KVM: arm/arm64: vgic: Defer touching GICH_VMCR to vcpu_load/put

We don't have to save/restore the VMCR on every entry to/from the guest,
since on GICv2 we can access the control interface from EL1 and on VHE
systems with GICv3 we can access the control interface from KVM running
in EL2.

GICv3 systems without VHE becomes the rare case, which has to
save/restore the register on each round trip.

Note that userspace accesses may see out-of-date values if the VCPU is
running while accessing the VGIC state via the KVM device API, but this
is already the case and it is up to userspace to quiesce the CPUs before
reading the CPU registers from the GIC for an up-to-date view.

Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@cs.columbia.edu>
Signed-off-by: Christoffer Dall <cdall@linaro.org>

arch/arm/kvm/arm.c

@@ -351,15 +351,14 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	vcpu->arch.host_cpu_context = this_cpu_ptr(kvm_host_cpu_state);
 
 	kvm_arm_set_running_vcpu(vcpu);
+
+	kvm_vgic_load(vcpu);
 }
 
 void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 {
-	/*
-	 * The arch-generic KVM code expects the cpu field of a vcpu to be -1
-	 * if the vcpu is no longer assigned to a cpu.  This is used for the
-	 * optimized make_all_cpus_request path.
-	 */
+	kvm_vgic_put(vcpu);
+
 	vcpu->cpu = -1;
 
 	kvm_arm_set_running_vcpu(NULL);
@@ -633,7 +632,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
 		 * non-preemptible context.
 		 */
 		preempt_disable();
+
 		kvm_pmu_flush_hwstate(vcpu);
+
 		kvm_timer_flush_hwstate(vcpu);
 		kvm_vgic_flush_hwstate(vcpu);