Re: [PATCH 0/6] Enable SMM page level protection.

[Laszlo Ersek <lersek@redhat.com>]

On 11/04/16 14:50, Paolo Bonzini wrote:
> 
> 
> On 04/11/2016 14:28, Yao, Jiewen wrote:
>> I tried below way. But it does not help too much. It still takes more
>> than 1 minutes to boot with SMP=8.
>>
>>   SendSmiIpiAllExcludingSelf ();
>>   IoWrite8 (ICH9_APM_STS, DataPort    == NULL ? 0 : *DataPort);
>>   IoWrite8 (ICH9_APM_CNT, CommandPort == NULL ? 0 : *CommandPort);
>>
>> I also tried to reduce the timeout PCD to:
>>
>>   gUefiCpuPkgTokenSpaceGuid.PcdCpuSmmApSyncTimeout|1000
>>
>> However, I find CPU-2 is still missing.
>>
>> Maybe it is caused by QEMU emulate AP in serial mode, not parallel mode.
> 
> Yeah, that's possible without KVM.  Do you issue a PAUSE instruction in
> the spin loops?  That could help.

There's a BaseLib helper function for that BTW:

/**
  Requests CPU to pause for a short period of time.

  Requests CPU to pause for a short period of time. Typically used in MP
  systems to prevent memory starvation while waiting for a spin lock.

**/
VOID
EFIAPI
CpuPause (
  VOID
  );


The implementation in "MdePkg/Library/BaseLib/X64/GccInline.c" is

  __asm__ __volatile__ ("pause");

Thanks
Laszlo


>> I think it might be best choice to set PcdCpuSmmSyncMode|0x1
>>
>> It also helps cover a very corner case in SMM. J
>>