@@ -148,11 +148,13 @@ static inline void arch_timer_set_cntkctl(u32 cntkctl)
static inline u64 arch_counter_get_cntpct(void)
{
+ u64 cval;
/*
* AArch64 kernel and user space mandate the use of CNTVCT.
*/
- BUG();
- return 0;
+ isb();
+ asm volatile("mrs %0, cntpct_el0" : "=r" (cval));
+ return cval;
}
static inline u64 arch_counter_get_cntvct(void)
@@ -886,8 +886,7 @@ static void __init arch_counter_register(unsigned type)
/* Register the CP15 based counter if we have one */
if (type & ARCH_TIMER_TYPE_CP15) {
- if (IS_ENABLED(CONFIG_ARM64) ||
- arch_timer_uses_ppi == ARCH_TIMER_VIRT_PPI)
+ if (arch_timer_uses_ppi == ARCH_TIMER_VIRT_PPI)
arch_timer_read_counter = arch_counter_get_cntvct;
else
arch_timer_read_counter = arch_counter_get_cntpct;
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 cirtual counter and get the same view of time as the kernel. This opens up potential improvements for KVM performance. VHE kernels or kernels continuing to use the virtual timer should be unaffected. Signed-off-by: Christoffer Dall <cdall@linaro.org> --- arch/arm64/include/asm/arch_timer.h | 6 ++++-- drivers/clocksource/arm_arch_timer.c | 3 +-- 2 files changed, 5 insertions(+), 4 deletions(-)