Re: [PATCH v2 1/3] ARM: catch pending imprecise abort on unmask

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Thu, Oct 15, 2015 at 08:39:15AM -0700, Tony Lindgren wrote:
> * Russell King - ARM Linux <linux@arm.linux.org.uk> [151015 08:37]:
> > On Thu, Oct 15, 2015 at 12:32:20PM +0200, Lucas Stach wrote:
> > > Install a non-faulting handler just before unmasking imprecise aborts
> > > and switch back to the regular one after unmasking is done.
> > > 
> > > This catches any pending imprecise abort that the firmware/bootloader
> > > may have left behind that would normally crash the kernel at that point.
> > > As there are apparently a lot of bootlaoders out there that do such a
> > > thing it makes sense to handle it in the common startup code.
> > > 
> > > Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
> > 
> > Much better.  Please feel free to add it to the patch system, thanks.
> > 
> > I think, given that the original seems to be breaking platforms, this
> > patch needs to go into -rc kernels, right?
> 
> Hmm do we still see a trace where the issue happened though with this
> one?

That's not the intention of this specific patch.

This is solely to detect the bootloader induced imprecise exception,
nothing more.  A backtrace for that won't be useful in any shape or
form - in fact, the backtrace will be well known (it'll be from the
site where the imprecise exceptions are unmasked.)

Any imprecise exception which happens after this will be handled in
the normal way: it'll raise a kernel oops, and that will have all the
details that a kernel oops normally has.

The difference is, rather than the boot loader provoking the kernel to
oops at this point, we're able to report the event and continue on.

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