KVM: arm/arm64: vgic-new: Export register access interface

Userland can access the emulated GIC to save and restore its state
for initialization or migration purposes.
The kvm_io_bus API requires an absolute gpa, which does not fit the
KVM_DEV_ARM_VGIC_GRP_DIST_REGS user API, that only provides relative
offsets. So we provide a wrapper to plug into our MMIO framework and
find the respective register handler.
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>

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

@@ -296,3 +296,39 @@ int vgic_v2_has_attr_regs(struct kvm_device *dev, struct kvm_device_attr *attr)
 
 	return -ENXIO;
 }
+
+/*
+ * When userland tries to access the VGIC register handlers, we need to
+ * create a usable struct vgic_io_device to be passed to the handlers and we
+ * have to set up a buffer similar to what would have happened if a guest MMIO
+ * access occurred, including doing endian conversions on BE systems.
+ */
+static int vgic_uaccess(struct kvm_vcpu *vcpu, struct vgic_io_device *dev,
+			bool is_write, int offset, u32 *val)
+{
+	unsigned int len = 4;
+	u8 buf[4];
+	int ret;
+
+	if (is_write) {
+		vgic_data_host_to_mmio_bus(buf, len, *val);
+		ret = kvm_io_gic_ops.write(vcpu, &dev->dev, offset, len, buf);
+	} else {
+		ret = kvm_io_gic_ops.read(vcpu, &dev->dev, offset, len, buf);
+		if (!ret)
+			*val = vgic_data_mmio_bus_to_host(buf, len);
+	}
+
+	return ret;
+}
+
+int vgic_v2_dist_uaccess(struct kvm_vcpu *vcpu, bool is_write,
+			 int offset, u32 *val)
+{
+	struct vgic_io_device dev = {
+		.regions = vgic_v2_dist_registers,
+		.nr_regions = ARRAY_SIZE(vgic_v2_dist_registers),
+	};
+
+	return vgic_uaccess(vcpu, &dev, is_write, offset, val);
+}

virt/kvm/arm/vgic/vgic.h

@@ -38,6 +38,8 @@ void vgic_v2_populate_lr(struct kvm_vcpu *vcpu, struct vgic_irq *irq, int lr);
 void vgic_v2_clear_lr(struct kvm_vcpu *vcpu, int lr);
 void vgic_v2_set_underflow(struct kvm_vcpu *vcpu);
 int vgic_v2_has_attr_regs(struct kvm_device *dev, struct kvm_device_attr *attr);
+int vgic_v2_dist_uaccess(struct kvm_vcpu *vcpu, bool is_write,
+			 int offset, u32 *val);
 int vgic_register_dist_iodev(struct kvm *kvm, gpa_t dist_base_address,
 			     enum vgic_type);