clocksource: arch_timer: use virtual counters

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 appear to travel backwards. As the guest will use the
virtual timers, a (potential) KVM host must use the physical timers
(which can wake up the host even if they fire while a guest is
executing), and hence a host must have CNTVOFF set to zero so as to have
a consistent view of time between the physical timers and virtual
counters.

Signed-off-by: Mark Rutland <[email protected]>
Acked-by: Catalin Marinas <[email protected]>
Acked-by: Marc Zyngier <[email protected]>
Acked-by: Santosh Shilimkar <[email protected]>
Cc: Rob Herring <[email protected]>

0 files changed, 0 insertions, 0 deletions