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

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Message-ID: <78f25b22-f35b-4183-baec-7ddc0c5e3fda@broadcom.com>
Date: Thu, 3 Oct 2024 15:41:17 -0700
From: Florian Fainelli <florian.fainelli@...adcom.com>
To: Sam Edwards <cfsworks@...il.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: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>,
 Broadcom internal kernel review list
 <bcm-kernel-feedback-list@...adcom.com>, devicetree@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: broadcom: bcmbca: bcm4908: Reserve CFE stub
 area

On 10/3/24 14:30, Sam Edwards wrote:
> The CFE bootloader places a stub program at 0x0000-0xFFFF to hold the
> secondary CPUs until the boot CPU writes the release address. 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. However, 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 this
> critical memory region.
> 
> Signed-off-by: Sam Edwards <CFSworks@...il.com>

Not objecting to the solution, but should not this be moved to a 
per-board DTS given that there are boards using CFE, and some using 
u-boot + ARM TF that are unlikely to suffer from that problem?

-- 
Florian