On 9/6/2023 4:29 AM, Oliver Smith-Denny wrote:
On 9/4/2023 7:20 PM, Nhi Pham wrote:
On 9/2/2023 3:43 AM, Oliver Smith-Denny wrote:
On 8/31/2023 1:20 AM, Nhi Pham via groups.io wrote:
If I am understanding this correctly, this is only an issue when
HOBs are created in StMM, i.e. not from HOBs that are passed in. Is
this
correct?
Yes, the issue only occurs when HOB are created in StandaloneMM by
the HOB library instance
StandaloneMmPkg/Library/StandaloneMmHobLib/StandaloneMmHobLib.inf
If so, is HOB creation in StMM and supported use case? The only
instance
I think it is intended to work as the CreateHob() function is
implemented.
Well, that may just be a copy/paste sort of thing :).
a quick search turns up is the ARM StMM Core entry, where some
information from TF-A is converted to HOB format. Do we have any other
use cases (and curious more on this use case). My thought process would
be that StMM would not create any HOBs. Depending on FW configuration,
it may receive HOBs from PEI.
I have a use case when enabling the UEFI Variable driver running in
StandaloneMM. Instead of using the PCDs, the in-memory NVRAM region
is allocated **dynamically** at boot time in the StMM secure memory.
Then, they will be passed into the gVariableFlashInfoHobGuid for
being consumed by other variable MM drivers.
I do believe that per the PI spec, we should have HOB producer and HOB
consumer phases, where in this case PEI (if it was the launching entity
for StMM) is the HOB producer and StMM is the HOB producer. This is the
same pattern the PI spec details for PEI and DXE, where DXE is not
intended to create new HOBs, but just to consume information from the
previous phase.
As I mentioned, there are other interfaces for passing information
within a phase, such as protocols, dynamic PCDs, variables, etc. that
are built for this application. I think it is useful to adhere to the
model for HOBs (which are hand off blocks, one phase handing information
to another phase) and that we will create more issues if we rely on
HOB consumer phases producing HOBs.
Thanks Oliver for the explanation. That makes sense to me.
My proposal would be to remove the HOB creation code from StMM
completely. I believe in your use case that you are describing a dynamic
PCD or a protocol could work to pass the information.
I think the dynamic PCD is supposed to not being supported in
StandaloneMM and protocol does not fit because the Variable Flash Info
is created in PEI for UEFI variable non-MM flow and in StMM for UEFI
variable MM flow.
If we are saying that prior to your patch that HOB creation in StMM was
completely broken, anyway, it seems that folks were not relying on this
code?
Right, it is just my curiosity that I don't see any showcase for
Variable MM + Variable Flash Info HOB in StandaloneMM.
Adding Michael Kubacki as the owner of the Variable Flash Info HOB for
getting further input.
Thanks,
Oliver
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