Fwd: Re: [PATCH] efi_loader: Omit memory with "no-map" when returning memory map.

[Heinrich Schuchardt]

-------- Ursprüngliche Nachricht --------
Von: Ard Biesheuvel <ardb at kernel.org>
Gesendet: 31. August 2021 12:33:56 MESZ
An: Heinrich Schuchardt <xypron.glpk at gmx.de>
CC: Kristian Amlie <kristian.amlie at northern.tech>
Betreff: Re: [PATCH] efi_loader: Omit memory with "no-map" when returning memory map.

On Tue, 31 Aug 2021 at 08:41, Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
>
> On 8/27/21 9:55 AM, Kristian Amlie wrote:
>
> You can use scripts/get_maintainer.pl to find the right addressees for
> your patches.
>
> > efi_reserve_memory() states that memory marked with "no-map" shall not
> > be accessed by the UEFI payload. Make sure efi_get_memory_map() honors
> > this.
> >

Accessing memory and describing memory are two different things.
Describing reserved memory in the memory map is important, because it
helps us distinguish it from MMIO regions.

> > This helps the case when booting vexpress_ca9x4 under QEMU. Because
> > the kernel wants to use an address in the lowest 128MiB of the range,
> > but this range is reserved with "no-map", the kernel complains that it
> > can not allocate the low memory it needs. In reality the actual usable
> > memory starts much higher, which is reflected correctly in the memory
> > map after this fix.
>

This is a u-boot patch right? (I cannot tell from the context, as
there are no mailing lists on cc)

It is u-boot's job to describe all the memory, no matter how it is
used. Even if the kernel itself may not use it as system memory, there
are cases where kernel infrastructure is used to map these regions:
for instance, the ACPI core may need to map a SystemMemory OpRegion,
and we need the EFI memory map to tell us whether to use memory or I/O
semantics.

As for the 128 MB issue: can you reproduce this with a recent kernel?
We made some changes recently to the EFI stub as well as the
decompressor code to prevent the decompressor code from relocating
itself to the base of DRAM, and to allow the decompressed kernel to
reside at any 2 MB aligned offset in memory.


> The 'no-map' requirement needs to be fulfilled by the kernel.
>
> The GetMemoryMap() boot time service must comply to the UEFI specification.
>
> The Devicetree Specification has this clarification:
>
> "Reserved regions with the no-map property must be listed in the memory
> map with type EfiReservedMemoryType. All other reserved regions must be
> listed with type EfiBootServicesData."
> https://devicetree-specification.readthedocs.io/en/latest/chapter3-devicenodes.html
>
> Should the kernel calculate its internal 128 MiB requirement incorrectly
> this needs be fixed in the kernel EFI stub. Does the problem exist with
> kernel 5.14?
>
> I wonder if the 128 MiB requirement of the kernel can be lifted for
> 32bit ARM as we already did for RISC-V. Cf.
>

As mentioned above, this should already be fixed, in v5.11 or later

> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.14&id=c79e89ecaa246c880292ba68cbe08c9c30db77e3
>
> Cc Ard, maintainer of the kernel EFI stub.
>
> Best regards
>
> Heinrich
>
> >
> > Signed-off-by: Kristian Amlie <kristian.amlie at northern.tech>
> > ---
> >   lib/efi_loader/efi_memory.c | 14 +++++++++++++-
> >   1 file changed, 13 insertions(+), 1 deletion(-)
> >
> > diff --git a/lib/efi_loader/efi_memory.c b/lib/efi_loader/efi_memory.c
> > index f4acbee4f9..7f8543143a 100644
> > --- a/lib/efi_loader/efi_memory.c
> > +++ b/lib/efi_loader/efi_memory.c
> > @@ -646,8 +646,16 @@ efi_status_t efi_get_memory_map(efi_uintn_t *memory_map_size,
> >
> >       provided_map_size = *memory_map_size;
> >
> > -     list_for_each(lhandle, &efi_mem)
> > +     list_for_each(lhandle, &efi_mem) {
> > +             struct efi_mem_list *lmem;
> > +
> > +             lmem = list_entry(lhandle, struct efi_mem_list, link);
> > +
> > +             if (lmem->desc.type == EFI_RESERVED_MEMORY_TYPE)
> > +                     continue;
> > +
> >               map_entries++;
> > +     }
> >
> >       map_size = map_entries * sizeof(struct efi_mem_desc);
> >
> > @@ -672,6 +680,10 @@ efi_status_t efi_get_memory_map(efi_uintn_t *memory_map_size,
> >               struct efi_mem_list *lmem;
> >
> >               lmem = list_entry(lhandle, struct efi_mem_list, link);
> > +
> > +             if (lmem->desc.type == EFI_RESERVED_MEMORY_TYPE)
> > +                     continue;
> > +
> >               *memory_map = lmem->desc;
> >               memory_map--;
> >       }
> >
>