drivers/s390/kvm/kvm_virtio.c - kernel/mindspeed - Git at Google

 /*
  * kvm_virtio.c - virtio for kvm on s390
  *
  * Copyright IBM Corp. 2008
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License (version 2 only)
  * as published by the Free Software Foundation.
  *
  *    Author(s): Christian Borntraeger <borntraeger@de.ibm.com>
  */

 #include <linux/kernel_stat.h>
 #include <linux/init.h>
 #include <linux/bootmem.h>
 #include <linux/err.h>
 #include <linux/virtio.h>
 #include <linux/virtio_config.h>
 #include <linux/slab.h>
 #include <linux/virtio_console.h>
 #include <linux/interrupt.h>
 #include <linux/virtio_ring.h>
 #include <linux/export.h>
 #include <linux/pfn.h>
 #include <asm/io.h>
 #include <asm/kvm_para.h>
 #include <asm/kvm_virtio.h>
 #include <asm/setup.h>
 #include <asm/irq.h>

 #define VIRTIO_SUBCODE_64 0x0D00

 /*
  * The pointer to our (page) of device descriptions.
  */
 static void *kvm_devices;
 static struct work_struct hotplug_work;

 struct kvm_device {
 	struct virtio_device vdev;
 	struct kvm_device_desc *desc;
 };

 #define to_kvmdev(vd) container_of(vd, struct kvm_device, vdev)

 /*
  * memory layout:
  * - kvm_device_descriptor
  *        struct kvm_device_desc
  * - configuration
  *        struct kvm_vqconfig
  * - feature bits
  * - config space
  */
 static struct kvm_vqconfig *kvm_vq_config(const struct kvm_device_desc *desc)
 {
 	return (struct kvm_vqconfig *)(desc + 1);
 }

 static u8 *kvm_vq_features(const struct kvm_device_desc *desc)
 {
 	return (u8 *)(kvm_vq_config(desc) + desc->num_vq);
 }

 static u8 *kvm_vq_configspace(const struct kvm_device_desc *desc)
 {
 	return kvm_vq_features(desc) + desc->feature_len * 2;
 }

 /*
  * The total size of the config page used by this device (incl. desc)
  */
 static unsigned desc_size(const struct kvm_device_desc *desc)
 {
 	return sizeof(*desc)
 		+ desc->num_vq * sizeof(struct kvm_vqconfig)
 		+ desc->feature_len * 2
 		+ desc->config_len;
 }

 /* This gets the device's feature bits. */
 static u32 kvm_get_features(struct virtio_device *vdev)
 {
 	unsigned int i;
 	u32 features = 0;
 	struct kvm_device_desc *desc = to_kvmdev(vdev)->desc;
 	u8 *in_features = kvm_vq_features(desc);

 	for (i = 0; i < min(desc->feature_len * 8, 32); i++)
 		if (in_features[i / 8] & (1 << (i % 8)))
 			features |= (1 << i);
 	return features;
 }

 static void kvm_finalize_features(struct virtio_device *vdev)
 {
 	unsigned int i, bits;
 	struct kvm_device_desc *desc = to_kvmdev(vdev)->desc;
 	/* Second half of bitmap is features we accept. */
 	u8 *out_features = kvm_vq_features(desc) + desc->feature_len;

 	/* Give virtio_ring a chance to accept features. */
 	vring_transport_features(vdev);

 	memset(out_features, 0, desc->feature_len);
 	bits = min_t(unsigned, desc->feature_len, sizeof(vdev->features)) * 8;
 	for (i = 0; i < bits; i++) {
 		if (test_bit(i, vdev->features))
 			out_features[i / 8] |= (1 << (i % 8));
 	}
 }

 /*
  * Reading and writing elements in config space
  */
 static void kvm_get(struct virtio_device *vdev, unsigned int offset,
 		   void *buf, unsigned len)
 {
 	struct kvm_device_desc *desc = to_kvmdev(vdev)->desc;

 	BUG_ON(offset + len > desc->config_len);
 	memcpy(buf, kvm_vq_configspace(desc) + offset, len);
 }

 static void kvm_set(struct virtio_device *vdev, unsigned int offset,
 		   const void *buf, unsigned len)
 {
 	struct kvm_device_desc *desc = to_kvmdev(vdev)->desc;

 	BUG_ON(offset + len > desc->config_len);
 	memcpy(kvm_vq_configspace(desc) + offset, buf, len);
 }

 /*
  * The operations to get and set the status word just access
  * the status field of the device descriptor. set_status will also
  * make a hypercall to the host, to tell about status changes
  */
 static u8 kvm_get_status(struct virtio_device *vdev)
 {
 	return to_kvmdev(vdev)->desc->status;
 }

 static void kvm_set_status(struct virtio_device *vdev, u8 status)
 {
 	BUG_ON(!status);
 	to_kvmdev(vdev)->desc->status = status;
 	kvm_hypercall1(KVM_S390_VIRTIO_SET_STATUS,
 		       (unsigned long) to_kvmdev(vdev)->desc);
 }

 /*
  * To reset the device, we use the KVM_VIRTIO_RESET hypercall, using the
  * descriptor address. The Host will zero the status and all the
  * features.
  */
 static void kvm_reset(struct virtio_device *vdev)
 {
 	kvm_hypercall1(KVM_S390_VIRTIO_RESET,
 		       (unsigned long) to_kvmdev(vdev)->desc);
 }

 /*
  * When the virtio_ring code wants to notify the Host, it calls us here and we
  * make a hypercall.  We hand the address  of the virtqueue so the Host
  * knows which virtqueue we're talking about.
  */
 static void kvm_notify(struct virtqueue *vq)
 {
 	struct kvm_vqconfig *config = vq->priv;

 	kvm_hypercall1(KVM_S390_VIRTIO_NOTIFY, config->address);
 }

 /*
  * This routine finds the first virtqueue described in the configuration of
  * this device and sets it up.
  */
 static struct virtqueue *kvm_find_vq(struct virtio_device *vdev,
 				     unsigned index,
 				     void (*callback)(struct virtqueue *vq),
 				     const char *name)
 {
 	struct kvm_device *kdev = to_kvmdev(vdev);
 	struct kvm_vqconfig *config;
 	struct virtqueue *vq;
 	int err;

 	if (index >= kdev->desc->num_vq)
 		return ERR_PTR(-ENOENT);

 	config = kvm_vq_config(kdev->desc)+index;

 	err = vmem_add_mapping(config->address,
 			       vring_size(config->num,
 					  KVM_S390_VIRTIO_RING_ALIGN));
 	if (err)
 		goto out;

 	vq = vring_new_virtqueue(config->num, KVM_S390_VIRTIO_RING_ALIGN,
 				 vdev, (void *) config->address,
 				 kvm_notify, callback, name);
 	if (!vq) {
 		err = -ENOMEM;
 		goto unmap;
 	}

 	/*
 	 * register a callback token
 	 * The host will sent this via the external interrupt parameter
 	 */
 	config->token = (u64) vq;

 	vq->priv = config;
 	return vq;
 unmap:
 	vmem_remove_mapping(config->address,
 			    vring_size(config->num,
 				       KVM_S390_VIRTIO_RING_ALIGN));
 out:
 	return ERR_PTR(err);
 }

 static void kvm_del_vq(struct virtqueue *vq)
 {
 	struct kvm_vqconfig *config = vq->priv;

 	vring_del_virtqueue(vq);
 	vmem_remove_mapping(config->address,
 			    vring_size(config->num,
 				       KVM_S390_VIRTIO_RING_ALIGN));
 }

 static void kvm_del_vqs(struct virtio_device *vdev)
 {
 	struct virtqueue *vq, *n;

 	list_for_each_entry_safe(vq, n, &vdev->vqs, list)
 		kvm_del_vq(vq);
 }

 static int kvm_find_vqs(struct virtio_device *vdev, unsigned nvqs,
 			struct virtqueue *vqs[],
 			vq_callback_t *callbacks[],
 			const char *names[])
 {
 	struct kvm_device *kdev = to_kvmdev(vdev);
 	int i;

 	/* We must have this many virtqueues. */
 	if (nvqs > kdev->desc->num_vq)
 		return -ENOENT;

 	for (i = 0; i < nvqs; ++i) {
 		vqs[i] = kvm_find_vq(vdev, i, callbacks[i], names[i]);
 		if (IS_ERR(vqs[i]))
 			goto error;
 	}
 	return 0;

 error:
 	kvm_del_vqs(vdev);
 	return PTR_ERR(vqs[i]);
 }

 /*
  * The config ops structure as defined by virtio config
  */
 static struct virtio_config_ops kvm_vq_configspace_ops = {
 	.get_features = kvm_get_features,
 	.finalize_features = kvm_finalize_features,
 	.get = kvm_get,
 	.set = kvm_set,
 	.get_status = kvm_get_status,
 	.set_status = kvm_set_status,
 	.reset = kvm_reset,
 	.find_vqs = kvm_find_vqs,
 	.del_vqs = kvm_del_vqs,
 };

 /*
  * The root device for the kvm virtio devices.
  * This makes them appear as /sys/devices/kvm_s390/0,1,2 not /sys/devices/0,1,2.
  */
 static struct device *kvm_root;

 /*
  * adds a new device and register it with virtio
  * appropriate drivers are loaded by the device model
  */
 static void add_kvm_device(struct kvm_device_desc *d, unsigned int offset)
 {
 	struct kvm_device *kdev;

 	kdev = kzalloc(sizeof(*kdev), GFP_KERNEL);
 	if (!kdev) {
 		printk(KERN_EMERG "Cannot allocate kvm dev %u type %u\n",
 		       offset, d->type);
 		return;
 	}

 	kdev->vdev.dev.parent = kvm_root;
 	kdev->vdev.id.device = d->type;
 	kdev->vdev.config = &kvm_vq_configspace_ops;
 	kdev->desc = d;

 	if (register_virtio_device(&kdev->vdev) != 0) {
 		printk(KERN_ERR "Failed to register kvm device %u type %u\n",
 		       offset, d->type);
 		kfree(kdev);
 	}
 }

 /*
  * scan_devices() simply iterates through the device page.
  * The type 0 is reserved to mean "end of devices".
  */
 static void scan_devices(void)
 {
 	unsigned int i;
 	struct kvm_device_desc *d;

 	for (i = 0; i < PAGE_SIZE; i += desc_size(d)) {
 		d = kvm_devices + i;

 		if (d->type == 0)
 			break;

 		add_kvm_device(d, i);
 	}
 }

 /*
  * match for a kvm device with a specific desc pointer
  */
 static int match_desc(struct device *dev, void *data)
 {
 	struct virtio_device *vdev = dev_to_virtio(dev);
 	struct kvm_device *kdev = to_kvmdev(vdev);

 	return kdev->desc == data;
 }

 /*
  * hotplug_device tries to find changes in the device page.
  */
 static void hotplug_devices(struct work_struct *dummy)
 {
 	unsigned int i;
 	struct kvm_device_desc *d;
 	struct device *dev;

 	for (i = 0; i < PAGE_SIZE; i += desc_size(d)) {
 		d = kvm_devices + i;

 		/* end of list */
 		if (d->type == 0)
 			break;

 		/* device already exists */
 		dev = device_find_child(kvm_root, d, match_desc);
 		if (dev) {
 			/* XXX check for hotplug remove */
 			put_device(dev);
 			continue;
 		}

 		/* new device */
 		printk(KERN_INFO "Adding new virtio device %p\n", d);
 		add_kvm_device(d, i);
 	}
 }

 /*
  * we emulate the request_irq behaviour on top of s390 extints
  */
 static void kvm_extint_handler(unsigned int ext_int_code,
 			       unsigned int param32, unsigned long param64)
 {
 	struct virtqueue *vq;
 	u16 subcode;
 	u32 param;

 	subcode = ext_int_code >> 16;
 	if ((subcode & 0xff00) != VIRTIO_SUBCODE_64)
 		return;
 	kstat_cpu(smp_processor_id()).irqs[EXTINT_VRT]++;

 	/* The LSB might be overloaded, we have to mask it */
 	vq = (struct virtqueue *)(param64 & ~1UL);

 	/* We use ext_params to decide what this interrupt means */
 	param = param32 & VIRTIO_PARAM_MASK;

 	switch (param) {
 	case VIRTIO_PARAM_CONFIG_CHANGED:
 	{
 		struct virtio_driver *drv;
 		drv = container_of(vq->vdev->dev.driver,
 				   struct virtio_driver, driver);
 		if (drv->config_changed)
 			drv->config_changed(vq->vdev);

 		break;
 	}
 	case VIRTIO_PARAM_DEV_ADD:
 		schedule_work(&hotplug_work);
 		break;
 	case VIRTIO_PARAM_VRING_INTERRUPT:
 	default:
 		vring_interrupt(0, vq);
 		break;
 	}
 }

 /*
  * Init function for virtio
  * devices are in a single page above top of "normal" mem
  */
 static int __init kvm_devices_init(void)
 {
 	int rc;

 	if (!MACHINE_IS_KVM)
 		return -ENODEV;

 	kvm_root = root_device_register("kvm_s390");
 	if (IS_ERR(kvm_root)) {
 		rc = PTR_ERR(kvm_root);
 		printk(KERN_ERR "Could not register kvm_s390 root device");
 		return rc;
 	}

 	rc = vmem_add_mapping(real_memory_size, PAGE_SIZE);
 	if (rc) {
 		root_device_unregister(kvm_root);
 		return rc;
 	}

 	kvm_devices = (void *) real_memory_size;

 	INIT_WORK(&hotplug_work, hotplug_devices);

 	service_subclass_irq_register();
 	register_external_interrupt(0x2603, kvm_extint_handler);

 	scan_devices();
 	return 0;
 }

 /* code for early console output with virtio_console */
 static __init int early_put_chars(u32 vtermno, const char *buf, int count)
 {
 	char scratch[17];
 	unsigned int len = count;

 	if (len > sizeof(scratch) - 1)
 		len = sizeof(scratch) - 1;
 	scratch[len] = '\0';
 	memcpy(scratch, buf, len);
 	kvm_hypercall1(KVM_S390_VIRTIO_NOTIFY, __pa(scratch));
 	return len;
 }

 static int __init s390_virtio_console_init(void)
 {
 	if (!MACHINE_IS_KVM)
 		return -ENODEV;
 	return virtio_cons_early_init(early_put_chars);
 }
 console_initcall(s390_virtio_console_init);


 /*
  * We do this after core stuff, but before the drivers.
  */
 postcore_initcall(kvm_devices_init);
	/*
	* kvm_virtio.c - virtio for kvm on s390
	*
	* Copyright IBM Corp. 2008
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License (version 2 only)
	* as published by the Free Software Foundation.
	*
	* Author(s): Christian Borntraeger <borntraeger@de.ibm.com>
	*/

	#include <linux/kernel_stat.h>
	#include <linux/init.h>
	#include <linux/bootmem.h>
	#include <linux/err.h>
	#include <linux/virtio.h>
	#include <linux/virtio_config.h>
	#include <linux/slab.h>
	#include <linux/virtio_console.h>
	#include <linux/interrupt.h>
	#include <linux/virtio_ring.h>
	#include <linux/export.h>
	#include <linux/pfn.h>
	#include <asm/io.h>
	#include <asm/kvm_para.h>
	#include <asm/kvm_virtio.h>
	#include <asm/setup.h>
	#include <asm/irq.h>

	#define VIRTIO_SUBCODE_64 0x0D00

	/*
	* The pointer to our (page) of device descriptions.
	*/
	static void *kvm_devices;
	static struct work_struct hotplug_work;

	struct kvm_device {
	struct virtio_device vdev;
	struct kvm_device_desc *desc;
	};

	#define to_kvmdev(vd) container_of(vd, struct kvm_device, vdev)

	/*
	* memory layout:
	* - kvm_device_descriptor
	* struct kvm_device_desc
	* - configuration
	* struct kvm_vqconfig
	* - feature bits
	* - config space
	*/
	static struct kvm_vqconfig kvm_vq_config(const struct kvm_device_desc desc)
	{
	return (struct kvm_vqconfig *)(desc + 1);
	}

	static u8 kvm_vq_features(const struct kvm_device_desc desc)
	{
	return (u8 *)(kvm_vq_config(desc) + desc->num_vq);
	}

	static u8 kvm_vq_configspace(const struct kvm_device_desc desc)
	{
	return kvm_vq_features(desc) + desc->feature_len * 2;
	}

	/*
	* The total size of the config page used by this device (incl. desc)
	*/
	static unsigned desc_size(const struct kvm_device_desc *desc)
	{
	return sizeof(*desc)
	+ desc->num_vq * sizeof(struct kvm_vqconfig)
	+ desc->feature_len * 2
	+ desc->config_len;
	}

	/* This gets the device's feature bits. */
	static u32 kvm_get_features(struct virtio_device *vdev)
	{
	unsigned int i;
	u32 features = 0;
	struct kvm_device_desc *desc = to_kvmdev(vdev)->desc;
	u8 *in_features = kvm_vq_features(desc);

	for (i = 0; i < min(desc->feature_len * 8, 32); i++)
	if (in_features[i / 8] & (1 << (i % 8)))
	features \|= (1 << i);
	return features;
	}

	static void kvm_finalize_features(struct virtio_device *vdev)
	{
	unsigned int i, bits;
	struct kvm_device_desc *desc = to_kvmdev(vdev)->desc;
	/* Second half of bitmap is features we accept. */
	u8 *out_features = kvm_vq_features(desc) + desc->feature_len;

	/* Give virtio_ring a chance to accept features. */
	vring_transport_features(vdev);

	memset(out_features, 0, desc->feature_len);
	bits = min_t(unsigned, desc->feature_len, sizeof(vdev->features)) * 8;
	for (i = 0; i < bits; i++) {
	if (test_bit(i, vdev->features))
	out_features[i / 8] \|= (1 << (i % 8));
	}
	}

	/*
	* Reading and writing elements in config space
	*/
	static void kvm_get(struct virtio_device *vdev, unsigned int offset,
	void *buf, unsigned len)
	{
	struct kvm_device_desc *desc = to_kvmdev(vdev)->desc;

	BUG_ON(offset + len > desc->config_len);
	memcpy(buf, kvm_vq_configspace(desc) + offset, len);
	}

	static void kvm_set(struct virtio_device *vdev, unsigned int offset,
	const void *buf, unsigned len)
	{
	struct kvm_device_desc *desc = to_kvmdev(vdev)->desc;

	BUG_ON(offset + len > desc->config_len);
	memcpy(kvm_vq_configspace(desc) + offset, buf, len);
	}

	/*
	* The operations to get and set the status word just access
	* the status field of the device descriptor. set_status will also
	* make a hypercall to the host, to tell about status changes
	*/
	static u8 kvm_get_status(struct virtio_device *vdev)
	{
	return to_kvmdev(vdev)->desc->status;
	}

	static void kvm_set_status(struct virtio_device *vdev, u8 status)
	{
	BUG_ON(!status);
	to_kvmdev(vdev)->desc->status = status;
	kvm_hypercall1(KVM_S390_VIRTIO_SET_STATUS,
	(unsigned long) to_kvmdev(vdev)->desc);
	}

	/*
	* To reset the device, we use the KVM_VIRTIO_RESET hypercall, using the
	* descriptor address. The Host will zero the status and all the
	* features.
	*/
	static void kvm_reset(struct virtio_device *vdev)
	{
	kvm_hypercall1(KVM_S390_VIRTIO_RESET,
	(unsigned long) to_kvmdev(vdev)->desc);
	}

	/*
	* When the virtio_ring code wants to notify the Host, it calls us here and we
	* make a hypercall. We hand the address of the virtqueue so the Host
	* knows which virtqueue we're talking about.
	*/
	static void kvm_notify(struct virtqueue *vq)
	{
	struct kvm_vqconfig *config = vq->priv;

	kvm_hypercall1(KVM_S390_VIRTIO_NOTIFY, config->address);
	}

	/*
	* This routine finds the first virtqueue described in the configuration of
	* this device and sets it up.
	*/
	static struct virtqueue kvm_find_vq(struct virtio_device vdev,
	unsigned index,
	void (callback)(struct virtqueue vq),
	const char *name)
	{
	struct kvm_device *kdev = to_kvmdev(vdev);
	struct kvm_vqconfig *config;
	struct virtqueue *vq;
	int err;

	if (index >= kdev->desc->num_vq)
	return ERR_PTR(-ENOENT);

	config = kvm_vq_config(kdev->desc)+index;

	err = vmem_add_mapping(config->address,
	vring_size(config->num,
	KVM_S390_VIRTIO_RING_ALIGN));
	if (err)
	goto out;

	vq = vring_new_virtqueue(config->num, KVM_S390_VIRTIO_RING_ALIGN,
	vdev, (void *) config->address,
	kvm_notify, callback, name);
	if (!vq) {
	err = -ENOMEM;
	goto unmap;
	}

	/*
	* register a callback token
	* The host will sent this via the external interrupt parameter
	*/
	config->token = (u64) vq;

	vq->priv = config;
	return vq;
	unmap:
	vmem_remove_mapping(config->address,
	vring_size(config->num,
	KVM_S390_VIRTIO_RING_ALIGN));
	out:
	return ERR_PTR(err);
	}

	static void kvm_del_vq(struct virtqueue *vq)
	{
	struct kvm_vqconfig *config = vq->priv;

	vring_del_virtqueue(vq);
	vmem_remove_mapping(config->address,
	vring_size(config->num,
	KVM_S390_VIRTIO_RING_ALIGN));
	}

	static void kvm_del_vqs(struct virtio_device *vdev)
	{
	struct virtqueue vq, n;

	list_for_each_entry_safe(vq, n, &vdev->vqs, list)
	kvm_del_vq(vq);
	}

	static int kvm_find_vqs(struct virtio_device *vdev, unsigned nvqs,
	struct virtqueue *vqs[],
	vq_callback_t *callbacks[],
	const char *names[])
	{
	struct kvm_device *kdev = to_kvmdev(vdev);
	int i;

	/* We must have this many virtqueues. */
	if (nvqs > kdev->desc->num_vq)
	return -ENOENT;

	for (i = 0; i < nvqs; ++i) {
	vqs[i] = kvm_find_vq(vdev, i, callbacks[i], names[i]);
	if (IS_ERR(vqs[i]))
	goto error;
	}
	return 0;

	error:
	kvm_del_vqs(vdev);
	return PTR_ERR(vqs[i]);
	}

	/*
	* The config ops structure as defined by virtio config
	*/
	static struct virtio_config_ops kvm_vq_configspace_ops = {
	.get_features = kvm_get_features,
	.finalize_features = kvm_finalize_features,
	.get = kvm_get,
	.set = kvm_set,
	.get_status = kvm_get_status,
	.set_status = kvm_set_status,
	.reset = kvm_reset,
	.find_vqs = kvm_find_vqs,
	.del_vqs = kvm_del_vqs,
	};

	/*
	* The root device for the kvm virtio devices.
	* This makes them appear as /sys/devices/kvm_s390/0,1,2 not /sys/devices/0,1,2.
	*/
	static struct device *kvm_root;

	/*
	* adds a new device and register it with virtio
	* appropriate drivers are loaded by the device model
	*/
	static void add_kvm_device(struct kvm_device_desc *d, unsigned int offset)
	{
	struct kvm_device *kdev;

	kdev = kzalloc(sizeof(*kdev), GFP_KERNEL);
	if (!kdev) {
	printk(KERN_EMERG "Cannot allocate kvm dev %u type %u\n",
	offset, d->type);
	return;
	}

	kdev->vdev.dev.parent = kvm_root;
	kdev->vdev.id.device = d->type;
	kdev->vdev.config = &kvm_vq_configspace_ops;
	kdev->desc = d;

	if (register_virtio_device(&kdev->vdev) != 0) {
	printk(KERN_ERR "Failed to register kvm device %u type %u\n",
	offset, d->type);
	kfree(kdev);
	}
	}

	/*
	* scan_devices() simply iterates through the device page.
	* The type 0 is reserved to mean "end of devices".
	*/
	static void scan_devices(void)
	{
	unsigned int i;
	struct kvm_device_desc *d;

	for (i = 0; i < PAGE_SIZE; i += desc_size(d)) {
	d = kvm_devices + i;

	if (d->type == 0)
	break;

	add_kvm_device(d, i);
	}
	}

	/*
	* match for a kvm device with a specific desc pointer
	*/
	static int match_desc(struct device dev, void data)
	{
	struct virtio_device *vdev = dev_to_virtio(dev);
	struct kvm_device *kdev = to_kvmdev(vdev);

	return kdev->desc == data;
	}

	/*
	* hotplug_device tries to find changes in the device page.
	*/
	static void hotplug_devices(struct work_struct *dummy)
	{
	unsigned int i;
	struct kvm_device_desc *d;
	struct device *dev;

	for (i = 0; i < PAGE_SIZE; i += desc_size(d)) {
	d = kvm_devices + i;

	/* end of list */
	if (d->type == 0)
	break;

	/* device already exists */
	dev = device_find_child(kvm_root, d, match_desc);
	if (dev) {
	/* XXX check for hotplug remove */
	put_device(dev);
	continue;
	}

	/* new device */
	printk(KERN_INFO "Adding new virtio device %p\n", d);
	add_kvm_device(d, i);
	}
	}

	/*
	* we emulate the request_irq behaviour on top of s390 extints
	*/
	static void kvm_extint_handler(unsigned int ext_int_code,
	unsigned int param32, unsigned long param64)
	{
	struct virtqueue *vq;
	u16 subcode;
	u32 param;

	subcode = ext_int_code >> 16;
	if ((subcode & 0xff00) != VIRTIO_SUBCODE_64)
	return;
	kstat_cpu(smp_processor_id()).irqs[EXTINT_VRT]++;

	/* The LSB might be overloaded, we have to mask it */
	vq = (struct virtqueue *)(param64 & ~1UL);

	/* We use ext_params to decide what this interrupt means */
	param = param32 & VIRTIO_PARAM_MASK;

	switch (param) {
	case VIRTIO_PARAM_CONFIG_CHANGED:
	{
	struct virtio_driver *drv;
	drv = container_of(vq->vdev->dev.driver,
	struct virtio_driver, driver);
	if (drv->config_changed)
	drv->config_changed(vq->vdev);

	break;
	}
	case VIRTIO_PARAM_DEV_ADD:
	schedule_work(&hotplug_work);
	break;
	case VIRTIO_PARAM_VRING_INTERRUPT:
	default:
	vring_interrupt(0, vq);
	break;
	}
	}

	/*
	* Init function for virtio
	* devices are in a single page above top of "normal" mem
	*/
	static int __init kvm_devices_init(void)
	{
	int rc;

	if (!MACHINE_IS_KVM)
	return -ENODEV;

	kvm_root = root_device_register("kvm_s390");
	if (IS_ERR(kvm_root)) {
	rc = PTR_ERR(kvm_root);
	printk(KERN_ERR "Could not register kvm_s390 root device");
	return rc;
	}

	rc = vmem_add_mapping(real_memory_size, PAGE_SIZE);
	if (rc) {
	root_device_unregister(kvm_root);
	return rc;
	}

	kvm_devices = (void *) real_memory_size;

	INIT_WORK(&hotplug_work, hotplug_devices);

	service_subclass_irq_register();
	register_external_interrupt(0x2603, kvm_extint_handler);

	scan_devices();
	return 0;
	}

	/* code for early console output with virtio_console */
	static __init int early_put_chars(u32 vtermno, const char *buf, int count)
	{
	char scratch[17];
	unsigned int len = count;

	if (len > sizeof(scratch) - 1)
	len = sizeof(scratch) - 1;
	scratch[len] = '\0';
	memcpy(scratch, buf, len);
	kvm_hypercall1(KVM_S390_VIRTIO_NOTIFY, __pa(scratch));
	return len;
	}

	static int __init s390_virtio_console_init(void)
	{
	if (!MACHINE_IS_KVM)
	return -ENODEV;
	return virtio_cons_early_init(early_put_chars);
	}
	console_initcall(s390_virtio_console_init);


	/*
	* We do this after core stuff, but before the drivers.
	*/
	postcore_initcall(kvm_devices_init);