Re: [Xen-devel] [PATCH] xen/arm: Blacklist the memory mapped timer (armv7-timer-mem)

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2015-01-14 at 16:03 +0000, Julien Grall wrote:
> Hi Ian,
> 
> On 14/01/15 11:02, Ian Campbell wrote:
> > On Tue, 2015-01-13 at 20:07 +0000, Julien Grall wrote:
> >> Some platform (such as the VFP Base AEMv8 model) has a memory mapped
> >> timer. We don't want DOM0 use this timer rather than the generic ARM
> >> timer. So blacklist it for all platforms.
> > 
> > It seems that these registers contain things like the ability to stop
> > the counter or change its frequency. So we certainly don't want dom0
> > getting at those!
> > 
> > It's not clear to me if accesses to these registers are trapped
> > according to the controls available for the CP registers, or if we would
> > have to resort to trapping the entire MMIO page if we wanted to support
> > access to these registers (I don't think we would want to anyway).
> 
> I didn't find any spec for the memory mapped timer. But looking to the
> driver, it looks like they also have the concept of physical/virtual. So
> we may not need to trap.
> 
> Anyway, before implementing anything I'd like to find the corresponding
> spec.

It's in the ARM ARM, Appendix E of v7, plus references from Chapter B8.

I'd imagine it was in the v8 ARM ARM too, but I've not looked.

Ian.


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