[PATCH v4 14/35] efi_loader: Allocate and write ACPI tables

Ilias Apalodimas ilias.apalodimas at linaro.org
Fri Sep 27 13:30:03 CEST 2024 

On Fri, 27 Sept 2024 at 13:53, Simon Glass <sjg at chromium.org> wrote:
>
> Hi Ilias,
>
> On Thu, 26 Sept 2024 at 13:18, Ilias Apalodimas
> <ilias.apalodimas at linaro.org> wrote:
> >
> > On Thu, 26 Sept 2024 at 14:04, Simon Glass <sjg at chromium.org> wrote:
> > >
> > > Hi Patrick,
> > >
> > > On Thu, 26 Sept 2024 at 10:01, Patrick Rudolph
> > > <patrick.rudolph at 9elements.com> wrote:
> > > >
> > > > Hi Simon,
> > > > On Fri, Sep 20, 2024 at 6:01 PM Simon Glass <sjg at chromium.org> wrote:
> > > > >
> > > > > Hi Ilias,
> > > > >
> > > > > On Fri, 20 Sept 2024 at 08:36, Ilias Apalodimas
> > > > > <ilias.apalodimas at linaro.org> wrote:
> > > > > >
> > > > > > Hi Simon,
> > > > > >
> > > > > > On Thu, 19 Sept 2024 at 18:36, Simon Glass <sjg at chromium.org> wrote:
> > > > > > >
> > > > > > > Hi Ilias,
> > > > > > >
> > > > > > > On Thu, 19 Sept 2024 at 17:20, Ilias Apalodimas
> > > > > > > <ilias.apalodimas at linaro.org> wrote:
> > > > > > > >
> > > > > > > > Hi Simon,
> > > > > > > >
> > > > > > > > On Thu, 19 Sept 2024 at 18:00, Simon Glass <sjg at chromium.org> wrote:
> > > > > > > > >
> > > > > > > > > Hi Ilias,
> > > > > > > > >
> > > > > > > >
> > > > > > > > [...]
> > > > > > > >
> > > > > > > > > > > > +
> > > > > > > > > > > > +               if (!addr)
> > > > > > > > > > > > +                       return log_msg_ret("mem", -ENOMEM);
> > > > > > > > > > > > +       } else {
> > > > > > > > > > > > +               pages = efi_size_in_pages(TABLE_SIZE);
> > > > > > > > > > > > +
> > > > > > > > > > > > +               ret = efi_allocate_pages(EFI_ALLOCATE_ANY_PAGES,
> > > > > > > > > > > > +                                        EFI_ACPI_RECLAIM_MEMORY,
> > > > > > > > > > > > +                                        pages, &new_acpi_addr);
> > > > > > > > > > > > +               if (ret != EFI_SUCCESS)
> > > > > > > > > > > > +                       return log_msg_ret("mem", -ENOMEM);
> > > > > > > > > > > > +
> > > > > > > > > > > > +               addr = (void *)(uintptr_t)new_acpi_addr;
> > > > > > > > > > > > +       }
> > > > > > > > > > > > +
> > > > > > > > > > >
> > > > > > > > > > > The tables should be written regardless of whether EFI_LOADER is enabled.
> > > > > > > > > >
> > > > > > > > > > *Why*? How do you expect to hand them over to the OS?
> > > > > > > > >
> > > > > > > > > Why - because boards which need ACPI tables to boot should generate
> > > > > > > > > them;
> > > > > > > >
> > > > > > > > Noone argued that.
> > > > > > > >
> > > > > > > > > also this happens when U-Boot starts up, in last_stage_init()
> > > > > > > > > How - it isn't possible, but eventually I suppose it will be, once we
> > > > > > > > > have a use case for booting with ACPI but without EFI
> > > > > > > >
> > > > > > > > Are you aware of such an OS? If not, we can accept the patches when we
> > > > > > > > have a reason.
> > > > > > >
> > > > > > > Which patches? This is how it works today. We set up the tables in
> > > > > > > last_stage_init(), so they can be examined while in U-Boot.
> > > > > >
> > > > > > What I mean, is that until we have a valid use case to store the ACPI
> > > > > > in a bloblist, I prefer them being allocated with proper EFI memory
> > > > > > backing
> > > > >
> > > > > I'm going to assert prior art here. If ARM is to have ACPI in U-Boot,
> > > > > it should follow the most recent x86 approach and store it in the
> > > > > bloblist. That is what the blloblist is for. It also avoids using
> > > > > memory below the U-Boot area, which is not allowed.
> > > > >
> > > > > >
> > > > > > >
> > > > > > > It is the patches to change this which I object to.
> > > > > > >
> > > > > > > > I remember patches being hard NAK'ed on using DTs to pass the ACPI
> > > > > > > > table address in the past.
> > > > > > >
> > > > > > > Yes, I believe Bytedance carries a patch locally for that :-)
> > > > > >
> > > > > > Exactly
> > > > > >
> > > > > > >
> > > > > > > >
> > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > > > Can we drop this else clause? We should always use the bloblist.
> > > > > > > > > >
> > > > > > > > > > Both Heinrich and I said the exact opposite. Unless there's a
> > > > > > > > > > perfectly good reason why we should keep them in bloblist memory, I'd
> > > > > > > > > > like us to do that
> > > > > > > > >
> > > > > > > > > The main reason is that we should not be putting things in memory
> > > > > > > > > between the start of RAM and the bottom of the U-Boot area. That
> > > > > > > > > region of memory is supposed to be for loading images. Most boards
> > > > > > > > > hard-code the image-load addresses in environment variables. But even
> > > > > > > > > if they didn't, we should not be using that memory for U-Boot data.
> > > > > > > >
> > > > > > > > EFI allows you to request a specific address to use. We can choose one
> > > > > > > > that fits the requirements
> > > > > > >
> > > > > > > So long as it is in U-Boot's space, that is fine. I just sent a patch
> > > > > > > about relocation which covers this. It occured to me that this feature
> > > > > > > of U-Boot, which I have always assumed was common knowledge, may have
> > > > > > > not been noticed.
> > > > > > >
> > > > > > > > >
> > > > > > > > > Another reason is that the bloblist is designed for this, for keeping
> > > > > > > > > tables in a small, contiguous area of memory, so that when passed to
> > > > > > > > > Linux they are not spread all over the place.
> > > > > > > >
> > > > > > > > Linux does not and will not read tables from a bloblist though
> > > > > > >
> > > > > > > Indeed. There really isn't any point, anyway, since there are other
> > > > > > > ways of passing the tables along...except for ACPI with FDT but that
> > > > > > > isn't a valid use case for Linux so far.
> > > > > >
> > > > > > What we are trying to do with EFI is to stay as close to the spec and
> > > > > > the current OS implementations as possible. So again, please allocate
> > > > > > EFI memory for the ACPI tables. The patches to convert it to bloblist
> > > > > > allocating them are minimal, so we can do it, once there's an actuall
> > > > > > need for it.
> > > > >
> > > > > As it stands today, efi_acpi_register() does not do an EFI allocation,
> > > > > it just adds the existing allocation to the EFI tables. This works
> > > > > fine for x86 - see arch/x86/lib/tables.c - so I would like ARM to do
> > > > > the same. The need for it is (as above) that we should ensure that
> > > > > memory usage is within the U-Boot area. This is something which
> > > > > bloblist handles automatically. It is also nice to see all the tables
> > > > > in one place with 'bloblist list'
> > > > >
> > > >
> > > > So what's the consent and the next step here?
> > > > Is the current code OK as is, as it works with both BLOBLIST and without?
> > > > Should I drop support for one or the other?
> > >
> > > Just BLOBLIST. The EFI allocation is done using efi_acpi.c which you
> > > can check to make sure it is working.
> > >
> > > Using efi_allocate_pages() before the app starts is not good.
> >
> > Simon, please stop trying to enforce decisions on subsystems you don't
> > maintain. I am pretty sure both Heinrich and I said no to this.
>
> I am the ACPI maintainer, and x86 maintainer long before ACPI came in
> for ARM (which I originally hacked together, as you know). I also
> wrote bloblist, including the header file which says:

That's not the EFI subsystem though. And last time I checked where the
ACPI tables are allocated makes no difference as long as they are
installed on a config table.

>
>  * 6. Bloblist is designed to be passed to Linux as reserved memory.
> While linux
>  * doesn't understand the bloblist header, it can be passed the indivdual blobs.

And as I already said, *when* bloblist is consumed by any OS and you
have a valid use case other than "I can do bloblist list and I like
it", you can change 3 lines of code and allocate the ACPI table there.

>  * For example, ACPI tables can reside in a blob and the address of those is
>  * passed to Linux, without Linux ever being away of the existence of a
>  * bloblist. Having all the blobs contiguous in memory simplifies the
>  * reserved-memory space.

No, it doesn't because all of the other tables are currently allocated
by the EFI subsystem. So it actually fragments it. Apart from that You
dont really know what the OS is going to do with that memory. It
depends on the EFI memory type and OS decisions.

>
> This decision has serious impacts on memory management in U-Boot. It
> also bears on the complexity of memory, how bootstd works, board
> scripts and the like. We should discuss this and figure out a path
> forward.

It has close to zero impact because *all* of the EFI memory lives in
top memory. So apart from the EFI_BOUNCE_BUFFER perhaps,  I don't see
why the impact is """serious""".
EFI allocates memory which does not affect U-Boot of file loading
apart from the max size allowed. Now with LMB it is marked as
reserved. So why is this any different from any other LMB reservation?
It's memory used by someone that you aren't allowed to use, just like
we reserve U-Boot memory. If there's a bug in reservations, by all
means, let's fix it.

Thanks
/Ilias

>
> Regards,
> Simon

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