ARM errata 430973 on multi platform kernels

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Fri, Apr 24, 2015 at 10:54:29AM +0200, Matthijs van Duin wrote:
> On 23 April 2015 at 12:25, Russell King - ARM Linux
> <linux@arm.linux.org.uk> wrote:
> > And you can't detect whether you're running in secure mode or not.
> 
> If not, you get an undefined instruction exception, which you could trap.
> 
> This may not be convenient, but "can't detect" is an overstatement.

It's these kinds of statements that really piss me off.

At this stage in the boot, there's no memory allocators.  There's no
MMU.  There's really not very much.  There's no guarantee that the
location where the vectors are is writable on all platforms.

It's pretty much _impossible_ to do generically.

"Can't detect" is _not_ an overstatement.  It's a statement that I'm
giving you through my experience and knowledge of the Linux kernel,
the ARM archtecture, the capabilities of the platforms we have to
deal with, and how we want the kernel to work.

Sure, we _can_ detect it if (and only if) we code specifically for a
platform which has RAM at the CPU vector location.  Unfortunately,
that's a _very_ small proportion which approximates a number very
close to zero.

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