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Re: [PATCH][4.16] x86/x2APIC: defer probe until after IOMMU ACPI table parsing


  • To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Thu, 4 Nov 2021 16:41:06 +0100
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  • Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxx>
  • Delivery-date: Thu, 04 Nov 2021 15:41:28 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 04.11.2021 15:21, Roger Pau Monné wrote:
> On Wed, Nov 03, 2021 at 03:40:55PM +0100, Jan Beulich wrote:
>> While commit XXXXXXXXXXXX ("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_boot_init() (which is what
>> calls acpi_iommu_init()), such that iommu_intremap getting disabled
>> there can be properly taken into account by apic_x2apic_probe().
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> LGTM. I cannot find any dependency between acpi_boot_init and having
> initialized the apic.

Sadly there is, and I've now learned that when believing I would test
the change yesterday I actually didn't (or else I would have spotted
the problem that I've spotted now), and instead I did boot an older
binary: acpi_process_madt() calls clustered_apic_check() and hence
relies on genapic to have got filled before.

I'll have to see if I can come up with some variant avoiding the issue,
but I suspect that's not going to be 4.16 material anymore then. My
first try is likely going to be to simply pull out acpi_iommu_init()
from acpi_boot_init().

Jan




 


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