Message-ID: <CAPnjgZ2wOj4Ue2YEM860ubHj=Uzs+Xf7AfAoTFFeX13mRYW46g@mail.gmail.com>
Date:   Fri, 1 Sep 2023 05:54:55 -0600
From:   Simon Glass <sjg@...omium.org>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>, devicetree@...r.kernel.org,
        Rob Herring <robh@...nel.org>,
        Chiu Chasel <chasel.chiu@...el.com>,
        U-Boot Mailing List <u-boot@...ts.denx.de>,
        Gua Guo <gua.guo@...el.com>, linux-acpi@...r.kernel.org,
        lkml <linux-kernel@...r.kernel.org>,
        Yunhui Cui <cuiyunhui@...edance.com>,
        ron minnich <rminnich@...il.com>,
        Tom Rini <trini@...sulko.com>,
        Lean Sheng Tan <sheng.tan@...ements.com>
Subject: Re: [PATCH v3 1/2] schemas: Add a schema for memory map

Hi Ard,

On Fri, 1 Sept 2023 at 04:48, Ard Biesheuvel <ardb@...nel.org> wrote:
>
> On Fri, 1 Sept 2023 at 03:12, Simon Glass <sjg@...omium.org> wrote:
> >
> > Hi Ard,
> >
> > On Thu, 31 Aug 2023 at 16:39, Ard Biesheuvel <ardb@...nel.org> wrote:
> > >
> > > On Fri, 1 Sept 2023 at 00:17, Simon Glass <sjg@...omium.org> wrote:
> > > >
> > > > Hi Ard,
> > > >
> > > > On Thu, 31 Aug 2023 at 15:48, Ard Biesheuvel <ardb@...nel.org> wrote:
> > > > >
> > > > > On Thu, 31 Aug 2023 at 21:03, Simon Glass <sjg@...omium.org> wrote:
> > > > > >
> > > > > > Hi Ard,
> > > > > >
> > > > > > On Thu, 31 Aug 2023 at 06:28, Ard Biesheuvel <ardb@...nel.org> wrote:
> > > > > > >
> > > > > > > On Wed, 30 Aug 2023 at 23:11, Simon Glass <sjg@...omium.org> wrote:
> > > > > > > >
> > > > > > > > Hi Ard,
> > > > > > > >
> > > > > > > > On Tue, 29 Aug 2023 at 15:32, Ard Biesheuvel <ardb@...nel.org> wrote:
> > > > > > > > >
> > > > > > > > > On Tue, 29 Aug 2023 at 21:18, Simon Glass <sjg@...omium.org> wrote:
> > > > > > > > > >
> > > > > > > > > > Hi Ard,
> > > > > > > > > >
> > > > > > > > > > On Thu, 24 Aug 2023 at 03:10, Ard Biesheuvel <ardb@...nel.org> wrote:
> > > > > > > ...
> > > > > > > > > > > In summary, I don't see why a non-UEFI payload would care about UEFI
> > > > > > > > > > > semantics for pre-existing memory reservations, or vice versa. Note
> > > > > > > > > > > that EDK2 will manage its own memory map, and expose it via UEFI boot
> > > > > > > > > > > services and not via DT.
> > > > > > > > > >
> > > > > > > > > > Bear in mind that one or both sides of this interface may be UEFI.
> > > > > > > > > > There is no boot-services link between the two parts that I have
> > > > > > > > > > outlined.
> > > > > > > > > >
> > > > > > > > >
> > > > > > > > > I don't understand what this means.
> > > > > > > > >
> > > > > > > > > UEFI specifies how one component invokes another, and it is not based
> > > > > > > > > on a DT binding. If the second component calls UEFI boot or runtime
> > > > > > > > > services, it should be invoked in this manner. If it doesn't, then it
> > > > > > > > > doesn't care about these memory reservations (and the OS will not be
> > > > > > > > > booted via UEFI either)
> > > > > > > > >
> > > > > > > > > So I feel I am missing something here. Perhaps a practical example
> > > > > > > > > would be helpful?
> > > > > > > >
> > > > > > > > Let's say we want to support these combinations:
> > > > > > > >
> > > > > > > > Platform Init -> Payload
> > > > > > > > --------------------------------
> > > > > > > > U-Boot -> Tianocore
> > > > > > > > coreboot -> U-Boot
> > > > > > > > Tianocore -> U-Boot
> > > > > > > > Tianocore -> Tianocore
> > > > > > > > U-Boot -> U-Boot
> > > > > > > >
> > > > > > > > Some of the above things have UEFI interfaces, some don't. But in the
> > > > > > > > case of Tianocore -> Tianocore we want things to work as if it were
> > > > > > > > Tianocore -> (its own handoff mechanism) Tiancore.
> > > > > > > >
> > > > > > >
> > > > > > > If Tianocore is the payload, it is either implemented as a EFI app, in
> > > > > > > which case it has access to EFI services, or it is not, in which case
> > > > > > > it doesn't care about UEFI semantics of the existing reserved regions,
> > > > > > > and it only needs to know which regions exist and which of those are
> > > > > > > reserved.
> > > > > > >
> > > > > > > And I think the same applies to all other rows in your table: either
> > > > > > > the existence of UEFI needs to be carried forward, which needs to be
> > > > > > > done via EFI services, or it doesn't, in which case the UEFI specific
> > > > > > > reservations can be dropped, and only reserved and available memory is
> > > > > > > relevant.
> > > > > > >
> > > > > > > > Some Platform Init may create runtime code which needs to accessible later.
> > > > > > > >
> > > > > > >
> > > > > > > But not UEFI runtime code, right? If the payload is not UEFI based,
> > > > > > > the OS would never be able to call that runtime code unless it is
> > > > > > > described in a different, non-UEFI way. This is fine, but it is not
> > > > > > > UEFI so we shouldn't call it UEFI runtime memory.
> > > > > > >
> > > > > > > > The way I think of it is that we need to generalise the memory map a
> > > > > > > > bit. Saying that you must use UEFI boot services to discover it is too
> > > > > > > > UEFI-specific.
> > > > > > > >
> > > > > > >
> > > > > > > What I am questioning is why a memory map with UEFI semantics is even
> > > > > > > relevant when those boot services do not exist.
> > > > > > >
> > > > > > > Could you be more specific about why a payload would have to be aware
> > > > > > > of the existence of UEFI boot/runtime service regions if it does not
> > > > > > > consume the UEFI interfaces of the platform init? And if the payload
> > > > > > > exposes UEFI services to the OS, why would it consume a memory map
> > > > > > > with UEFI semantics rather than a simple list of memblocks and memory
> > > > > > > reservations?
> > > > > >
> > > > > > It seems like you are thinking of the Payload as grub, or something
> > > > > > like that? This is not about grub. If there are EFI boot services to
> > > > > > be provided, they are provided by the Payload, not Platform Init. I am
> > > > > > not that familiar with Tianocore, but if you are, perhaps think of it
> > > > > > as splitting Tianocore into two pieces, one of which inits the silicon
> > > > > > and the other which provides the EFI boot services.
> > > > > >
> > > > > > Again, if you are familiar with Tianocore, it can be built either as a
> > > > > > monolithic whole, or as a coreboot Payload. The Payload part of the
> > > > > > code is (roughly) the same in each case. But the Platform Init is
> > > > > > different[1]
> > > > > >
> > > > >
> > > > > I co-maintain OVMF [including the ARM port that I created from
> > > > > scratch] as well as the ARM architecture support in Tianocore, along
> > > > > with a couple of platform ports for ARM boards, some of which could by
> > > > > now be characterized as 'historical' (AMD Seattle, Socionext SynQuacer
> > > > > and Raspberry Pi 3/4). So I think I have a pretty good handle on how
> > > > > Tianocore based firmware is put together.
> > > > >
> > > > > Tianocore as a payload will expose boot services to the OS, and will
> > > > > provide the OS with a memory map using the UEFI APIs. But you still
> > > > > haven't explained why the memory description this Tianocore inherits
> > > > > from the Platform Init would include any UEFI boot or runtime service
> > > > > regions, or any of the other memory regions with UEFI semantics.
> > > > > TIanocore just needs to know a) where memory lives b) which parts of
> > > > > it are already in use (as far as the memory map is concerned), and the
> > > > > existing bindings suffice for this purpose.
> > > > >
> > > > > In short, the memory regions with UEFI semantics are created by the
> > > > > boot phase that actually exposes UEFI to the OS, in which case the
> > > > > boot services can be used to obtain the memory map. If the consumer is
> > > > > not UEFI based, there is no reason to bother it with descriptions of
> > > > > memory regions that have no significance to it.
> > > >
> > > > But aren't you assuming that the Payload knows how to handle the
> > > > hardware and can implement the runtime services? What if (for example)
> > > > powering off the device is hardware-specific and only Platform Init
> > > > knows how?
> > > >
> > >
> > > If the payload relies on the platform init for anything, it can use
> > > whichever interface those components manage to agree on.
> > >
> > > If this interface is UEFI, the payload can use UEFI to obtain the memory map.
> >
> > I think you are still getting mixed up with grub. Platform Init does
> > not necessarily provide EFI boot services, even for Tianocore. It is
> > the Payload which provides those services. In other words, the second
> > half of Tianocore does not use EFI boot services to talk to the first
> > half.
> >
>
> I might be misunderstanding your examples, as they are somewhat vague
> and hypothetical.
>
> Drawing from my experience working on Tianocore, allow me to give a
> few examples myself:
> - ArmVirtQemu (ARM port of OVMF) receives information about system RAM
> via memory nodes in the device tree, using device_type=memory, from
> QEMU, which fulfills the role of platform init in this case.
> ArmVirtQemu currently doesn't consume the /reserved-memory node as
> QEMU does not populate it, but that would be the appropriate place to
> document RAM regions that Tianocore must treat as reserved;
> - DeveloperBox [0] (based on Socionext SynQuacer) receives a platform
> specific struct with memory regions and reservations in a patch of
> SRAM that the early Tianocore code uses for stack and heap. Note that
> system RAM is not available yet at this point (as it is being
> discovered via this mechanism) and SRAM is quite tight, so DT is not
> an option here;
> - The Tianocore port for Raspberry Pi 4 [1] receives RAM information
> from the VideoCore firmware by calling the mailbox interface. This
> covers both available memory and reserved memory (for the GPU). The
> statically allocated TF-A code and data regions that reside in
> non-secure DRAM on this platform are reserved implicitly due to the
> fact that they are part of the same firmware image, which knows not to
> step on itself.
>
> In none of these cases, I see a need for the binding that you propose.
> Platfom Init -> Payload handover is highly platform specific, so
> adding another generic DT binding for an as yet unidentified use case
> seems seems premature at the very least.

I am working with the Tiancocore people and volunteered to submit this
binding on their behalf. I did try suggesting it was not needed, but
it seems that it is.

>
> [0] https://github.com/tianocore/edk2-platforms/tree/master/Platform/Socionext/DeveloperBox
> [1] https://github.com/tianocore/edk2-platforms/tree/master/Platform/RaspberryPi/RPi4
>
> > >
> > > If this interface is not UEFI, the UEFI memory map is irrelevant, and
> > > existing DT bindings are available that can describe this information.
> >
> > Can you please point me to those?
> >
>
> The /memory node is documented in the DT specification. The
> /reserved-memory node is documented here:
>
> Documentation/devicetree/bindings/reserved-memory/reserved-memory.yaml

OK, so I think we have reached a conclusion here.

>
> > >
> > > > On another track, would it help if we just dropped all mention of
> > > > UEFI? The binding does not mention it.
> > > >
> > >
> > > Your binding has
> > >
> > > +      usage:
> > > +        $ref: /schemas/types.yaml#/definitions/string
> > > +        description: |
> > > +          Describes the usage of the memory region, e.g.:
> > > +
> > > +            "acpi-reclaim", "acpi-nvs", "bootcode", "bootdata", "bootdata",
> > > +            "runtime-code", "runtime-data".
> > > +
> > > +            See enum EFI_MEMORY_TYPE in "Unified Extensible Firmware Interface
> > > +            (UEFI) Specification" for all the types. For now there are not
> > > +            listed here.
> > >
> > > Every type listed is derived from a definition in the UEFI spec, which
> > > is specifically mentioned as the source.
> >
> > Yes, but please see the v4 or v5 patch version, where that has
> > changed. I sent v4 two days ago. I am worried that you are still
> > responding to something that I revised in response to your original
> > comments?
> >
>
> No, I haven't looked at those yet. Maybe the uboot community is
> different, but in the Linux community, we tend to finish discussing vN
> of a series before sendindg out vN+1. This prevents the kind of
> parallel track discussions that seem to be taking place here. Also, it
> is highly appreciated when an author takes all feedback into account
> (or at least acknowledges it) in a vN+1 submission, which is difficult
> to do before the discussion around vN has concluded.

OK. I tend to react to feedback and try to rework my patches accordingly.

>
> ...
> > >
> > > But if the Platform Init wants to reserve some system RAM for runtime
> > > code (e.g., for its PSCI implementation on ARM), it can add it to the
> > > /reserved-memory node, where both the payload and the OS will be able
> > > to find it if needed.
> >
> > OK good. So with my binding that would be 'runtime-code@...'. I am
> > still not sure what the problem is here.
> >
>
> The problem is that you are not using /reserved-memory to describe a
> memory reservation but something new that all DT consumers need to be
> taught about, or they might step on memory that turns out to be
> reserved. The DT ecosystem is large and heterogeneous, and any tool or
> boot stage in existence is at the risk of stepping on this memory
> inadvertently, whereas /reserved-memory already provides the means to
> reserve it and document its nature.
>
> > >
> > > > I'm just not sure that Platform Init and Payload are as completely
> > > > independent as you seem to be suggesting. Once we get into the
> > > > Payload, the only things we know are what Platform Init told us.
> > > >
> > >
> > > They are not independent, and that is not at all what I am claiming.
> > >
> > > What I am objecting to is framing the platform init<->payload memory
> > > handover in terms of UEFI memory types, which may conflict with well
> > > established DT bindings that already serve the same purpose. The only
> > > difference between /reserved-memory and this binding seems to be the
> > > collection of UEFI memory types, which don't belong there in the first
> > > place.
> >
> > OK, so please help me get this resolved.
> >
>
> I have already indicated how this should be resolved in my opinion,
> which is by using the /reserved-memory node to describe memory
> reservations, and not this binding.

OK, that is the direction I took from Rob's email a week ago. Let's
continue any discussion on the v5 series.

Regards,
Simon

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