Yes please! Thanks, Ray > -----Original Message----- > From: Nhi Pham <n...@os.amperecomputing.com> > Sent: Thursday, November 30, 2023 9:59 PM > To: Oliver Smith-Denny <o...@linux.microsoft.com>; devel@edk2.groups.io; > a...@kernel.org > Cc: Ni, Ray <ray...@intel.com>; huangm...@linux.alibaba.com; Sami Mujawar > <sami.muja...@arm.com>; Ard Biesheuvel <ardb+tianoc...@kernel.org>; > Yao, Jiewen <jiewen....@intel.com>; Supreeth Venkatesh > <supreeth.venkat...@arm.com>; ming.hua...@outlook.com > Subject: Re: [edk2-devel] [PATCH v1 2/2] StandaloneMmPkg: Fix HOB space > and heap space conflicted issue > > 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
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