[SeaBIOS] [PATCH 1/2] fw/acpi: Build MADT the way commodity BIOSes do

[Laszlo Ersek]

On 01/27/17 15:57, Laszlo Ersek wrote:
> On 01/27/17 15:27, Kevin O'Connor wrote:
>> On Fri, Jan 27, 2017 at 02:18:39AM +0100, Filippo Sironi wrote:
>>> When running Linux on an Intel machine with a commodity BIOS, CPUs are
>>> numbered starting from 0 and the first half refers to the first logical
>>> CPU on each core while the second half refers to the second logical CPU
>>> on each core.
>>> As an example, on machine with 2 sockets, 4 cores per socket, and 2
>>> logical CPUs per core, CPUs would be numbered:
>>>
>>> *  0  1  2  3 - first logical CPU on each core of socket 0
>>> *  4  5  6  7 - first logical CPU on each core of socket 1
>>> *  8  9 10 11 - second logical CPU on each core of socket 0
>>> * 12 13 14 15 - second logical CPU on each core of socket 1
>>>
>>> With seabios (prior to this patch), CPU 0 would be the first logical CPU
>>> on core 0 of socket 0, CPU 1 would be the second logical CPU on core 0
>>> of socket 0, and so on.
>>> This is due to the fact that processor_id and local_apic_id are assigned
>>> with the same value when building MADT.
>>>
>>> Exhaust the most-significant 7 bits of the 8-bit APIC ID and then come
>>> back to the least-significant bit when assigning local_apic_id, since
>>> the least-significant bit identifies the second logical CPU on a core.
>>>
>>> If HTT isn't available, keep the previous behavior.
>>>
>>> Signed-off-by: Filippo Sironi <sironi at amazon.de>
>>> ---
>>>  src/fw/acpi.c | 42 +++++++++++++++++++++++++++++++++++++++++-
>>>  1 file changed, 41 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/src/fw/acpi.c b/src/fw/acpi.c
>>> index 8bc2ca6..864c247 100644
>>> --- a/src/fw/acpi.c
>>> +++ b/src/fw/acpi.c
>>
>> The acpi.c code in seabios is deprecated.  With all recent version of
>> qemu/kvm the acpi tables are obtained from qemu.  So, if there is a
>> desired change to the tables then a patch should be made for qemu.
> 
> QEMU constructs minimal / condensed APIC IDs so that they precisely
> correspond to the socket / core / thread hierarchy requested on the
> command line. If I remember correctly, the algorithm was implemented
> directly from Intel's MP spec. If the APIC IDs in the guest don't look
> as desired, I think the -smp option might have to be tweaked.

... by that I attempted (and failed) to say that the error is likely on
the concrete QEMU command line, not in the code.

> 
> I also seem to recall that this spec-adherent behavior could be machine
> type dependent (i.e., unavailable before a specific machine type). The
> machtypes not conforming to it should be ancient IMO.
> 
> CC'ing Eduardo and Igor.
> 
> Thanks
> Laszlo
>