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

[Kevin O'Connor]

On Tue, Jan 31, 2017 at 04:38:04PM +0000, Sironi, Filippo wrote:
> > On 27 Jan 2017, at 06:27, Kevin O'Connor <kevin at koconnor.net> 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.
> 
> What if someone is using SeaBIOS but isn't using QEMU?

The fw/acpi.c code is only ever active on QEMU.

-Kevin