Re: [SeaBIOS] [PATCH v2 0/4] support booting more than 255 CPUs with QEMU

[Laszlo Ersek]

On 06/20/16 13:15, Igor Mammedov wrote:
  On Mon, 20 Jun 2016 10:45:37 +0200
 Gerd Hoffmann <kraxel(a)redhat.com> wrote:
 
  On Mo, 2016-05-16 at 21:00 -0400, Kevin
O'Connor wrote:
  On Wed, May 11, 2016 at 12:03:37PM +0200, Igor
Mammedov wrote:
  Changelog since:
   v1:
     * s/count_cpu/apic_id_init/
     * merge handle_x2apic() into apic_id_init()
   RFC:
     * move out max-cpus check out of mptable_setup()
     * factor out CPU counting/apic ID detection in separate
 function
     * return back accidentially deleted debug message with APIC ID
     * drop unused code in smp_setup()
     
 According to SDM, if CPUs have APIC ID more than 254
 firmware should pass control to OS in x2APIC mode.
 This series adds x2APIC bootstrap initialization.

 QEMU side of x2APIC support:
 https://lists.gnu.org/archive/html/qemu-devel/2016-05/msg01094.html
 Thanks Igor.  The first 3 patches look good to me.  I'll commit to
 SeaBIOS once the corresponding QEMU support is accepted.
 Ping.  What is the status of this in qemu?  qemu 2.7 soft freeze is
 coming, and it is about time to plan the seabios update (1.9.3
 release).
 I need to dust RFC off and respin as Paolo wanted to sync APIC ID
 other way than in RFC and also on list there is v2 ACPI refactoring
 that x2APIC enablement depends on.
 
 Laszlo,
 wrt OVMF does suggested here fw_Cfg interface look ok to you?
I checked your v2 series quickly, with more attention to "etc/boot-cpus"
and patch #3.

I also re-read your argument in
<20160509172828.0d839294(a)nial.brq.redhat.com>om>:

  Reasons, I've skipped CPUID[0xb]:edx is not
because it's currently not
 supported but rather:
  1st: we already have 'etc/max-cpus' which is 'max possible APIC ID +
       1', so reuse it.
  2nd: beside complicating(making it longer, timewise) AP bootstrap,
       detection at runtime wouldn't work in case of CPU hotplug as it
       won't detect x2APIC CPUs if they are not yet present. real HW
       might work around this issue just hardcodding what APIC mode it
       wants as possible APIC IDs are known in advance for a particular
       board.
I think it should be okay.

For OVMF I have no idea yet how we're going to accommodate this.
Minimally it will depend on fixing
<https://github.com/tianocore/edk2/issues/87> in UefiCpuPkg. But, the
"etc/boot-cpus" interface looks sane to me.

Thanks
Laszlo