Re: [Xen-devel] Linux as 32-bit Dom0?

[Juergen Gross <jgross@xxxxxxxx>]

On 22/11/17 15:48, Jan Beulich wrote:
>>>> On 22.11.17 at 15:40, <jgross@xxxxxxxx> wrote:
>> On 22/11/17 15:05, Jan Beulich wrote:
>>> Jürgen, Boris,
>>>
>>> am I trying something that's not allowed, but selectable via Kconfig?
>>> On system with multiple IO-APICs (I assume that's what triggers the
>>> problem) I get
>>>
>>> Kernel panic - not syncing: Max apic_id exceeded!
>>
>> Generally I don't think 32 bit dom0 is forbidden, but rarely used. I
>> wouldn't be too sad in case we'd decide to drop that support. ;-)
>>
>> Can you please be a little bit more specific?
>>
>> How many IOAPICs? From the code I guess this is an INTEL system with not
>> too recent IOAPIC versions (<0x14)?
>>
>> Having a little bit more of the boot log might help, too.
> 
> Full log attached, which should answer all questions. This is
> a Haswell system, so not too old an IO-APIC flavor I would say.

From this data I can't explain why the system is crashing.

Right now I have 3 possible explanations, all could be proofed by
adding some printk statements in io_apic_get_unique_id(). Could you
please print the value returned by get_physical_broadcast() and the
complete apic_id_map right before the panic() call?

The possibilities IMHO are:
- the LAPIC version is limiting the number of available apicids
- apic_id_map is somehow filled up completely with all bits set
- a compiler bug leading to a false positive


Juergen



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