Increasing EFI_MMAP_NR_SLACK_SLOTS

Increasing EFI_MMAP_NR_SLACK_SLOTS

[Víctor Gonzalo]

Hello

I had an issue in a big server in which no linux distro I tried was
able to boot. It failed with the messages:

EFI stub: ERROR: exit_boot() failed!
EFI stub: ERROR: efi_main() failed!

Digging through the rabbit hole I reached the error in the call to
efi_bs_call(get_memory_map) inside efi_exit_boot_services() in
efi-stub-helper.c which returned EFI_BUFFER_TOO_SMALL, so everything
collapsed after that.

It looks like despite what the comment suggests, the headroom was not enough.
I fixed it by increasing the value of EFI_MMAP_NR_SLACK_SLOTS to 16.

Is this the right approach to fix the issue?
Would it be ok to change the value in the mainline?

Thanks
- Víctor

Re: Increasing EFI_MMAP_NR_SLACK_SLOTS

[Ard Biesheuvel]

On Fri, 3 Sept 2021 at 00:26, Víctor Gonzalo
<victor.gonzalo@anddroptable.net> wrote:
>
> Hello
>
> I had an issue in a big server in which no linux distro I tried was
> able to boot. It failed with the messages:
>
> EFI stub: ERROR: exit_boot() failed!
> EFI stub: ERROR: efi_main() failed!
>
> Digging through the rabbit hole I reached the error in the call to
> efi_bs_call(get_memory_map) inside efi_exit_boot_services() in
> efi-stub-helper.c which returned EFI_BUFFER_TOO_SMALL, so everything
> collapsed after that.
>
> It looks like despite what the comment suggests, the headroom was not enough.
> I fixed it by increasing the value of EFI_MMAP_NR_SLACK_SLOTS to 16.
>
> Is this the right approach to fix the issue?
> Would it be ok to change the value in the mainline?
>

I don't think changing that would be a problem. Patches welcome.