmio_ro_ranges = rangeset_new(NULL, "r/o mmio ranges",
>>                                    RANGESETF_prettyprint_hex);
>>  
>>      xsm_multiboot_init(module_map, mbi);
>>  
>> +    /*
>> +     * IOMMU-related ACPI table parsing may require some of the system domains
>> +     * to be usable.
> 
> I would be a bit more specific and likely add "...to be usable in
> order to hide IOMMU PCI devices.".

Hmm, not sure. I did specifically leave out the "why" part, as dom_io
might also become required for something. If you nevertheless think
I should extend the comment, then I'd insist on using "e.g." just
like I did in the comment next to the call to generic_apic_probe().

Jan