Re: [RFC PATCH v1 4/5] OvmfPkg/BaseIoLibIntrinsic: import BaseIoLibIntrinsic package

[Jordan Justen <jordan.l.justen@intel.com>]

On 2017-03-08 07:41:58, Gao, Liming wrote:
> 
> >-----Original Message-----
> >From: Justen, Jordan L
> 
> >One other thought is, should we consider a DxeSmm alternative .inf for
> >BaseIoLibIntrinsic.inf? In that case we could use a global variable to
> >help out. Maybe this could prevent the concern that might drive a new
> >PCD to be added?
> >
> >-Jordan
> Current patch has stored the check state into data section. In PEI
> phase, the data section can't be written. So, every call will check
> CpuId. In DXE and SMM phase, the data section can be written. The
> first call will cache the check state. So, no DxeSmm INF is
> required.
> 

I don't think we can attempt to write a variable to memory in generic
SEC/PEI code. Some flash memory treat memory writes as an I/O for
programming purposes. I think we added
PcdGuidedExtractHandlerTableAddress for this reason. This is why I
suggested that maybe we could add a DXE/SMM .inf where we could assume
writeable global variables exit.

-Jordan