KVM: arm64: timers: Use CNTPOFF_EL2 to offset the physical timer

With ECV and CNTPOFF_EL2, it is very easy to offer an offset for
the physical timer. So let's do just that.

Nothing can set the offset yet, so this should have no effect
whatsoever (famous last words...).

Reviewed-by: Colton Lewis <[e-mail]>
Signed-off-by: Marc Zyngier <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/arm64/kvm/arch_timer.c

···
 			      struct arch_timer_context *timer,
 			      enum kvm_arch_timer_regs treg);
 
+static bool has_cntpoff(void)
+{
+	return (has_vhe() && cpus_have_final_cap(ARM64_HAS_ECV_CNTPOFF));
+}
+
 u32 timer_get_ctl(struct arch_timer_context *ctxt)
 {
 	struct kvm_vcpu *vcpu = ctxt->vcpu;
···
 
 static u64 timer_get_offset(struct arch_timer_context *ctxt)
 {
-	if (ctxt->offset.vm_offset)
+	if (ctxt && ctxt->offset.vm_offset)
 		return *ctxt->offset.vm_offset;
 
 	return 0;
···
 	kvm_call_hyp(__kvm_timer_set_cntvoff, cntvoff);
 }
 
+static void set_cntpoff(u64 cntpoff)
+{
+	if (has_cntpoff())
+		write_sysreg_s(cntpoff, SYS_CNTPOFF_EL2);
+}
+
 static void timer_save_state(struct arch_timer_context *ctx)
 {
 	struct arch_timer_cpu *timer = vcpu_timer(ctx->vcpu);
···
 		write_sysreg_el0(0, SYS_CNTP_CTL);
 		isb();
 
+		set_cntpoff(0);
 		break;
 	case NR_KVM_TIMERS:
 		BUG();
···
 		write_sysreg_el0(timer_get_ctl(ctx), SYS_CNTV_CTL);
 		break;
 	case TIMER_PTIMER:
+		set_cntpoff(timer_get_offset(ctx));
 		write_sysreg_el0(timer_get_cval(ctx), SYS_CNTP_CVAL);
 		isb();
 		write_sysreg_el0(timer_get_ctl(ctx), SYS_CNTP_CTL);
···
 	vtimer->vcpu = vcpu;
 	vtimer->offset.vm_offset = &vcpu->kvm->arch.timer_data.voffset;
 	ptimer->vcpu = vcpu;
+	ptimer->offset.vm_offset = &vcpu->kvm->arch.timer_data.poffset;
 
 	/* Synchronize cntvoff across all vtimers of a VM. */
 	timer_set_offset(vtimer, kvm_phys_timer_read());
···
 	val = read_sysreg(cnthctl_el2);
 	val |= (CNTHCTL_EL1PCEN << cnthctl_shift);
 	val |= (CNTHCTL_EL1PCTEN << cnthctl_shift);
+	if (cpus_have_final_cap(ARM64_HAS_ECV_CNTPOFF))
+		val |= CNTHCTL_ECV;
 	write_sysreg(val, cnthctl_el2);
 }
 

arch/arm64/kvm/hypercalls.c

···
 		cycles = systime_snapshot.cycles - vcpu->kvm->arch.timer_data.voffset;
 		break;
 	case KVM_PTP_PHYS_COUNTER:
-		cycles = systime_snapshot.cycles;
+		cycles = systime_snapshot.cycles - vcpu->kvm->arch.timer_data.poffset;
 		break;
 	default:
 		return;

include/clocksource/arm_arch_timer.h

···
 #define CNTHCTL_EVNTEN			(1 << 2)
 #define CNTHCTL_EVNTDIR			(1 << 3)
 #define CNTHCTL_EVNTI			(0xF << 4)
+#define CNTHCTL_ECV			(1 << 12)
 
 enum arch_timer_reg {
 	ARCH_TIMER_REG_CTRL,

include/kvm/arm_arch_timer.h

···
 struct arch_timer_vm_data {
 	/* Offset applied to the virtual timer/counter */
 	u64	voffset;
+	/* Offset applied to the physical timer/counter */
+	u64	poffset;
 };
 
 struct arch_timer_context {