linux-kernel - Re: [PATCH] arm64: tegra: only map accessible sysram

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Message-ID: <5d2e47ec-8304-d648-9c4a-80c7c02050a9@wwwdotorg.org>
Date:   Sun, 29 Sep 2019 23:28:43 -0600
From:   Stephen Warren <swarren@...dotorg.org>
To:     Mian Yousaf Kaukab <ykaukab@...e.de>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        treding@...dia.com, jonathanh@...dia.com,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH] arm64: tegra: only map accessible sysram

On 9/29/19 2:08 PM, Mian Yousaf Kaukab wrote:
> Most of the SysRAM is secure and only accessible by TF-A.
> Don't map this inaccessible memory in kernel. Only map pages
> used by bpmp driver.

I don't believe this change is correct. The actual patch doesn't
implement mapping a subset of the RAM (a software issue), but rather it
changes the DT representation of the SYSRAM hardware. The SYSRAM
hardware always does start at 0x30000000, even if a subset of the
address range is dedicated to a specific purpose. If the kernel must map
only part of the RAM, then some additional property should indicate
this. Also, I believe it's incorrect to hard-code into the kernel's DT
the range of addresses used by the secure monitor/OS, since this can
vary depending on what the user actually chooses to install as the
secure monitor/OS. Any indication of such regions should be filled in at
runtime by some boot firmware or the secure monitor/OS itself, or
retrieved using some runtime API rather than DT.