Re: [PATCH] efi: bump up EFI_MMAP_NR_SLACK_SLOTS to 32

[Ard Biesheuvel <ardb@kernel.org>]

On Tue, 31 Dec 2024 at 12:12, Víctor Gonzalo
<victor.gonzalo@anddroptable.net> wrote:
>
> El jue, 19 dic 2024 a las 12:27, Ard Biesheuvel (<ardb@kernel.org>) escribió:
> >
> > On Tue, 10 Dec 2024 at 10:59, Ard Biesheuvel <ardb@kernel.org> wrote:
> > >
> > > On Mon, 9 Dec 2024 at 19:20, Hamza Mahfooz
> > > <hamzamahfooz@linux.microsoft.com> wrote:
> > > >
> > > > Recent platforms require more slack slots than the current value of
> > > > EFI_MMAP_NR_SLACK_SLOTS, otherwise they fail to boot. The current
> > > > workaround is to append `efi=disable_early_pci_dma` to the kernel's
> > > > cmdline. So, bump up EFI_MMAP_NR_SLACK_SLOTS to 32 to allow those
> > > > platforms to boot with the aforementioned workaround.
> > > >
> > > > Cc: stable@kernel.org
> > > > Cc: Ard Biesheuvel <ardb@kernel.org>
> > > > Cc: Allen Pais <apais@linux.microsoft.com>
> > > > Cc: Tyler Hicks <code@tyhicks.com>
> > > > Signed-off-by: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
> > > > ---
> > > >  drivers/firmware/efi/libstub/efistub.h | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
> > > > index 76e44c185f29..e95ce6ae5c26 100644
> > > > --- a/drivers/firmware/efi/libstub/efistub.h
> > > > +++ b/drivers/firmware/efi/libstub/efistub.h
> > > > @@ -171,7 +171,7 @@ void efi_set_u64_split(u64 data, u32 *lo, u32 *hi)
> > > >   * the EFI memory map. Other related structures, e.g. x86 e820ext, need
> > > >   * to factor in this headroom requirement as well.
> > > >   */
> > > > -#define EFI_MMAP_NR_SLACK_SLOTS        8
> > > > +#define EFI_MMAP_NR_SLACK_SLOTS        32
> > > >
> > > >  typedef struct efi_generic_dev_path efi_device_path_protocol_t;
> > > >
> > >
> > > Acked-by: Ard Biesheuvel <ardb@kernel.org>
> >
> > I've queued this up for v6.14 now - once we are confident it does not
> > cause any regressions, we can backport it to stable branches too.
> >
>
> Hi. I had this issue three years ago, suggested the bump and then
> missed the reply.
> We bumped it to 16 and have not had any issue or side effects in three years.

Thanks for the data point.