From mboxrd@z Thu Jan  1 00:00:00 1970
From: linux@arm.linux.org.uk (Russell King - ARM Linux)
Date: Mon, 21 Sep 2009 09:41:55 +0100
Subject: Kernel related (?) user space crash at ARM11 MPCore
In-Reply-To: <20090921083109.GC20006@shareable.org>
References: <1250184014.14019.40.camel@pc1117.cambridge.arm.com>
	<1250501311.9858.24.camel@pc1117.cambridge.arm.com>
	<20090817140422.GA10764@n2100.arm.linux.org.uk>
	<1250529916.11185.80.camel@pc1117.cambridge.arm.com>
	<20090919224022.GA738@n2100.arm.linux.org.uk>
	<1253435940.498.15.camel@pc1117.cambridge.arm.com>
	<20090920093139.GA1704@n2100.arm.linux.org.uk>
	<20090920190227.GB5413@n2100.arm.linux.org.uk>
	<4AB6B0AB.8040307@arm.com> <20090921083109.GC20006@shareable.org>
Message-ID: <20090921084155.GB27357@n2100.arm.linux.org.uk>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Mon, Sep 21, 2009 at 09:31:09AM +0100, Jamie Lokier wrote:
> I'm not able to tell from this thread, and I don't have the hardware
> to test either:
> 
> I have some userspace ARM code which modifies instructions and data
> used by those instructions in a few pages, using mprotect() to make
> them writable, modify, and make them PROT_READ|PROT_EXEC again.
> 
> There is no execution of the modified code _during_ the modification,
> only afterwards.

We've had a syscall to handle the cache issues to do with self
modifying code - __ARM_NR_cacheflush.  See the comments associated
with 'cacheflush' in arch/arm/kernel/traps.c about how to use it.
This is the situation which the syscall was designed to address back
in the 1990s.