Re: [edk2-devel] [PATCH v3 1/1] MdeModulePkg: Add the EFI_RESOURCE_ATTRIBUTE_SPECIAL_PURPOSE attribute

["Oliver Smith-Denny" <osde@linux.microsoft.com>]

On 5/23/2024 2:17 AM, Du Lin wrote:
> Thanks for the quick response.
> 
> Agree that the PI and UEFI specs are vague on SP. That is also why I opted to minimize code changes to DXE core for SP support in patch https://edk2.groups.io/g/devel/message/118712.
> 
> Would it make more sense to let the caller determine if SP memory is available for UEFI via EFI resource types (e.g., EFI_RESOURCE_SYSTEM_MEMORY vs EFI_RESOURCE_MEMORY_RESERVED)?
> 
> CDAT can be read in PEI phase via DOE method and CDAT is important to support CXL 2.0. I believe CDAT spec is referencing EFI_MEMORY_TYPE and Memory Attributes defined in UEFI spec section 7.2. "EfiConventionalMemory Type with EFI_MEMORY_SP Attribute" may suggest that the memory type shall be EfiConventionalMemory and the attribute shall have SP set when reporting the memory to OS. And the concern is whether this combination can still be supported if we always mark resource HOBs with SP set as EfiGcdMemoryTypeReserved.

Thanks for the clarification. I agree that it makes sense to let the
resource HOB creator determine whether UEFI will put this in
system memory or reserved memory. DxeCore at that point could decide
to not allocate any memory with the EFI_MEMORY_SP attribute (or it
could decide it doesn't care).

We are meeting with some CXL stakeholders to make sure there is no
concern with changing this patch and then we will respin this.

Thanks,
Oliver


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