[PATCH v10 4/6] ARM: add vdso user-space code

[Catalin Marinas]

On Wed, Feb 25, 2015 at 11:56:36AM -0500, Christopher Covington wrote:
> On 02/24/2015 05:17 AM, Catalin Marinas wrote:
> > Writing CNTFRQ from non-secure mode would trap as well.
> 
> Are you saying it could A) cause an exception targeting the current EL/mode
> but not others, or B) cause an exception targeting the current or another EL/mode?

IIRC, it only traps at the current mode (if non-secure EL1 or EL2).

> > The detection mechanism would have to involve trapping of an undefined
> > instruction but it doesn't need to be done early during boot.
> 
> I put detection during early boot because I wanted to potentially change
> ELs/modes during early boot.

Yes, but it is simpler to install an undef hook later in the boot
process.

-- 
Catalin