KVM: arm64: nv: Publish emulated timer interrupt state in the in-memory state

With FEAT_NV2, the EL0 timer state is entirely stored in memory,
meaning that the hypervisor can only provide a very poor emulation.

The only thing we can really do is to publish the interrupt state
in the guest view of CNT{P,V}_CTL_EL0, and defer everything else
to the next exit.

Only FEAT_ECV will allow us to fix it, at the cost of extra trapping.

Suggested-by: Chase Conklin <[email protected]>
Suggested-by: Ganapatrao Kulkarni <[email protected]>
Acked-by: Oliver Upton <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Marc Zyngier <[email protected]>

Author: Marc Zyngier

arch/arm64/kvm/arch_timer.c

@@ -441,11 +441,30 @@ void kvm_timer_update_run(struct kvm_vcpu *vcpu)
 		regs->device_irq_level |= KVM_ARM_DEV_EL1_PTIMER;
 }
 
+static void kvm_timer_update_status(struct arch_timer_context *ctx, bool level)
+{
+	/*
+	 * Paper over NV2 brokenness by publishing the interrupt status
+	 * bit. This still results in a poor quality of emulation (guest
+	 * writes will have no effect until the next exit).
+	 *
+	 * But hey, it's fast, right?
+	 */
+	if (is_hyp_ctxt(ctx->vcpu) &&
+	    (ctx == vcpu_vtimer(ctx->vcpu) || ctx == vcpu_ptimer(ctx->vcpu))) {
+		unsigned long val = timer_get_ctl(ctx);
+		__assign_bit(__ffs(ARCH_TIMER_CTRL_IT_STAT), &val, level);
+		timer_set_ctl(ctx, val);
+	}
+}
+
 static void kvm_timer_update_irq(struct kvm_vcpu *vcpu, bool new_level,
 				 struct arch_timer_context *timer_ctx)
 {
 	int ret;
 
+	kvm_timer_update_status(timer_ctx, new_level);
+
 	timer_ctx->irq.level = new_level;
 	trace_kvm_timer_update_irq(vcpu->vcpu_id, timer_irq(timer_ctx),
 				   timer_ctx->irq.level);
@@ -471,6 +490,8 @@ static void timer_emulate(struct arch_timer_context *ctx)
 		return;
 	}
 
+	kvm_timer_update_status(ctx, should_fire);
+
 	/*
 	 * If the timer can fire now, we don't need to have a soft timer
 	 * scheduled for the future.  If the timer cannot fire at all,

arch/arm64/kvm/arm.c

@@ -1228,7 +1228,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 		if (unlikely(!irqchip_in_kernel(vcpu->kvm)))
 			kvm_timer_sync_user(vcpu);
 
-		if (vcpu_has_nv(vcpu))
+		if (is_hyp_ctxt(vcpu))
 			kvm_timer_sync_nested(vcpu);
 
 		kvm_arch_vcpu_ctxsync_fp(vcpu);