[PATCH v7 62/68] KVM: arm64: nv: Publish emulated timer interrupt state in the in-memory state

[Marc Zyngier]

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 <chase.conklin at arm.com>
Suggested-by: Ganapatrao Kulkarni <gankulkarni at os.amperecomputing.com>
Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/kvm/arch_timer.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
index c01277e8bd4a..71d2f1902de9 100644
--- a/arch/arm64/kvm/arch_timer.c
+++ b/arch/arm64/kvm/arch_timer.c
@@ -450,6 +450,25 @@ static void kvm_timer_update_irq(struct kvm_vcpu *vcpu, bool new_level,
 {
 	int ret;
 
+	/*
+	 * 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 (vcpu_has_nv2(vcpu) && is_hyp_ctxt(vcpu) &&
+	    (timer_ctx == vcpu_vtimer(vcpu) || timer_ctx == vcpu_ptimer(vcpu))) {
+		u32 ctl = timer_get_ctl(timer_ctx);
+
+		if (new_level)
+			ctl |= ARCH_TIMER_CTRL_IT_STAT;
+		else
+			ctl &= ~ARCH_TIMER_CTRL_IT_STAT;
+
+		timer_set_ctl(timer_ctx, ctl);
+	}
+
 	timer_ctx->irq.level = new_level;
 	trace_kvm_timer_update_irq(vcpu->vcpu_id, timer_ctx->irq.irq,
 				   timer_ctx->irq.level);
-- 
2.34.1