Re: [Xen-devel] [PATCH RFC 5/9] x86/traps: Functional prep work

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.05.14 at 12:45, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 15/05/14 11:36, Jan Beulich wrote:
>>>>> On 15.05.14 at 11:48, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> --- a/xen/arch/x86/setup.c
>>> +++ b/xen/arch/x86/setup.c
>>> @@ -558,6 +558,12 @@ void __init noreturn __start_xen(unsigned long mbi_p)
>>>          .stop_bits = 1
>>>      };
>>>  
>>> +    set_processor_id(0);
>>> +    set_current((struct vcpu *)0xfffff000); /* debug sanity */
>>> +    this_cpu(curr_vcpu) = idle_vcpu[0] = current;
>> The this_cpu() part wasn't there in the original code - is that really
>> needed, and ...
> 
> I was attempting to go for similarity between __start_xen and
> start_secondary, which reminds me I need a further fix regarding cr4,
> which still loads CR4.MCE on APs before having a TRAP_machine_check
> handler available.
> 
>>
>>> +
>>> +    sort_exception_tables();
>>> +
>>>      percpu_init_areas();
>> ... is that really safe/meaningful before this function got called?
> 
> There is no specific relationship between sort_exception_tables() and
> percpu_init_areas(), both of which are tweaking well defined state
> inside the .data section.
> 
> sort_excetpion_tables() is a prerequisite for getting extable fixups to
> work in the trap handlers, but as indicated, it would be nice to turn it
> into something more like "assert exception tables are sorted" and making
> the linker do the work.

The comment wasn't about sort_exception_tables(), but about the
(at least apparent) conflict of this_cpu() getting used before
percpu_init_areas().

Jan


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