linux-kernel - Re: [PATCH -next,v2] efi/libstub: arm32: Use "align" for the size alignment

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Date:   Thu, 4 Nov 2021 10:26:38 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Gaosheng Cui <cuigaosheng1@...wei.com>
Cc:     linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        wangweiyang2@...wei.com
Subject: Re: [PATCH -next,v2] efi/libstub: arm32: Use "align" for the size alignment

On Tue, 2 Nov 2021 at 03:04, Gaosheng Cui <cuigaosheng1@...wei.com> wrote:
>
> We are doing page-based allocations, and both the address
> and size must meet alignment constraints, so using "align"
> for the size alignment is a better choice.
>

Why is it a better choice? If I allocate a 2 MB aligned block of
memory, why is it better to align the size to a multiple of 2 MB as
well?


> Signed-off-by: Gaosheng Cui <cuigaosheng1@...wei.com>
> ---
>  drivers/firmware/efi/libstub/randomalloc.c | 2 +-
>  drivers/firmware/efi/libstub/relocate.c    | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/firmware/efi/libstub/randomalloc.c b/drivers/firmware/efi/libstub/randomalloc.c
> index 724155b9e10d..7b7159bb035d 100644
> --- a/drivers/firmware/efi/libstub/randomalloc.c
> +++ b/drivers/firmware/efi/libstub/randomalloc.c
> @@ -76,7 +76,7 @@ efi_status_t efi_random_alloc(unsigned long size,
>         if (align < EFI_ALLOC_ALIGN)
>                 align = EFI_ALLOC_ALIGN;
>
> -       size = round_up(size, EFI_ALLOC_ALIGN);
> +       size = round_up(size, align);
>
>         /* count the suitable slots in each memory map entry */
>         for (map_offset = 0; map_offset < map_size; map_offset += desc_size) {
> diff --git a/drivers/firmware/efi/libstub/relocate.c b/drivers/firmware/efi/libstub/relocate.c
> index 8ee9eb2b9039..d6d27e8c23f8 100644
> --- a/drivers/firmware/efi/libstub/relocate.c
> +++ b/drivers/firmware/efi/libstub/relocate.c
> @@ -50,7 +50,7 @@ efi_status_t efi_low_alloc_above(unsigned long size, unsigned long align,
>         if (align < EFI_ALLOC_ALIGN)
>                 align = EFI_ALLOC_ALIGN;
>
> -       size = round_up(size, EFI_ALLOC_ALIGN);
> +       size = round_up(size, align);
>         nr_pages = size / EFI_PAGE_SIZE;
>         for (i = 0; i < map_size / desc_size; i++) {
>                 efi_memory_desc_t *desc;
> --
> 2.30.0
>