linux-kernel - Re: [PATCH] arm: Handle starting up in secure mode

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Message-ID: <55DF3807.40506@linaro.org>
Date:	Thu, 27 Aug 2015 17:17:11 +0100
From:	Daniel Thompson <daniel.thompson@...aro.org>
To:	Christopher Covington <cov@...eaurora.org>
Cc:	Russell King <linux@....linux.org.uk>,
	Will Deacon <will.deacon@....com>,
	Mark Rutland <mark.rutland@....com>,
	Nicolas Pitre <nico@...aro.org>,
	"Jon Medhurst (Tixy)" <tixy@...aro.org>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Wang Nan <wangnan0@...wei.com>,
	Nathan Lynch <nathan_lynch@...tor.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Yingjoe Chen <yingjoe.chen@...iatek.com>,
	Masahiro Yamada <yamada.m@...panasonic.com>,
	Gregory CLEMENT <gregory.clement@...e-electrons.com>,
	Arnd Bergmann <arnd@...db.de>,
	Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
	Kees Cook <keescook@...omium.org>,
	Florian Fainelli <f.fainelli@...il.com>,
	Maxime Coquelin stm32 <mcoquelin.stm32@...il.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Paul Bolle <pebolle@...cali.nl>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm: Handle starting up in secure mode

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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