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

From	Florian Fainelli <f.fainelli@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH V2] ARM: dts: bcm283x: Reserve first page for firmware
Date	2017-05-09 18:30 +0200
Message-ID	<tFgbo-4bu-13@gated-at.bofh.it> (permalink)
References	<tF9jz-89r-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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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@raspberrypi.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

Thread

[PATCH V2] ARM: dts: bcm283x: Reserve first page for firmware Phil Elwell <phil@raspberrypi.org> - 2017-05-09 11:10 +0200
  Re: [PATCH V2] ARM: dts: bcm283x: Reserve first page for firmware Florian Fainelli <f.fainelli@gmail.com> - 2017-05-09 18:30 +0200
  Re: [PATCH V2] ARM: dts: bcm283x: Reserve first page for firmware Florian Fainelli <f.fainelli@gmail.com> - 2017-05-09 19:00 +0200
    Re: [PATCH V2] ARM: dts: bcm283x: Reserve first page for firmware Eric Anholt <eric@anholt.net> - 2017-05-09 20:20 +0200
  Re: [PATCH V2] ARM: dts: bcm283x: Reserve first page for firmware Eric Anholt <eric@anholt.net> - 2017-05-09 19:00 +0200

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