Re: [Xen-devel] [PATCH 1/2] hvmloader: limit CPUs exposed to guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.06.16 at 17:37, <boris.ostrovsky@xxxxxxxxxx> wrote:
> On 06/16/2016 11:25 AM, Jan Beulich wrote:
>>>>> On 16.06.16 at 17:09, <boris.ostrovsky@xxxxxxxxxx> wrote:
>>> On 06/16/2016 05:40 AM, Jan Beulich wrote:
>>>
>>> --- a/tools/firmware/hvmloader/acpi/mk_dsdt.c
>>> +++ b/tools/firmware/hvmloader/acpi/mk_dsdt.c
>>> @@ -150,6 +150,14 @@ int main(int argc, char **argv)
>>>      indent(); printf("MSU, 8\n");
>>>      pop_block();
>>>  
>>> +    /* Processor object helpers. */
>>> +    push_block("Method", "PMAT, 2");
>>> +    push_block("If", "LLess(Arg0, NCPU)");
>>> +    stmt("Return", "ToBuffer(Arg1)");
>>> +    pop_block();
>>> +    stmt("Return", "Buffer() {0, 8, 0xff, 0xff, 0, 0, 0, 0}");
>>>
>>>
>>> Could you explain what this is? (I suspect  this is related to MAT
>>> object and I don't think I understand what it is).
>> This is a helper routine for _MAT(), helping greatly to reduce
>> overall size of the DSDT. It checks whether the CPU is within the
>> range of available ones (online or offline), and if it isn't returns a
>> static buffer instead of data read from MADT (as it's the purpose
>> of this patch to remove these MADT entries for not present CPUs).
> 
> I meant just the last line (I understand what the routine is --- I am
> not clear where MAT format is defined).

That's a MADT entry of type ACPI_MADT_TYPE_LOCAL_APIC. Basically
an equivalent of the ToBuffer(MAT) used previously (and now still used
for CPU0).

Jan


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