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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Thu, 9 Sep 2021 13:29:11 +0200
Message-ID: <CAMj1kXGej8Ps425A-UXmW19B45_EP89-YzpwdOYQ1C-DOVLvUg@mail.gmail.com>
Subject: Re: [PATCH v2] ARM: decompress: Use /memreserve/ DTS nodes when
 validating memory
To:     Bert Vermeulen <bert@biot.com>
Cc:     Russell King <linux@armlinux.org.uk>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Nicolas Pitre <nico@fluxnic.net>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        John Crispin <john@phrozen.org>
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On Tue, 7 Sept 2021 at 16:57, Bert Vermeulen <bert@biot.com> wrote:
>
> If the bootloader needs the start of memory to be preserved, for example
> because it dropped the Trusted Firmware blob there, this chunk of memory
> shouldn't be used by the kernel.
>
> To avoid adding yet another SoC-specific text offset to arch/arm/Makefile,
> this patch allows for a /memreserve/ entry in the DTS to mark off the
> memory chunk instead.
>
> Signed-off-by: Bert Vermeulen <bert@biot.com>

Thanks for working on this - I hope this will allow us to phase out at
least some of the existing text_offset hacks too.

Acked-by: Ard Biesheuvel <ardb@kernel.org>

> ---
>  arch/arm/boot/compressed/fdt_check_mem_start.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/boot/compressed/fdt_check_mem_start.c b/arch/arm/boot/compressed/fdt_check_mem_start.c
> index 62450d824c3c..1d47de1e860b 100644
> --- a/arch/arm/boot/compressed/fdt_check_mem_start.c
> +++ b/arch/arm/boot/compressed/fdt_check_mem_start.c
> @@ -64,7 +64,7 @@ uint32_t fdt_check_mem_start(uint32_t mem_start, const void *fdt)
>         uint32_t addr_cells, size_cells, base;
>         uint32_t fdt_mem_start = 0xffffffff;
>         const fdt32_t *reg, *endp;
> -       uint64_t size, end;
> +       uint64_t rsvaddr, size, end;
>         const char *type;
>         int offset, len;
>
> @@ -74,6 +74,19 @@ uint32_t fdt_check_mem_start(uint32_t mem_start, const void *fdt)
>         if (fdt_magic(fdt) != FDT_MAGIC)
>                 return mem_start;
>
> +       for (offset = fdt_off_mem_rsvmap(fdt); ; offset += 16) {
> +               rsvaddr = get_val(fdt + offset, 2);
> +               size = get_val(fdt + offset + 8, 2);
> +
> +               if (!rsvaddr && !size)
> +                       break;
> +
> +               end = rsvaddr + size;
> +               if (mem_start >= rsvaddr && mem_start <= end)
> +                       /* Relocate past reserved block */
> +                       mem_start = round_up(end, SZ_2M);
> +       }
> +
>         /* There may be multiple cells on LPAE platforms */
>         addr_cells = get_cells(fdt, "#address-cells");
>         size_cells = get_cells(fdt, "#size-cells");
> --
> 2.25.1
>