Message-ID: <BN9PR11MB5483E191F1906641565A1337E694A@BN9PR11MB5483.namprd11.prod.outlook.com>
Date: Fri, 22 Dec 2023 19:52:37 +0000
From: "Chiu, Chasel" <chasel.chiu@...el.com>
To: Ard Biesheuvel <ardb@...nel.org>
CC: Simon Glass <sjg@...omium.org>, "devicetree@...r.kernel.org"
	<devicetree@...r.kernel.org>, Mark Rutland <mark.rutland@....com>, "Rob
 Herring" <robh@...nel.org>, "Tan, Lean Sheng" <sheng.tan@...ements.com>, lkml
	<linux-kernel@...r.kernel.org>, Dhaval Sharma <dhaval@...osinc.com>, "Brune,
 Maximilian" <maximilian.brune@...ements.com>, Yunhui Cui
	<cuiyunhui@...edance.com>, "Dong, Guo" <guo.dong@...el.com>, Tom Rini
	<trini@...sulko.com>, ron minnich <rminnich@...il.com>, "Guo, Gua"
	<gua.guo@...el.com>, "linux-acpi@...r.kernel.org"
	<linux-acpi@...r.kernel.org>, U-Boot Mailing List <u-boot@...ts.denx.de>
Subject: RE: [PATCH v7 2/2] schemas: Add some common reserved-memory usages


Please see my reply below inline.

Thanks,
Chasel


> -----Original Message-----
> From: Ard Biesheuvel <ardb@...nel.org>
> Sent: Friday, December 22, 2023 4:48 AM
> To: Chiu, Chasel <chasel.chiu@...el.com>
> Cc: Simon Glass <sjg@...omium.org>; devicetree@...r.kernel.org; Mark Rutland
> <mark.rutland@....com>; Rob Herring <robh@...nel.org>; Tan, Lean Sheng
> <sheng.tan@...ements.com>; lkml <linux-kernel@...r.kernel.org>; Dhaval
> Sharma <dhaval@...osinc.com>; Brune, Maximilian
> <maximilian.brune@...ements.com>; Yunhui Cui <cuiyunhui@...edance.com>;
> Dong, Guo <guo.dong@...el.com>; Tom Rini <trini@...sulko.com>; ron minnich
> <rminnich@...il.com>; Guo, Gua <gua.guo@...el.com>; linux-
> acpi@...r.kernel.org; U-Boot Mailing List <u-boot@...ts.denx.de>
> Subject: Re: [PATCH v7 2/2] schemas: Add some common reserved-memory
> usages
> 
> On Thu, 21 Dec 2023 at 17:50, Chiu, Chasel <chasel.chiu@...el.com> wrote:
> >
> >
> > Hi Ard,
> >
> > Please see my reply below inline and let me know your thoughts.
> >
> > Thanks,
> > Chasel
> >
> >
> > > -----Original Message-----
> > > From: Ard Biesheuvel <ardb@...nel.org>
> > > Sent: Thursday, December 21, 2023 6:31 AM
> > > To: Chiu, Chasel <chasel.chiu@...el.com>
> > > Cc: Simon Glass <sjg@...omium.org>; devicetree@...r.kernel.org; Mark
> > > Rutland <mark.rutland@....com>; Rob Herring <robh@...nel.org>; Tan,
> > > Lean Sheng <sheng.tan@...ements.com>; lkml
> > > <linux-kernel@...r.kernel.org>; Dhaval Sharma <dhaval@...osinc.com>;
> > > Brune, Maximilian <maximilian.brune@...ements.com>; Yunhui Cui
> > > <cuiyunhui@...edance.com>; Dong, Guo <guo.dong@...el.com>; Tom Rini
> > > <trini@...sulko.com>; ron minnich <rminnich@...il.com>; Guo, Gua
> > > <gua.guo@...el.com>; linux- acpi@...r.kernel.org; U-Boot Mailing
> > > List <u-boot@...ts.denx.de>
> > > Subject: Re: [PATCH v7 2/2] schemas: Add some common reserved-memory
> > > usages
> > >
> > > On Tue, 28 Nov 2023 at 21:31, Chiu, Chasel <chasel.chiu@...el.com> wrote:
> > > >
> > > >
> > > >
> > > >
> > > > > -----Original Message-----
> > > > > From: Ard Biesheuvel <ardb@...nel.org>
> > > > > Sent: Tuesday, November 28, 2023 10:08 AM
> > > > > To: Chiu, Chasel <chasel.chiu@...el.com>
> > > > > Cc: Simon Glass <sjg@...omium.org>; devicetree@...r.kernel.org;
> > > > > Mark Rutland <mark.rutland@....com>; Rob Herring
> > > > > <robh@...nel.org>; Tan, Lean Sheng <sheng.tan@...ements.com>;
> > > > > lkml <linux-kernel@...r.kernel.org>; Dhaval Sharma
> > > > > <dhaval@...osinc.com>; Brune, Maximilian
> > > > > <maximilian.brune@...ements.com>; Yunhui Cui
> > > > > <cuiyunhui@...edance.com>; Dong, Guo <guo.dong@...el.com>; Tom
> > > > > Rini <trini@...sulko.com>; ron minnich <rminnich@...il.com>;
> > > > > Guo, Gua <gua.guo@...el.com>; linux- acpi@...r.kernel.org;
> > > > > U-Boot Mailing List <u-boot@...ts.denx.de>
> > > > > Subject: Re: [PATCH v7 2/2] schemas: Add some common
> > > > > reserved-memory usages
> > > > >
> > > > > You are referring to a 2000 line patch so it is not 100% clear where to look
> tbh.
> > > > >
> > > > >
> > > > > On Tue, 21 Nov 2023 at 19:37, Chiu, Chasel <chasel.chiu@...el.com>
> wrote:
> > > > > >
> > > > > >
> > > > > > In PR, UefiPayloadPkg/Library/FdtParserLib/FdtParserLib.c,
> > > > > > line
> > > > > > 268 is for
> > > > > related example code.
> > > > > >
> > > > >
> > > > > That refers to a 'memory-allocation' node, right? How does that
> > > > > relate to the 'reserved-memory' node?
> > > > >
> > > > > And crucially, how does this clarify in which way "runtime-code"
> > > > > and
> > > > > "runtime- data" reservations are being used?
> > > > >
> > > > > Since the very beginning of this discussion, I have been asking
> > > > > repeatedly for examples that describe the wider context in which
> > > > > these
> > > reservations are used.
> > > > > The "runtime" into runtime-code and runtime-data means that
> > > > > these regions have a special significance to the operating
> > > > > system, not just to the next bootloader stage. So I want to
> > > > > understand exactly why it is necessary to describe these regions
> > > > > in a way where the operating system might be expected to
> > > > > interpret this information and act
> > > upon it.
> > > > >
> > > >
> > > >
> > > > I think runtime code and data today are mainly for supporting UEFI
> > > > runtime
> > > services - some BIOS functions for OS to utilize, OS may follow
> > > below ACPI spec to treat them as reserved range:
> > > > https://uefi.org/specs/ACPI/6.5/15_System_Address_Map_Interfaces.h
> > > > tml# uefi-memory-types-and-mapping-to-acpi-address-range-types
> > > >
> > > > Like I mentioned earlier, that PR is still in early phase and has
> > > > not reflected all
> > > the required changes yet, but the idea is to build
> > > gEfiMemoryTypeInformationGuid HOB from FDT reserved-memory nodes.
> > > > UEFI generic Payload has DxeMain integrated, however Memory Types
> > > > are
> > > platform-specific, for example, some platforms may need bigger
> > > runtime memory for their implementation, that's why we want such FDT
> > > reserved-memory node to tell DxeMain.
> > > >
> > >
> > > > The Payload flow will be like this:
> > > >   Payload creates built-in default MemoryTypes table ->
> > > >     FDT reserved-memory node to override if required (this also
> > > > ensures the
> > > same memory map cross boots so ACPI S4 works) ->
> > > >       Build gEfiMemoryTypeInformationGuid HOB by "platfom specific"
> > > MemoryTypes Table ->
> > > >         DxeMain/GCD to consume this MemoryTypes table and setup
> > > > memory
> > > service ->
> > > >           Install memory types table to UEFI system table.Configuration table...
> > > >
> > > > Note: if Payload built-in default MemoryTypes table works fine for
> > > > the platform, then FDT reserved-memory node does not need to
> > > > provide such
> > > 'usage' compatible strings. (optional) This FDT node could allow
> > > flexibility/compatibility without rebuilding Payload binary.
> > > >
> > > > Not sure if I answered all your questions, please highlight which
> > > > area you need
> > > more information.
> > > >
> > >
> > > 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?
> >
> >
> > 1. 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-create gEfiMemoryTypeInformationGuid HOB basing
> on FDT input (instead of the default MemoryType inside UefiPayload) ->
> >       UefiPayload DxeMain/Gcd will consume gEfiMemoryTypeInformationGuid
> Hob for memory type information ->
> >         UefiPayload to initialize UEFI environment (mainly DXE dispatcher) ->
> >           (additional FV binary appended to common UefiPayload binary)
> PlatformPayload to provide VariableService which is platform specific ->
> >             UefiPayload UefiBootManager will SetVariable if memory 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.


> 
> >
> > 2. 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.
> >
> >       - acpi
> > If 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-nvs
> > If PlatformInit has created some ACPI tables which having ACPI NVS memory
> dependency, this will be that nvs region.
> >
> 
> These make sense.
> 
> >       - boot-code
> > When PlatformInit having some FW boot phase code that could be freed
> > for OS to use when payload transferring control to UEFI OS
> >
> >       - boot-data
> > When PlatformInit having some FW boot phase data that could be freed for OS
> to use when payload transferring control to UEFI OS.
> >
> >       - runtime-code
> > PlatformInit may provide some services code that can be used for Payload to
> initialize UEFI Runtime Services for supporting UEFI OS.
> >
> >       - runtime-data
> > PlatformInit 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#efi-boot-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.

Would you provide a real OS case which will be impacted by this reserved-memory schema so we can discuss basing on real case?

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