linux-kernel - Re: [PATCH V2] ARM: dts: bcm283x: Reserve first page for firmware

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Date:   Tue, 9 May 2017 09:25:54 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Phil Elwell <phil@...pberrypi.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        Florian Fainelli <f.fainelli@...il.com>,
        bcm-kernel-feedback-list@...adcom.com, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org
Subject: Re: [PATCH V2] ARM: dts: bcm283x: Reserve first page for firmware

On 05/09/2017 02:04 AM, Phil Elwell wrote:
> The Raspberry Pi startup stub files for multi-core BCM27XX processors
> make the secondary CPUs spin until the corresponding mailbox is
> written. These stubs are loaded at physical address 0x00000xxx (as seen
> by the ARMs), but this page will be reused by the kernel unless it is
> explicitly reserved, causing the waiting cores to execute random code.
> 
> Use the /memreserve/ Device Tree directive to mark the first page as
> off-limits to the kernel.

This reserves a 4KB page here, is this good enough, or should we just go
directly to the maximum page granule size possible on an ARM64/Linux
system to be on the safe side?

> 
> See: https://github.com/raspberrypi/linux/issues/1989
> 
> Signed-off-by: Phil Elwell <phil@...pberrypi.org>
> ---
> 
> Changes in V2:
> - Rebase against linux-next
> - Drop downstream-only patch
> 
>  arch/arm/boot/dts/bcm283x.dtsi | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/arm/boot/dts/bcm283x.dtsi b/arch/arm/boot/dts/bcm283x.dtsi
> index a3106aa..6d12c3e8 100644
> --- a/arch/arm/boot/dts/bcm283x.dtsi
> +++ b/arch/arm/boot/dts/bcm283x.dtsi
> @@ -3,6 +3,8 @@
>  #include <dt-bindings/clock/bcm2835-aux.h>
>  #include <dt-bindings/gpio/gpio.h>
>  
> +/memreserve/ 0x00000000 0x00001000;

Can you put a comment above this /memreserve entry here to remind about
what this is useful for?

Thanks!

> +
>  /* This include file covers the common peripherals and configuration between
>   * bcm2835 and bcm2836 implementations, leaving the CPU configuration to
>   * bcm2835.dtsi and bcm2836.dtsi.
> 


-- 
Florian