[PATCH] arm64: efi: don't restore TTBR0 if active_mm points at init_mm

[Catalin Marinas]

On Mon, Mar 23, 2015 at 05:22:57PM +0000, Jon Medhurst (Tixy) wrote:
> On Mon, 2015-03-23 at 15:44 +0000, Catalin Marinas wrote:
> > From 5d9e3540b6480558528612dd3672543fa8ab3528 Mon Sep 17 00:00:00 2001
> > From: Catalin Marinas <catalin.marinas at arm.com>
> > Date: Mon, 23 Mar 2015 15:06:50 +0000
> > Subject: [PATCH] arm64: Use the reserved TTBR0 if context switching to the
> >  init_mm
> > 
> > The idle_task_exit() function may call switch_mm() with next ==
> > &init_mm. On arm64, init_mm.pgd cannot be used for user mappings, so
> > this patch simply sets the reserved TTBR0.
> > 
> > Cc: <stable at vger.kernel.org>
> > Reported-by: Jon Medhurst (Tixy) <tixy at linaro.org>
> > Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
> 
> That unsurprising fixes the BUG_ON I was seeing on Juno, so...
> Tested-by: Jon Medhurst (Tixy) <tixy at linaro.org>

Thanks.

> One question, is bypassing setting the mm_cpumask and context.id for
> init_mm OK? I'm not familiar with the code but had a quick look, and it
> looks like they are just used for ASID management, in which case I
> assume everything is OK - ASIDs only being relevant for user mappings in
> ttbr0?

That's my thinking as well. Will asked me the same question, so I'll let
him confirm if he's seeing anything wrong.

-- 
Catalin