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

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Message-ID: <CAMj1kXHrNXdXHCF9vVOA3jsLTkcxRB3dX6SL8BbPbECugPsbLQ@mail.gmail.com>
Date: Tue, 7 Jan 2025 08:36:40 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Víctor Gonzalo <victor.gonzalo@...droptable.net>
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

On Tue, 31 Dec 2024 at 12:12, Víctor Gonzalo
<victor.gonzalo@...droptable.net> wrote:
>
> 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.

Thanks for the data point.