linux-kernel - Re: [PATCH] ARM: decompress: Use /memreserve/ DTS nodes when validating memory

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Date:   Tue, 7 Sep 2021 10:16:28 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Bert Vermeulen <bert@...t.com>
Cc:     Russell King <linux@...linux.org.uk>,
        Ard Biesheuvel <ardb@...nel.org>,
        Nicolas Pitre <nico@...xnic.net>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        John Crispin <john@...ozen.org>
Subject: Re: [PATCH] ARM: decompress: Use /memreserve/ DTS nodes when
 validating memory

Hoi Bert,

On Mon, Sep 6, 2021 at 12:00 PM Bert Vermeulen <bert@...t.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@...t.com>

Thanks for your patch!

> --- 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, 8);
> +               size = get_val(fdt + offset + 8, 8);

The last parameter of get_val() is the number of cells, not the number
of bytes. Hence it should be 2 for the 64-bit values in the memory
reservation block.

The rest looks good to me.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds