Re: [PATCH] kvm: bios: Put AP boot up code to 0x1000

["Sebastian Herbszt" <herbszt@gmx.de>]

Yang, Sheng wrote:
> Please refer to my another patch comment. Basicly, AP is running HLT 
> in 0x10038, but it can exit due to some reason, here QEmu want to 
> raise it up . But after AP exit from HLT, it can't return to it 
> because the code was overrided by grub and no HLT loop there. Then AP 
> had gone away...

Thank you for pointing me to "[PATCH] KVM: Fix QEmu interrupted HLT
emulation". You wrote there:
"Though I also sent a patch for BIOS, it's necessary to get correct behavior here."

Would i be correct saying the problem is kvm/qemu only and with that patch
applied the bios fix is not needed?

If you still want to change the bios code i would suggest jumping to the
original smp_ap_boot_code location in rombios32.bin which should not
get overwritten. The following patch is based on the bochs version.

- Sebastian

--- rombios32start.orig 2008-08-02 19:37:34.000000000 +0200
+++ rombios32start.S    2008-08-02 20:19:15.000000000 +0200
@@ -40,9 +40,11 @@

   .code16
 smp_ap_boot_code_start:
+  cli
   xor %ax, %ax
   mov %ax, %ds
   lock incw CPU_COUNT_ADDR
+  ljmp $0xe000, $(1f-_start)
 1:
   hlt
   jmp 1b