[PATCH v5 03/20] arm64: Use physical counter for in-kernel reads when booted in EL2

[Catalin Marinas]

On Fri, Oct 27, 2017 at 10:34:24AM +0200, Christoffer Dall wrote:
> Using the physical counter allows KVM to retain the offset between the
> virtual and physical counter as long as it is actively running a VCPU.
> 
> As soon as a VCPU is released, another thread is scheduled or we start
> running userspace applications, we reset the offset to 0, so that
> userspace accessing the virtual timer can still read the virtual counter
> and get the same view of time as the kernel.
> 
> This opens up potential improvements for KVM performance, but we have to
> make a few adjustments to preserve system consistency.
> 
> Currently get_cycles() is hardwired to arch_counter_get_cntvct() on
> arm64, but as we move to using the physical timer for the in-kernel
> time-keeping on systems that boot in EL2, we should use the same counter
> for get_cycles() as for other in-kernel timekeeping operations.
> 
> Similarly, implementations of arch_timer_set_next_event_phys() is
> modified to use the counter specific to the timer being programmed.
> 
> VHE kernels or kernels continuing to use the virtual timer are
> unaffected.
> 
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Will Deacon <will.deacon at arm.com>
> Cc: Mark Rutland <mark.rutland at arm.com>
> Acked-by: Marc Zyngier <marc.zyngier at arm.com>
> Signed-off-by: Christoffer Dall <cdall at linaro.org>

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