linux-kernel - Re: [PATCH v2 1/2] arm64: dts: broadcom: bcmbca: bcm4908: Reserve CFE stub area

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Message-ID: <20241124175637.718510-1-florian.fainelli@broadcom.com>
Date: Sun, 24 Nov 2024 09:56:37 -0800
From: Florian Fainelli <florian.fainelli@...adcom.com>
To: bcm-kernel-feedback-list@...adcom.com,
	Sam Edwards <cfsworks@...il.com>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Rafał Miłecki <rafal@...ecki.pl>,
	William Zhang <william.zhang@...adcom.com>,
	Anand Gore <anand.gore@...adcom.com>,
	Kursad Oney <kursad.oney@...adcom.com>
Cc: Florian Fainelli <f.fainelli@...il.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Sam Edwards <CFSworks@...il.com>
Subject: Re: [PATCH v2 1/2] arm64: dts: broadcom: bcmbca: bcm4908: Reserve CFE stub area

From: Florian Fainelli <f.fainelli@...il.com>

On Fri,  4 Oct 2024 22:01:54 -0700, Sam Edwards <cfsworks@...il.com> wrote:
> The CFE bootloader places a stub program in the first page of physical
> memory to hold the secondary CPUs until the boot CPU writes the release
> address, but does not splice a /reserved-memory node into the FDT to
> protect it. If Linux overwrites this program before execution reaches
> smp_prepare_cpus(), the secondary CPUs may become inaccessible.
> 
> This is only a problem with CFE, and then only until the secondary CPUs
> are brought online. Ideally, there would be some hypothetical mechanism
> we could use to indicate that this area of memory is sensitive only
> during boot. But as there is none, and since it is such a small amount
> of memory, it is easiest to reserve it unconditionally.
> 
> Therefore, add a /reserved-memory node to bcm4908.dtsi to protect the
> first 4KiB of physical memory.
> 
> Signed-off-by: Sam Edwards <CFSworks@...il.com>
> ---

Applied to https://github.com/Broadcom/stblinux/commits/devicetree-arm64/next, thanks!
--
Florian