linux-kernel - Re: [PATCH] efi: bump up EFI_MMAP_NR_SLACK

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Message-ID: <CAGRPHEJuJfJ+k72bDKVt=MgbKi3O1e-Zf+9kFTm2aN2naEzbDw@mail.gmail.com>
Date: Tue, 31 Dec 2024 13:11:55 +0200
From: Víctor Gonzalo <victor.gonzalo@...droptable.net>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Hamza Mahfooz <hamzamahfooz@...ux.microsoft.com>, linux-efi@...r.kernel.org, 
	stable@...nel.org, Allen Pais <apais@...ux.microsoft.com>, 
	Tyler Hicks <code@...icks.com>, 
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>, 
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Jonathan Marek <jonathan@...ek.ca>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] efi: bump up EFI_MMAP_NR_SLACK_SLOTS to 32

El jue, 19 dic 2024 a las 12:27, Ard Biesheuvel (<ardb@...nel.org>) escribió:
>
> On Tue, 10 Dec 2024 at 10:59, Ard Biesheuvel <ardb@...nel.org> wrote:
> >
> > On Mon, 9 Dec 2024 at 19:20, Hamza Mahfooz
> > <hamzamahfooz@...ux.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@...nel.org
> > > Cc: Ard Biesheuvel <ardb@...nel.org>
> > > Cc: Allen Pais <apais@...ux.microsoft.com>
> > > Cc: Tyler Hicks <code@...icks.com>
> > > Signed-off-by: Hamza Mahfooz <hamzamahfooz@...ux.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@...nel.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.