Subject: Re: [PATCH] arm: Handle starting up in secure mode
To: Christopher Covington <cov@codeaurora.org>
References: <1440424572-27116-1-git-send-email-cov@codeaurora.org>
Cc: Russell King <linux@arm.linux.org.uk>, Will Deacon <will.deacon@arm.com>,
        Mark Rutland <mark.rutland@arm.com>, Nicolas Pitre <nico@linaro.org>,
        "Jon Medhurst (Tixy)" <tixy@linaro.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Wang Nan <wangnan0@huawei.com>, Nathan Lynch <nathan_lynch@mentor.com>,
        Stephen Boyd <sboyd@codeaurora.org>,
        Yingjoe Chen <yingjoe.chen@mediatek.com>,
        Masahiro Yamada <yamada.m@jp.panasonic.com>,
        Gregory CLEMENT <gregory.clement@free-electrons.com>,
        Arnd Bergmann <arnd@arndb.de>,
        =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= <u.kleine-koenig@pengutronix.de>,
        Kees Cook <keescook@chromium.org>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Maxime Coquelin stm32 <mcoquelin.stm32@gmail.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Paul Bolle <pebolle@tiscali.nl>, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org
From: Daniel Thompson <daniel.thompson@linaro.org>
Message-ID: <55DF3807.40506@linaro.org>
Date: Thu, 27 Aug 2015 17:17:11 +0100
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On 24/08/15 14:55, Christopher Covington wrote:
> ARM Linux appears to have never been made aware of the ARMv7 security
> extensions. When CONFIG_ARM_SEC_EXT=y, have it probe for its security
> state by checking whether CNTFRQ is writeable and potentially make
> mode changes based on the information. The most features are available
> from hypervisor (HYP) mode, so switch to it possible. Failing that,
> prefer non-secure supervisor (SVC) mode to secure supervisor mode.

If there is no hypervisor mode available what benefit do we get from 
transitioning to non-secure mode?

When running in secure mode we retain access to some potentially useful 
features such as having access to FIQ.


Daniel.

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