linux-kernel - Re: [PATCH v3 1/3] dt-bindings: reserved-memory: rmtfs: Allow guard pages

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Date:   Sat, 23 Sep 2023 19:46:00 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Bjorn Andersson <quic_bjorande@...cinc.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>
Cc:     linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] dt-bindings: reserved-memory: rmtfs: Allow guard
 pages

On 21/09/2023 04:37, Bjorn Andersson wrote:
> On some Qualcomm platforms the firwmare, or hardware, does not
> gracefully handle memory protection of the rmtfs memory region when
> placed adjacent to other protected region. Some DeviceTree authors have
> worked around this issue by explicitly reserving the space around the
> region, but this prevents such author to use rely on the OS to place the
> region, through the use of "size" (instead of a fixed location).
> 


Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>

> +
> +      When this is set, the first and last 4kB should be left unused, and the
> +      effective size of the region will thereby shrink with 8kB.

Maybe we should not reference the actual size (4 and 8 kB), but rather
page - "the first and last pages in mapping should be left unused ..." etc?



Best regards,
Krzysztof