Re: [edk2-devel] [edk2] AP core : call GetPeiServicesTablePointer function hang

["Tiger Liu(BJ-RD)" <tigerliu@zhaoxin.com>]

Hi, Mike:
Got it!
Thank you very much!

I have another question:
Why does AP use an IDT table which is different with BSP?
Is there other concern?

Thanks
-----邮件原件-----
发件人: Kinney, Michael D <michael.d.kinney@intel.com>
发送时间: 2019年11月19日 0:27
收件人: devel@edk2.groups.io; Tiger Liu(BJ-RD) <TigerLiu@zhaoxin.com>; Kinney, Michael D <michael.d.kinney@intel.com>
主题: RE: [edk2-devel] [edk2] AP core : call GetPeiServicesTablePointer function hang

PEI Phase execution environment is focused on BSP execution.
The PEI Services and most of the PPI services are not designed to be MP safe.  Since it is not safe for an AP to call PEI Services, the IDT entry with the pointer to the PEI Service Table is not available to an AP to prevent code from incorrectly calling a PEI Service from an AP.

It is legal to run code on an AP in the PEI Phase, but the code executed must be carefully designed to not use PEI Services and is usually designed to execute using only stack/memory and system resources that have assigned for exclusive access by an AP.
This is usually communicated from BSP to an AP through a mailbox in memory.  If an AP needs something like a PEI Service (e.g.
memory allocation or logging), then the AP should make that request to the BSP to perform that operation for the AP.

Mike

> -----Original Message-----
> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Tiger
> Liu(BJ-RD)
> Sent: Monday, November 18, 2019 1:08 AM
> To: devel@edk2.groups.io
> Subject: [edk2-devel] [edk2] AP core : call GetPeiServicesTablePointer
> function hang
>
> Dear All:
> I met a question during debug multi-processor code.
>
> I found if AP's procedure call
> GetPeiServicesTablePointer function , then it would hang.
> GetPeiServicesTablePointer (
>   VOID
>   )
> {
>   CONST EFI_PEI_SERVICES  **PeiServices;
>   IA32_DESCRIPTOR   Idtr;
>
>   AsmReadIdtr (&Idtr);
>   PeiServices = (CONST EFI_PEI_SERVICES **) (*(UINTN*)(Idtr.Base -
> sizeof (UINTN)));
>   ASSERT (PeiServices != NULL);
>   return PeiServices;
> }
>
> It seems BSP and AP use different IDT table? Why?
>
> Thanks
>
>
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CONFIDENTIAL NOTE:
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