On Thu, Jan 31, 2013 at 12:15:39PM +0000, Mark Rutland wrote:

Switching between reading the virtual or physical counters is
problematic, as some core code wants a view of time before we're fully
set up. Using a function pointer and switching the source after the
first read can make time appear to go backwards, and having a check in
the read function is an unfortunate block on what we want to be a fast
path.

Instead, this patch makes us always use the virtual counters. If we're a
guest, or don't have hyp mode, we'll use the virtual timers, and as such
don't care about CNTVOFF as long as it doesn't change in such a way as
to make time travel backwards. If we do have hyp mode, and might be a
KVM host, we have to use the physical timers, and require CNTVOFF to be
zero so as to have a consistent view of time between the physical timers
and virtual counters.

Any code which may want to alter CNTVOFF (e.g. KVM) will need to ensure
that it is zeroed when entering the host.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>

Acked-by: Catalin Marinas <catalin.marinas@arm.com>