On 9/7/2023 10:38 PM, Nhi Pham wrote: > On 9/6/2023 11:22 PM, Oliver Smith-Denny wrote: >> On 9/6/2023 1:50 AM, Ard Biesheuvel wrote: >>> On Wed, 6 Sept 2023 at 09:56, Nhi Pham >>> <n...@amperemail.onmicrosoft.com> wrote: >>>> >>>> On 9/6/2023 1:33 PM, Ni, Ray wrote: >>>>> [EXTERNAL EMAIL NOTICE: This email originated from an external sender. >>>>> Please be mindful of safe email handling and proprietary information >>>>> protection practices.] >>>>> >>>>> I am a bit confused. >>>>> >>>>> The HOB list in standalone MM is read-only. Why could any module call >>>>> BuildGuidHob() to modify the HOB. >>>>> >>>>> I saw Oliver mentioned something about StMM. I don't know what that >>>>> is. >>>>> But it seems that's ARM specific. Then, I don't think it's proper to >>>>> modify code here for a specific arch ARM. >>>> >>>> The HOB creation is available in the >>>> StandaloneMmPkg/Library/StandaloneMmHobLib/StandaloneMmHobLib.inf. If >>>> other architectures also use that instance, I think the issue is not >>>> specific to ARM. >>>> >>> >>> The question here is whether the implementation follows the PI spec, >>> and whether HOB creation should be supported to begin with. >>> >> >> My reading of the PI spec is that this implementation does not follow >> it. However, the PI spec is not very explicit about Standalone MM in >> general, but particularly in relation to HOBs. >> >> However, in the generic HOB section of PI spec v1.7, Vol. 3, section 4 >> (entitled HOB Design Discussion) it explicitly lays out that there are >> HOB producer phases and HOB consumer phases. It uses PEI as a HOB >> producer phase and DXE as a HOB consumer phase and explicitly says >> that the HOB consumer phase must treat HOBs as read-only memory, per >> Ray's comment. >> >> In vol. 4, section 2.2, in discussing the Standalone MM entry point, >> the document talks about the HOB list being passed to Standalone MM >> to consume, which per the reading of the above section would classify >> Standalone MM as a HOB consumer phase, where HOBs should then be >> read-only. >> >> So, I believe that we should not support HOB creation in Standalone MM >> and instead rely on other mechanisms to pass information within the >> phase. Per Nhi's other email in this thread, we should have the >> discussion on how to solve that specific problem and that may well >> lead to a discussion on whether HOBs are in fact the right mechanism >> here, but I tend to lean towards leaving something as architectural as >> HOBs to what the PI spec defines and using different mechanisms to >> accomplish in-phase communication. > Thanks Oliver so much for that. I agree. We should focus on my specific > problem with UEFI Variable Flash Info in StandaloneMM in another thread. >> >> Does this reading of the spec align with others' expectations? As I >> mentioned to Ray in another thread, Standalone MM feels like it could >> have extra clarification in a few areas in the PI spec. > > Thanks again. The HOB library should be updated to remove the HOB > creation once we have the clarification.
I found that we can hook a platform NULL library class to the StandaloneMmCore to create UEFI Variable Flash Info HOB. This way is compliant to the spec as the HOB is created in MM_CORE_STANDALONE phase. Should I write a patch to remove the HOB creation in StandaloneMmHobLib? Regards, Nhi -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#111903): https://edk2.groups.io/g/devel/message/111903 Mute This Topic: https://groups.io/mt/89020085/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
