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Subject: Re: [PATCH v12] ARM: uncompress: Validate start of physical memory
 against passed DTB
To:     Geert Uytterhoeven <geert+renesas@glider.be>,
        Russell King <linux@armlinux.org.uk>,
        Ard Biesheuvel <ardb@kernel.org>,
        Nicolas Pitre <nico@fluxnic.net>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Linus Walleij <linus.walleij@linaro.org>
Cc:     Arnd Bergmann <arnd@arndb.de>, Eric Miao <eric.miao@nvidia.com>,
        =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= <u.kleine-koenig@pengutronix.de>,
        Lukasz Stelmach <l.stelmach@samsung.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Chris Brandt <chris.brandt@renesas.com>,
        linux-arm-kernel@lists.infradead.org,
        linux-renesas-soc@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20210104130111.1269694-1-geert+renesas@glider.be>
From:   Dmitry Osipenko <digetx@gmail.com>
Message-ID: <5f23561e-4099-8578-2c28-4ba39bbaa071@gmail.com>
Date:   Sat, 9 Jan 2021 20:27:54 +0300
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04.01.2021 16:01, Geert Uytterhoeven пишет:
> Currently, the start address of physical memory is obtained by masking
> the program counter with a fixed mask of 0xf8000000.  This mask value
> was chosen as a balance between the requirements of different platforms.
> However, this does require that the start address of physical memory is
> a multiple of 128 MiB, precluding booting Linux on platforms where this
> requirement is not fulfilled.
> 
> Fix this limitation by validating the masked address against the memory
> information in the passed DTB.  Only use the start address
> from DTB when masking would yield an out-of-range address, prefer the
> traditional method in all other cases.  Note that this applies only to the
> explicitly passed DTB on modern systems, and not to a DTB appended to
> the kernel, or to ATAGS.  The appended DTB may need to be augmented by
> information from ATAGS, which may need to rely on knowledge of the start
> address of physical memory itself.
> 
> This allows to boot Linux on r7s9210/rza2mevb using the 64 MiB of SDRAM
> on the RZA2MEVB sub board, which is located at 0x0C000000 (CS3 space),
> i.e. not at a multiple of 128 MiB.
> 
> Suggested-by: Nicolas Pitre <nico@fluxnic.net>
> Suggested-by: Ard Biesheuvel <ardb@kernel.org>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
> Acked-by: Nicolas Pitre <nico@fluxnic.net>
> ---
> Submitted to RMK's patch tracker.
> 
> v12:
>   - Drop unneeded initialization of r in get_val(),

I tested this patch on NVIDIA Tegra and haven't spotted any problems.

Tested-by: Dmitry Osipenko <digetx@gmail.com>