[U-Boot] [PATCH] [U-boot]: Change FDT memory typpe from runtime data to acpi reclaim

[Ard Biesheuvel]

(+ Leif)

On Thu, 11 Apr 2019 at 12:34, Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
>
> On 4/11/19 8:39 PM, Ilias Apalodimas wrote:
> > Following Ard's suggestion:
> > Runtime data sections are intended for data that is used by the runtime
> > services implementations.
> > Let's change they type to EFI_ACPI_RECLAIM_MEMORY
> >
> > Suggested-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> > Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
> > ---
> >   cmd/bootefi.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/cmd/bootefi.c b/cmd/bootefi.c
> > index 3619a20e6433..b54181909aff 100644
> > --- a/cmd/bootefi.c
> > +++ b/cmd/bootefi.c
> > @@ -111,13 +111,13 @@ static efi_status_t copy_fdt(void **fdtp)
> >       new_fdt_addr = (uintptr_t)map_sysmem(fdt_ram_start + 0x7f00000 +
> >                                            fdt_size, 0);
> >       ret = efi_allocate_pages(EFI_ALLOCATE_MAX_ADDRESS,
> > -                              EFI_RUNTIME_SERVICES_DATA, fdt_pages,
> > +                              EFI_ACPI_RECLAIM_MEMORY, fdt_pages,
>
> GRUB uses EfiLoaderCode when installing its modified version of the FDT.
>
> The "Embedded Base Boot Requirements (EBBR) Specification, Release v1.0"
> does not require ACPI support. Can we expect EfiACPIReclaimMemory to be
> supported if we do not have any ACPI table?
>

In spite of the name, ACPI reclaim memory is fully specified by the
UEFI spec, so whether you actually use ACPI or not is irrelevant. It
is memory that can be treated by the OS as conventional memory if it
doesn't care about preserving the contents.

> How about functions efi_smbios_register() and efi_acpi_register()?
>

SMBIOS uses RuntimeServicesData memory for historical reasons, but
that is basically a mistake.
ACPI tables should use ACPI reclaim memory, and even the allocations
they refer to (such as the bitmap referenced by the BGRT table) should
use ACPI reclaim memory, which is another thing we are trying to get
fixed in the spec.

> How about systab.tables assigned in efi_initialize_system_table()? Which
> of the addresses in systab.tables should be updated upon relocation.
>
> The EFI Spec is really hazy: "A pointer to the table associated with
> VendorGuid. Whether this pointer is a physical address or a
> virtual address during runtime is determined by the VendorGuid."
>

Indeed. So it is up to the publisher to update the reference, but I am
not aware of any firmware implementations that do this in practice. It
is typically assumed that a firmware component that is still active at
runtime holds its own reference to data exposed via a configuration
table, and updates the reference during SetVirtualAddressMap.

There is also a known bug in EDK2 where the ESRT table is passed in
boot services memory, but the capsule update code actually tries to
access it at runtime, so this isn't as clean as we'd like it to be.

> The FDT_TABLE_GUID or DEVICE_TREE_GUID as Linux calls it is not defined
> in the UEFI spec. So we can marvel about expected behavior. Is there any
> other document specifying it?
>

No, its de facto specification is in the EDK2 source tree.

Since there is no reason the firmware itself would need to consume the
device tree at runtime, there is no point in keeping it in
EfiRuntimeServicesData memory or in updating the configuration table
entry.