-----Original Message----- From: Ard Biesheuvel ardb@kernel.org Sent: Thursday, January 4, 2024 12:43 AM To: Chiu, Chasel chasel.chiu@intel.com Cc: Simon Glass sjg@chromium.org; devicetree@vger.kernel.org; Mark Rutland mark.rutland@arm.com; Rob Herring robh@kernel.org; Tan, Lean Sheng sheng.tan@9elements.com; lkml linux-kernel@vger.kernel.org; Dhaval Sharma dhaval@rivosinc.com; Brune, Maximilian maximilian.brune@9elements.com; Yunhui Cui cuiyunhui@bytedance.com; Dong, Guo guo.dong@intel.com; Tom Rini trini@konsulko.com; ron minnich rminnich@gmail.com; Guo, Gua gua.guo@intel.com; linux- acpi@vger.kernel.org; U-Boot Mailing List u-boot@lists.denx.de Subject: Re: [PATCH v7 2/2] schemas: Add some common reserved-memory usages
On Thu, 4 Jan 2024 at 01:25, Chiu, Chasel chasel.chiu@intel.com wrote:
-----Original Message----- From: Ard Biesheuvel ardb@kernel.org Sent: Wednesday, January 3, 2024 7:22 AM To: Chiu, Chasel chasel.chiu@intel.com Cc: Simon Glass sjg@chromium.org; devicetree@vger.kernel.org; Mark Rutland mark.rutland@arm.com; Rob Herring robh@kernel.org; Tan, Lean Sheng sheng.tan@9elements.com; lkml linux-kernel@vger.kernel.org; Dhaval Sharma dhaval@rivosinc.com; Brune, Maximilian maximilian.brune@9elements.com; Yunhui Cui cuiyunhui@bytedance.com; Dong, Guo guo.dong@intel.com; Tom Rini trini@konsulko.com; ron minnich rminnich@gmail.com; Guo, Gua gua.guo@intel.com; linux- acpi@vger.kernel.org; U-Boot Mailing List u-boot@lists.denx.de Subject: Re: [PATCH v7 2/2] schemas: Add some common reserved-memory usages
On Fri, 22 Dec 2023 at 20:52, Chiu, Chasel chasel.chiu@intel.com wrote:
Please see my reply below inline.
Thanks, Chasel
...
> The gEfiMemoryTypeInformationGuid HOB typically carries > platform defaults, and the actual memory type information is > kept in a non-volatile EFI variable, which gets updated when > the memory usage changes. Is this different for UefiPayloadPkg? > > (For those among the cc'ees less versed in EFI/EDK2: when > you get the 'config changed -rebooting' message from the > boot firmware, it typically means that this memory type > table has changed, and a reboot is necessary.) > > So the platform init needs to read this variable, or get the > information in a different way. I assume it is the payload, > not the platform init that updates the variable when > necessary. This means the information flows from payload(n) > to platform init(n+1), where n is a monotonic index tracking > consecutive boots of the
system.
> > Can you explain how the DT fits into this? How are the > runtime-code and runtime-data memory reservation nodes under > /reserved-memory used to implement this information exchange > between platform init and payload? And how do the HOB and > the EFI
variable fit into this picture?
- With some offline discussion, we would move
gEfiMemoryTypeInformationGuid usage to FDT->upl-custom node. This is because it is edk2 implementation choice and non-edk2 PlatformInit or Payload may not have such memory optimization implementation. (not a generic usage/requirement for PlatformInit and Payload)
The edk2 example flow will be like below:
PlatformInit to GetVariable of gEfiMemoryTypeInformationGuid and create Hob-
PlatformInit to initialize FDT->upl-custom node to report
gEfiMemoryTypeInformationGuid HOB information ->
UefiPayload entry to re-creategEfiMemoryTypeInformationGuid HOB basing
on FDT input (instead of the default MemoryType inside UefiPayload) ->
UefiPayload DxeMain/Gcd will consumegEfiMemoryTypeInformationGuid
Hob for memory type information ->
UefiPayload to initialize UEFI environment (mainly DXE dispatcher) -(additional FV binary appended to common UefiPayloadbinary)
PlatformPayload to provide VariableService which is platform specific ->
UefiPayload UefiBootManager will SetVariable ifmemory type change
needed and request a warm reset ->
Back to PlatformInit ...OK so the upl-custom node can do whatever it needs to. I imagine these will include the memory descriptor attribute field, and other parts that may be missing from the /reserved-memory DT node
specification?
Yes, if needed by edk2 specific implementation, not generic enough, we may
consider to use upl-custom node to pass those data.
- Now the proposed reserved-memory node usages will be for
PlatformInit to
provide data which may be used by Payload or OS. This is not edk2 specific and any PlatformInit/Payload could have same support.
Note: all of below are optional and PlatformInit may choose to implement some
of them or not.
- acpiIf PlatformInit created some ACPI tables, this will report a memory region which
contains all the tables to Payload and Payload may base on this to add some more tables if required.
- acpi-nvsIf PlatformInit has created some ACPI tables which having ACPI NVS memory
dependency, this will be that nvs region.
These make sense.
- boot-codeWhen PlatformInit having some FW boot phase code that could be freed for OS to use when payload transferring control to UEFI OS
- boot-dataWhen PlatformInit having some FW boot phase data that could be freed for OS
to use when payload transferring control to UEFI OS.
- runtime-codePlatformInit may provide some services code that can be used for Payload to
initialize UEFI Runtime Services for supporting UEFI OS.
- runtime-dataPlatformInit may provide some services data that can be used for Payload to
Initialize UEFI Runtime Services for supporting UEFI OS.
A UEFI OS must consume this information from the UEFI memory map, not from the /reserved-memory nodes. So these nodes must either not be visible to the OS at all, or carry an annotation that the OS must ignore
them.
Would it be possible to include a restriction in the DT schema that these are only valid in the firmware boot phase?
https://uefi.org/specs/UEFI/2.10/07_Services_Boot_Services.html#ef i-bo ot-services-exitbootservices Per UEFI specification, UEFI OS will always call UEFI GetMemoryMap function to retrieve memory map, so FDT
node present or not does not matter to UEFI OS. We probably could have annotation in UPL specification to emphasize this.
I'm not familiar with Linux FDT boot, but if non-UEFI OS does not call UEFI
GetMemoryMap() and does not know what is runtime-code/data, boot- code/data, it might just treat such reserved-memory nodes as 'regular' reserved memory nodes, and that's still ok because non-UEFI OS will not call to any runtime service or re-purpose boot-code/data
memory regions.
You are saying the same thing but in a different way. A UEFI OS must only rely on GetMemoryMap(), and not on the /reserved-memory node to obtain this information. But this requirement needs to be stated somewhere: the UEFI spec does not reason about other sources of EFI memory information at all, and this DT schema does not mention any of this
either.
Would you provide a real OS case which will be impacted by this reserved-
memory schema so we can discuss basing on real case?
Funny, that is what I have been trying to get from you :-)
The problem I am anticipating here is that the information in /reserved-memory may be out of sync with the EFI memory map. It needs to be made clear that the EFI memory map is the only source of truth when the OS is involved, and this /reserved-memory mechanism should only be used by other firmware stages. But the schema does not mention this at all. The schema also does not mention that the information in /reserved-memory is not actually sufficient to reconstruct the EFI memory map that the firmware payload expects (which is why the upl- custom-node exists too)
Does below solve your concerns if we mention those in schema description? (please feel free to add more if you have) . boot-code/boot-data
and runtime-code/runtime-data usages are following UEFI specification
. before ExitBootServices:
https://uefi.org/specs/UEFI/2.10/07_Services_Boot_Services.html#memory- type-usage-before-exitbootservices
. after ExitBootServices: https://uefi.org/specs/UEFI/2.10/07_Services_Boot_Services.html#memory -type-usage-after-exitbootservices . These usages do not intend to construct full UEFI memory map, it is only for
PlatformInit to pass pre-installed tables or services to Payload for supporting UEFI OS boot.
. These usages are optional . Typically UEFI OS boot will always call GetMemoryMap() to retrieve memory map following UEFI spec, no matter DT nodes present or not (https://uefi.org/specs/UEFI/2.10/07_Services_Boot_Services.html#efi-b oot-services-exitbootservices) . Typically Non-UEFI OS boot will treat those boot* or runtime* reserved-memory as 'regular' reserved memory if
present.
This already helps quite a lot, thanks.
But why should a non-UEFI OS be required to keep boot* or runtime* regions reserved? The firmware stage that boots the OS knows whether it is performing an UEFI boot or a non-UEFI boot, and it should only present the information that goes along with that. The OS should never have to worry about reconciling two sources of truth.
And to Rob's point about boot / runtime being ill-defined: I would argue that 'runtime' quite clearly implies 'under the OS', and so UEFI runtime* reservations are assumed to always be relevant to UEFI OSes.
I think there is a fundamental difference of opinion here, where the position of the firmware developers is that the DT should be the same across all boot stages, while my position reasoning from the OS side is that the OS should be able to observe only the abstractions that are part of the contract between firmware and OS.
I agree that boot* and runtime* can be utilized by non-UEFI OS too, we are just reusing existing definitions from UEFI spec. . boot-code/boot-data: firmware stage code/data that can be freed after firmware stage ending so OS will have more usable memory. . runtime-code/runtime-data: firmware stage code/data that are intended to be utilized by OS stage. Non-UEFI OS still can implement/support boot* or runtime* memory if they want, and the runtime service can be 'non-UEFI' runtime service too as long as OS/FW aligning each other. Or non-UEFI OS can simply treat them as "usable memory" if they do not call to any runtime services from those memory regions. (in this case runtime* memory can be repurposed just like boot* memory) That will be OS choices and we may add some example OS handling to schema description too.
While we are working on UPL specific DT, we got agreement that 2 separate DT are unnecessary, we better align/merge with existing OS DT and OS could utilize those additional UPL DT information too if they want. This also simplifies/unifies PlatformInit as same DT could support different OS loader Payloads.