KVM: arm64: timers: Correctly handle TGE flip with CNTPOFF_EL2

Contrary to common belief, HCR_EL2.TGE has a direct and immediate
effect on the way the EL0 physical counter is offset. Flipping
TGE from 1 to 0 while at EL2 immediately changes the way the counter
compared to the CVAL limit.

This means that we cannot directly save/restore the guest's view of
CVAL, but that we instead must treat it as if CNTPOFF didn't exist.
Only in the world switch, once we figure out that we do have CNTPOFF,
can we must the offset back and forth depending on the polarity of
TGE.

Fixes: 2b4825a86940 ("KVM: arm64: timers: Use CNTPOFF_EL2 to offset the physical timer")
Reported-by: Ganapatrao Kulkarni <gankulkarni@os.amperecomputing.com>
Tested-by: Ganapatrao Kulkarni <gankulkarni@os.amperecomputing.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h
index bb3cb005873e..e748bc957d83 100644
--- a/include/kvm/arm_arch_timer.h
+++ b/include/kvm/arm_arch_timer.h
@@ -82,6 +82,8 @@ struct timer_map {
 	struct arch_timer_context *emul_ptimer;
 };
 
+void get_timer_map(struct kvm_vcpu *vcpu, struct timer_map *map);
+
 struct arch_timer_cpu {
 	struct arch_timer_context timers[NR_KVM_TIMERS];
 
@@ -145,4 +147,9 @@ u64 timer_get_cval(struct arch_timer_context *ctxt);
 void kvm_timer_cpu_up(void);
 void kvm_timer_cpu_down(void);
 
+static inline bool has_cntpoff(void)
+{
+	return (has_vhe() && cpus_have_final_cap(ARM64_HAS_ECV_CNTPOFF));
+}
+
 #endif