arm64: KVM: vgic-v3: Save maintenance interrupt state only if required

Next on our list of useless accesses is the maintenance interrupt
status registers (ICH_MISR_EL2, ICH_EISR_EL2).

It is pointless to save them if we haven't asked for a maintenance
interrupt the first place, which can only happen for two reasons:
- Underflow: ICH_HCR_UIE will be set,
- EOI: ICH_LR_EOI will be set.

These conditions can be checked on the in-memory copies of the regs.
Should any of these two condition be valid, we must read GICH_MISR.
We can then check for ICH_MISR_EOI, and only when set read
ICH_EISR_EL2.

This means that in most case, we don't have to save them at all.
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm64/kvm/hyp/vgic-v3-sr.c

@@ -131,6 +131,35 @@ static void __hyp_text __gic_v3_set_lr(u64 val, int lr)
 	}
 }
 
+static void __hyp_text save_maint_int_state(struct kvm_vcpu *vcpu, int nr_lr)
+{
+	struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
+	int i;
+	bool expect_mi;
+
+	expect_mi = !!(cpu_if->vgic_hcr & ICH_HCR_UIE);
+
+	for (i = 0; i < nr_lr; i++) {
+		if (!(vcpu->arch.vgic_cpu.live_lrs & (1UL << i)))
+				continue;
+
+		expect_mi |= (!(cpu_if->vgic_lr[i] & ICH_LR_HW) &&
+			      (cpu_if->vgic_lr[i] & ICH_LR_EOI));
+	}
+
+	if (expect_mi) {
+		cpu_if->vgic_misr  = read_gicreg(ICH_MISR_EL2);
+
+		if (cpu_if->vgic_misr & ICH_MISR_EOI)
+			cpu_if->vgic_eisr = read_gicreg(ICH_EISR_EL2);
+		else
+			cpu_if->vgic_eisr = 0;
+	} else {
+		cpu_if->vgic_misr = 0;
+		cpu_if->vgic_eisr = 0;
+	}
+}
+
 void __hyp_text __vgic_v3_save_state(struct kvm_vcpu *vcpu)
 {
 	struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
@@ -148,8 +177,6 @@ void __hyp_text __vgic_v3_save_state(struct kvm_vcpu *vcpu)
 		int i;
 		u32 max_lr_idx, nr_pri_bits;
 
-		cpu_if->vgic_misr  = read_gicreg(ICH_MISR_EL2);
-		cpu_if->vgic_eisr  = read_gicreg(ICH_EISR_EL2);
 		cpu_if->vgic_elrsr = read_gicreg(ICH_ELSR_EL2);
 
 		write_gicreg(0, ICH_HCR_EL2);
@@ -157,6 +184,8 @@ void __hyp_text __vgic_v3_save_state(struct kvm_vcpu *vcpu)
 		max_lr_idx = vtr_to_max_lr_idx(val);
 		nr_pri_bits = vtr_to_nr_pri_bits(val);
 
+		save_maint_int_state(vcpu, max_lr_idx + 1);
+
 		for (i = 0; i <= max_lr_idx; i++) {
 			if (vcpu->arch.vgic_cpu.live_lrs & (1UL << i))
 				cpu_if->vgic_lr[i] = __gic_v3_get_lr(i);