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

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Message-ID: <CAMj1kXEnxgsy6LkyWGFmwDxVroDofeGYdUd2BvfJ=bNgj0TYVg@mail.gmail.com>
Date: Tue, 10 Dec 2024 10:59:55 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Hamza Mahfooz <hamzamahfooz@...ux.microsoft.com>
Cc: 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 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>