Re: [edk2-devel] [PATCH v1 2/2] StandaloneMmPkg: Fix HOB space and heap space conflicted issue

["Ni, Ray" <ray.ni@intel.com>]

Yes please!

Thanks,
Ray
> -----Original Message-----
> From: Nhi Pham <nhi@os.amperecomputing.com>
> Sent: Thursday, November 30, 2023 9:59 PM
> To: Oliver Smith-Denny <osde@linux.microsoft.com>; devel@edk2.groups.io;
> ardb@kernel.org
> Cc: Ni, Ray <ray.ni@intel.com>; huangming@linux.alibaba.com; Sami Mujawar
> <sami.mujawar@arm.com>; Ard Biesheuvel <ardb+tianocore@kernel.org>;
> Yao, Jiewen <jiewen.yao@intel.com>; Supreeth Venkatesh
> <supreeth.venkatesh@arm.com>; ming.huang-@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
> >>> <nhi@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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