Re: [edk2-devel] [PATCH 1/1] OvmfPkg: Reserve the Ovmf work area as RT_DATA

["Gerd Hoffmann" <kraxel@redhat.com>]

  Hi,

> > Runtime service call are restricted so that you don't have concurrent threads
> > executing (see section 8.1 of the specification). Without that you would have
> > problems with runtime services today.
> >
> One of the situation of CcProbe used is in BaseIoLib.
> https://github.com/tianocore/edk2/blob/master/MdePkg/Library/BaseIoLibIntrinsic/IoLibInternalTdx.c#L35-L40
> 
> BaseIoLib is a basic library and it may be called by APs. While dynamic PCD access is not allowed in APs. Of course we can cache the PCD in a variable but I think it is still not safe.
> 
> Reserving the OVMF work area as RT_DATA breaks the original intention of the design.
> 
> Then how about this solution?
> https://edk2.groups.io/g/devel/message/91132
> We can design 2 instances of CcProbe. One is to read the OvmfWorkArea. The other is to call Cc guest specific way to determine the type.

When using RT_DATA is out of question there is no way around two
instances I think.

I don't see the point in reinventing the wheel though.  We know what the
guest type is, why determine it *again*?  We only need to copy the guest
type from the work area to another place before it is gone.  I think
the dxe library instance could copy it to a variable in the init function.

take care,
  Gerd