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

["Gao, Liming" <liming.gao@intel.com>]

> -----Original Message-----
> From: Justen, Jordan L
> Sent: Thursday, March 9, 2017 2:59 AM
> To: Gao, Liming <liming.gao@intel.com>; Kinney, Michael D <michael.d.kinney@intel.com>; edk2-devel@lists.01.org; Brijesh Singh
> <brijesh.ksingh@gmail.com>; Laszlo Ersek <lersek@redhat.com>
> Cc: Thomas.Lendacky@amd.com; leo.duran@amd.com; brijesh.sing@amd.com
> Subject: RE: [RFC PATCH v1 4/5] OvmfPkg/BaseIoLibIntrinsic: import BaseIoLibIntrinsic package
> 
> 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

I get your point. So, I suggest to always check SEV in BaseIoLib. If people meet with the performance issue, DXE/SMM version IoLib can be added later.