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Note that userspace accesses may see out-of-date values if the VCPU is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/include/asm/kvm_asm.h

@@ -75,7 +75,10 @@ extern void __init_stage2_translation(void);
 extern void __kvm_hyp_reset(unsigned long);
 
 extern u64 __vgic_v3_get_ich_vtr_el2(void);
+extern u64 __vgic_v3_read_vmcr(void);
+extern void __vgic_v3_write_vmcr(u32 vmcr);
 extern void __vgic_v3_init_lrs(void);
+
 #endif
 
 #endif /* __ARM_KVM_ASM_H__ */

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);
 

arch/arm64/include/asm/kvm_asm.h

@@ -59,6 +59,8 @@ extern void __kvm_tlb_flush_local_vmid(struct kvm_vcpu *vcpu);
 extern int __kvm_vcpu_run(struct kvm_vcpu *vcpu);
 
 extern u64 __vgic_v3_get_ich_vtr_el2(void);
+extern u64 __vgic_v3_read_vmcr(void);
+extern void __vgic_v3_write_vmcr(u32 vmcr);
 extern void __vgic_v3_init_lrs(void);
 
 extern u32 __kvm_get_mdcr_el2(void);

include/kvm/arm_vgic.h

@@ -306,6 +306,9 @@ bool kvm_vgic_map_is_active(struct kvm_vcpu *vcpu, unsigned int virt_irq);
 
 int kvm_vgic_vcpu_pending_irq(struct kvm_vcpu *vcpu);
 
+void kvm_vgic_load(struct kvm_vcpu *vcpu);
+void kvm_vgic_put(struct kvm_vcpu *vcpu);
+
 #define irqchip_in_kernel(k)	(!!((k)->arch.vgic.in_kernel))
 #define vgic_initialized(k)	((k)->arch.vgic.initialized)
 #define vgic_ready(k)		((k)->arch.vgic.ready)

virt/kvm/arm/hyp/vgic-v2-sr.c

@@ -114,8 +114,6 @@ void __hyp_text __vgic_v2_save_state(struct kvm_vcpu *vcpu)
 	if (!base)
 		return;
 
-	cpu_if->vgic_vmcr = readl_relaxed(base + GICH_VMCR);
-
 	if (vcpu->arch.vgic_cpu.live_lrs) {
 		cpu_if->vgic_apr = readl_relaxed(base + GICH_APR);
 
@@ -165,7 +163,6 @@ void __hyp_text __vgic_v2_restore_state(struct kvm_vcpu *vcpu)
 		}
 	}
 
-	writel_relaxed(cpu_if->vgic_vmcr, base + GICH_VMCR);
 	vcpu->arch.vgic_cpu.live_lrs = live_lrs;
 }
 

virt/kvm/arm/hyp/vgic-v3-sr.c

@@ -159,8 +159,6 @@ void __hyp_text __vgic_v3_save_state(struct kvm_vcpu *vcpu)
 	if (!cpu_if->vgic_sre)
 		dsb(st);
 
-	cpu_if->vgic_vmcr  = read_gicreg(ICH_VMCR_EL2);
-
 	if (vcpu->arch.vgic_cpu.live_lrs) {
 		int i;
 		u32 max_lr_idx, nr_pri_bits;
@@ -261,8 +259,6 @@ void __hyp_text __vgic_v3_restore_state(struct kvm_vcpu *vcpu)
 			live_lrs |= (1 << i);
 	}
 
-	write_gicreg(cpu_if->vgic_vmcr, ICH_VMCR_EL2);
-
 	if (live_lrs) {
 		write_gicreg(cpu_if->vgic_hcr, ICH_HCR_EL2);
 
@@ -326,3 +322,13 @@ u64 __hyp_text __vgic_v3_get_ich_vtr_el2(void)
 {
 	return read_gicreg(ICH_VTR_EL2);
 }
+
+u64 __hyp_text __vgic_v3_read_vmcr(void)
+{
+	return read_gicreg(ICH_VMCR_EL2);
+}
+
+void __hyp_text __vgic_v3_write_vmcr(u32 vmcr)
+{
+	write_gicreg(vmcr, ICH_VMCR_EL2);
+}

virt/kvm/arm/vgic/vgic-init.c

@@ -262,6 +262,18 @@ int vgic_init(struct kvm *kvm)
 	vgic_debug_init(kvm);
 
 	dist->initialized = true;
+
+	/*
+	 * If we're initializing GICv2 on-demand when first running the VCPU
+	 * then we need to load the VGIC state onto the CPU.  We can detect
+	 * this easily by checking if we are in between vcpu_load and vcpu_put
+	 * when we just initialized the VGIC.
+	 */
+	preempt_disable();
+	vcpu = kvm_arm_get_running_vcpu();
+	if (vcpu)
+		kvm_vgic_load(vcpu);
+	preempt_enable();
 out:
 	return ret;
 }

virt/kvm/arm/vgic/vgic-v2.c

@@ -184,6 +184,7 @@ void vgic_v2_clear_lr(struct kvm_vcpu *vcpu, int lr)
 
 void vgic_v2_set_vmcr(struct kvm_vcpu *vcpu, struct vgic_vmcr *vmcrp)
 {
+	struct vgic_v2_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v2;
 	u32 vmcr;
 
 	vmcr  = (vmcrp->ctlr << GICH_VMCR_CTRL_SHIFT) & GICH_VMCR_CTRL_MASK;
@@ -194,12 +195,15 @@ void vgic_v2_set_vmcr(struct kvm_vcpu *vcpu, struct vgic_vmcr *vmcrp)
 	vmcr |= (vmcrp->pmr << GICH_VMCR_PRIMASK_SHIFT) &
 		GICH_VMCR_PRIMASK_MASK;
 
-	vcpu->arch.vgic_cpu.vgic_v2.vgic_vmcr = vmcr;
+	cpu_if->vgic_vmcr = vmcr;
 }
 
 void vgic_v2_get_vmcr(struct kvm_vcpu *vcpu, struct vgic_vmcr *vmcrp)
 {
-	u32 vmcr = vcpu->arch.vgic_cpu.vgic_v2.vgic_vmcr;
+	struct vgic_v2_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v2;
+	u32 vmcr;
+
+	vmcr = cpu_if->vgic_vmcr;
 
 	vmcrp->ctlr = (vmcr & GICH_VMCR_CTRL_MASK) >>
 			GICH_VMCR_CTRL_SHIFT;
@@ -375,3 +379,19 @@ out:
 
 	return ret;
 }
+
+void vgic_v2_load(struct kvm_vcpu *vcpu)
+{
+	struct vgic_v2_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v2;
+	struct vgic_dist *vgic = &vcpu->kvm->arch.vgic;
+
+	writel_relaxed(cpu_if->vgic_vmcr, vgic->vctrl_base + GICH_VMCR);
+}
+
+void vgic_v2_put(struct kvm_vcpu *vcpu)
+{
+	struct vgic_v2_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v2;
+	struct vgic_dist *vgic = &vcpu->kvm->arch.vgic;
+
+	cpu_if->vgic_vmcr = readl_relaxed(vgic->vctrl_base + GICH_VMCR);
+}

virt/kvm/arm/vgic/vgic-v3.c

@@ -173,6 +173,7 @@ void vgic_v3_clear_lr(struct kvm_vcpu *vcpu, int lr)
 
 void vgic_v3_set_vmcr(struct kvm_vcpu *vcpu, struct vgic_vmcr *vmcrp)
 {
+	struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
 	u32 vmcr;
 
 	/*
@@ -188,12 +189,15 @@ void vgic_v3_set_vmcr(struct kvm_vcpu *vcpu, struct vgic_vmcr *vmcrp)
 	vmcr |= (vmcrp->grpen0 << ICH_VMCR_ENG0_SHIFT) & ICH_VMCR_ENG0_MASK;
 	vmcr |= (vmcrp->grpen1 << ICH_VMCR_ENG1_SHIFT) & ICH_VMCR_ENG1_MASK;
 
-	vcpu->arch.vgic_cpu.vgic_v3.vgic_vmcr = vmcr;
+	cpu_if->vgic_vmcr = vmcr;
 }
 
 void vgic_v3_get_vmcr(struct kvm_vcpu *vcpu, struct vgic_vmcr *vmcrp)
 {
-	u32 vmcr = vcpu->arch.vgic_cpu.vgic_v3.vgic_vmcr;
+	struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
+	u32 vmcr;
+
+	vmcr = cpu_if->vgic_vmcr;
 
 	/*
 	 * Ignore the FIQen bit, because GIC emulation always implies
@@ -386,3 +390,17 @@ int vgic_v3_probe(const struct gic_kvm_info *info)
 
 	return 0;
 }
+
+void vgic_v3_load(struct kvm_vcpu *vcpu)
+{
+	struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
+
+	kvm_call_hyp(__vgic_v3_write_vmcr, cpu_if->vgic_vmcr);
+}
+
+void vgic_v3_put(struct kvm_vcpu *vcpu)
+{
+	struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
+
+	cpu_if->vgic_vmcr = kvm_call_hyp(__vgic_v3_read_vmcr);
+}

virt/kvm/arm/vgic/vgic.c

@@ -656,6 +656,28 @@ void kvm_vgic_flush_hwstate(struct kvm_vcpu *vcpu)
 	spin_unlock(&vcpu->arch.vgic_cpu.ap_list_lock);
 }
 
+void kvm_vgic_load(struct kvm_vcpu *vcpu)
+{
+	if (unlikely(!vgic_initialized(vcpu->kvm)))
+		return;
+
+	if (kvm_vgic_global_state.type == VGIC_V2)
+		vgic_v2_load(vcpu);
+	else
+		vgic_v3_load(vcpu);
+}
+
+void kvm_vgic_put(struct kvm_vcpu *vcpu)
+{
+	if (unlikely(!vgic_initialized(vcpu->kvm)))
+		return;
+
+	if (kvm_vgic_global_state.type == VGIC_V2)
+		vgic_v2_put(vcpu);
+	else
+		vgic_v3_put(vcpu);
+}
+
 int kvm_vgic_vcpu_pending_irq(struct kvm_vcpu *vcpu)
 {
 	struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;

virt/kvm/arm/vgic/vgic.h

@@ -130,6 +130,9 @@ int vgic_v2_map_resources(struct kvm *kvm);
 int vgic_register_dist_iodev(struct kvm *kvm, gpa_t dist_base_address,
 			     enum vgic_type);
 
+void vgic_v2_load(struct kvm_vcpu *vcpu);
+void vgic_v2_put(struct kvm_vcpu *vcpu);
+
 static inline void vgic_get_irq_kref(struct vgic_irq *irq)
 {
 	if (irq->intid < VGIC_MIN_LPI)
@@ -150,6 +153,9 @@ int vgic_v3_probe(const struct gic_kvm_info *info);
 int vgic_v3_map_resources(struct kvm *kvm);
 int vgic_register_redist_iodevs(struct kvm *kvm, gpa_t dist_base_address);
 
+void vgic_v3_load(struct kvm_vcpu *vcpu);
+void vgic_v3_put(struct kvm_vcpu *vcpu);
+
 int vgic_register_its_iodevs(struct kvm *kvm);
 bool vgic_has_its(struct kvm *kvm);
 int kvm_vgic_register_its_device(void);