Eugene, HOBs and SMM are both part of the PI Specifications. From an implementation perspective, HOBs used in entry points of SMM core and SMM drivers can provide important platform/CPU state information. So I think use of HOBs from SMM modules is allowed.
You do bring up some good points, and I do agree that it is possible to define library abstractions that can be used to increase compatibility of EDK II modules. Mike > -----Original Message----- > From: edk2-devel [mailto:edk2-devel-boun...@lists.01.org] On Behalf Of Cohen, > Eugene > Sent: Wednesday, February 3, 2016 8:23 AM > To: edk2-devel@lists.01.org; Kinney, Michael D <michael.d.kin...@intel.com>; > Fan, Jeff > <jeff....@intel.com> > Subject: [edk2] MdePkg/SmmMemLib: Insufficient abstraction for CPU physical > address > size > > In SmmMemLib there's a routine to determine the maximum physical address > supported by a > processor: > > > // > // Get physical address bits supported. > // > Hob = GetFirstHob (EFI_HOB_TYPE_CPU); > if (Hob != NULL) { > PhysicalAddressBits = ((EFI_HOB_CPU *) Hob)->SizeOfMemorySpace; > } else { > AsmCpuid (0x80000000, &RegEax, NULL, NULL, NULL); > if (RegEax >= 0x80000008) { > AsmCpuid (0x80000008, &RegEax, NULL, NULL, NULL); > PhysicalAddressBits = (UINT8) RegEax; > } else { > PhysicalAddressBits = 36; > } > > } > > > > This is problematic in a couple ways: > > > > 1. AsmCpuid is not portable across architectures (understandably we would > have said > that SMM is an IA thing originally) > > 2. The PI spec for SMM does not specify the use of HOBs (in fact I was very > surprised > to even see HOBs in SMM, and even more confounded by platforms using the > "DxeHobLib" in > the SMM core and drivers!) > > > > I think this would be a good job for a base library interface to handle - > (e.g. UINTN > GetCpuPhysicalAddressBits(). You could then have a version that uses HOBs > (MdePkg), > another IA specific one (UefiCpuPackage) that uses CPU ID, and one that works > for ARM > (ArmPkg) that reads ID registers. > > > > Does that sound reasonable? > > > > [Presumably this is just the beginning - we see AsmCpuId show up in a lot of > modules > that need to be architecture-agnostic like BootScript (1G page support), > CapsulePei (1G > page support), and AcpiS3SaveDxe (1G pages and physical address size).] > > > > Eugene > _______________________________________________ > edk2-devel mailing list > edk2-devel@lists.01.org > https://lists.01.org/mailman/listinfo/edk2-devel _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel
