blob: e2eec38c83c2ef21248353d132e3308810e1e17d [file] [log] [blame]
/*P:050 Lguest guests use a very simple method to describe devices. It's a
* series of device descriptors contained just above the top of normal
* memory.
* We use the standard "virtio" device infrastructure, which provides us with a
* console, a network and a block driver. Each one expects some configuration
* information and a "virtqueue" mechanism to send and receive data. :*/
#include <linux/init.h>
#include <linux/bootmem.h>
#include <linux/lguest_launcher.h>
#include <linux/virtio.h>
#include <linux/virtio_config.h>
#include <linux/interrupt.h>
#include <linux/virtio_ring.h>
#include <linux/err.h>
#include <asm/io.h>
#include <asm/paravirt.h>
#include <asm/lguest_hcall.h>
/* The pointer to our (page) of device descriptions. */
static void *lguest_devices;
/* Unique numbering for lguest devices. */
static unsigned int dev_index;
/* For Guests, device memory can be used as normal memory, so we cast away the
* __iomem to quieten sparse. */
static inline void *lguest_map(unsigned long phys_addr, unsigned long pages)
return (__force void *)ioremap(phys_addr, PAGE_SIZE*pages);
static inline void lguest_unmap(void *addr)
iounmap((__force void __iomem *)addr);
/*D:100 Each lguest device is just a virtio device plus a pointer to its entry
* in the lguest_devices page. */
struct lguest_device {
struct virtio_device vdev;
/* The entry in the lguest_devices page for this device. */
struct lguest_device_desc *desc;
/* Since the virtio infrastructure hands us a pointer to the virtio_device all
* the time, it helps to have a curt macro to get a pointer to the struct
* lguest_device it's enclosed in. */
#define to_lgdev(vdev) container_of(vdev, struct lguest_device, vdev)
* Device configurations
* The configuration information for a device consists of a series of fields.
* We don't really care what they are: the Launcher set them up, and the driver
* will look at them during setup.
* For us these fields come immediately after that device's descriptor in the
* lguest_devices page.
* Each field starts with a "type" byte, a "length" byte, then that number of
* bytes of configuration information. The device descriptor tells us the
* total configuration length so we know when we've reached the last field. */
/* type + length bytes */
#define FHDR_LEN 2
/* This finds the first field of a given type for a device's configuration. */
static void *lg_find(struct virtio_device *vdev, u8 type, unsigned int *len)
struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
int i;
for (i = 0; i < desc->config_len; i += FHDR_LEN + desc->config[i+1]) {
if (desc->config[i] == type) {
/* Mark it used, so Host can know we looked at it, and
* also so we won't find the same one twice. */
desc->config[i] |= 0x80;
/* Remember, the second byte is the length. */
*len = desc->config[i+1];
/* We return a pointer to the field header. */
return desc->config + i;
/* Not found: return NULL for failure. */
return NULL;
/* Once they've found a field, getting a copy of it is easy. */
static void lg_get(struct virtio_device *vdev, void *token,
void *buf, unsigned len)
/* Check they didn't ask for more than the length of the field! */
BUG_ON(len > ((u8 *)token)[1]);
memcpy(buf, token + FHDR_LEN, len);
/* Setting the contents is also trivial. */
static void lg_set(struct virtio_device *vdev, void *token,
const void *buf, unsigned len)
BUG_ON(len > ((u8 *)token)[1]);
memcpy(token + FHDR_LEN, buf, len);
/* The operations to get and set the status word just access the status field
* of the device descriptor. */
static u8 lg_get_status(struct virtio_device *vdev)
return to_lgdev(vdev)->desc->status;
static void lg_set_status(struct virtio_device *vdev, u8 status)
to_lgdev(vdev)->desc->status = status;
* Virtqueues
* The other piece of infrastructure virtio needs is a "virtqueue": a way of
* the Guest device registering buffers for the other side to read from or
* write into (ie. send and receive buffers). Each device can have multiple
* virtqueues: for example the console driver uses one queue for sending and
* another for receiving.
* Fortunately for us, a very fast shared-memory-plus-descriptors virtqueue
* already exists in virtio_ring.c. We just need to connect it up.
* We start with the information we need to keep about each virtqueue.
/*D:140 This is the information we remember about each virtqueue. */
struct lguest_vq_info
/* A copy of the information contained in the device config. */
struct lguest_vqconfig config;
/* The address where we mapped the virtio ring, so we can unmap it. */
void *pages;
/* When the virtio_ring code wants to prod the Host, it calls us here and we
* make a hypercall. We hand the page number of the virtqueue so the Host
* knows which virtqueue we're talking about. */
static void lg_notify(struct virtqueue *vq)
/* We store our virtqueue information in the "priv" pointer of the
* virtqueue structure. */
struct lguest_vq_info *lvq = vq->priv;
hcall(LHCALL_NOTIFY, lvq->config.pfn << PAGE_SHIFT, 0, 0);
/* This routine finds the first virtqueue described in the configuration of
* this device and sets it up.
* This is kind of an ugly duckling. It'd be nicer to have a standard
* representation of a virtqueue in the configuration space, but it seems that
* everyone wants to do it differently. The KVM coders want the Guest to
* allocate its own pages and tell the Host where they are, but for lguest it's
* simpler for the Host to simply tell us where the pages are.
* So we provide devices with a "find virtqueue and set it up" function. */
static struct virtqueue *lg_find_vq(struct virtio_device *vdev,
bool (*callback)(struct virtqueue *vq))
struct lguest_vq_info *lvq;
struct virtqueue *vq;
unsigned int len;
void *token;
int err;
/* Look for a field of the correct type to mark a virtqueue. Note that
* if this succeeds, then the type will be changed so it won't be found
* again, and future lg_find_vq() calls will find the next
* virtqueue (if any). */
token = vdev->config->find(vdev, VIRTIO_CONFIG_F_VIRTQUEUE, &len);
if (!token)
return ERR_PTR(-ENOENT);
lvq = kmalloc(sizeof(*lvq), GFP_KERNEL);
if (!lvq)
return ERR_PTR(-ENOMEM);
/* Note: we could use a configuration space inside here, just like we
* do for the device. This would allow expansion in future, because
* our configuration system is designed to be expansible. But this is
* way easier. */
if (len != sizeof(lvq->config)) {
dev_err(&vdev->dev, "Unexpected virtio config len %u\n", len);
err = -EIO;
goto free_lvq;
/* Make a copy of the "struct lguest_vqconfig" field. We need a copy
* because the config space might not be aligned correctly. */
vdev->config->get(vdev, token, &lvq->config, sizeof(lvq->config));
/* Figure out how many pages the ring will take, and map that memory */
lvq->pages = lguest_map((unsigned long)lvq->config.pfn << PAGE_SHIFT,
if (!lvq->pages) {
err = -ENOMEM;
goto free_lvq;
/* OK, tell virtio_ring.c to set up a virtqueue now we know its size
* and we've got a pointer to its pages. */
vq = vring_new_virtqueue(lvq->config.num, vdev, lvq->pages,
lg_notify, callback);
if (!vq) {
err = -ENOMEM;
goto unmap;
/* Tell the interrupt for this virtqueue to go to the virtio_ring
* interrupt handler. */
/* FIXME: We used to have a flag for the Host to tell us we could use
* the interrupt as a source of randomness: it'd be nice to have that
* back.. */
err = request_irq(lvq->config.irq, vring_interrupt, IRQF_SHARED,
vdev->dev.bus_id, vq);
if (err)
goto destroy_vring;
/* Last of all we hook up our 'struct lguest_vq_info" to the
* virtqueue's priv pointer. */
vq->priv = lvq;
return vq;
return ERR_PTR(err);
/* Cleaning up a virtqueue is easy */
static void lg_del_vq(struct virtqueue *vq)
struct lguest_vq_info *lvq = vq->priv;
/* Release the interrupt */
free_irq(lvq->config.irq, vq);
/* Tell virtio_ring.c to free the virtqueue. */
/* Unmap the pages containing the ring. */
/* Free our own queue information. */
/* The ops structure which hooks everything together. */
static struct virtio_config_ops lguest_config_ops = {
.find = lg_find,
.get = lg_get,
.set = lg_set,
.get_status = lg_get_status,
.set_status = lg_set_status,
.find_vq = lg_find_vq,
.del_vq = lg_del_vq,
/* The root device for the lguest virtio devices. This makes them appear as
* /sys/devices/lguest/0,1,2 not /sys/devices/0,1,2. */
static struct device lguest_root = {
.parent = NULL,
.bus_id = "lguest",
/*D:120 This is the core of the lguest bus: actually adding a new device.
* It's a separate function because it's neater that way, and because an
* earlier version of the code supported hotplug and unplug. They were removed
* early on because they were never used.
* As Andrew Tridgell says, "Untested code is buggy code".
* It's worth reading this carefully: we start with a pointer to the new device
* descriptor in the "lguest_devices" page. */
static void add_lguest_device(struct lguest_device_desc *d)
struct lguest_device *ldev;
/* Start with zeroed memory; Linux's device layer seems to count on
* it. */
ldev = kzalloc(sizeof(*ldev), GFP_KERNEL);
if (!ldev) {
printk(KERN_EMERG "Cannot allocate lguest dev %u\n",
/* This devices' parent is the lguest/ dir. */
ldev-> = &lguest_root;
/* We have a unique device index thanks to the dev_index counter. */
ldev->vdev.index = dev_index++;
/* The device type comes straight from the descriptor. There's also a
* device vendor field in the virtio_device struct, which we leave as
* 0. */
ldev-> = d->type;
/* We have a simple set of routines for querying the device's
* configuration information and setting its status. */
ldev->vdev.config = &lguest_config_ops;
/* And we remember the device's descriptor for lguest_config_ops. */
ldev->desc = d;
/* register_virtio_device() sets up the generic fields for the struct
* virtio_device and calls device_register(). This makes the bus
* infrastructure look for a matching driver. */
if (register_virtio_device(&ldev->vdev) != 0) {
printk(KERN_ERR "Failed to register lguest device %u\n",
/*D:110 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 lguest_device_desc *d;
/* We start at the page beginning, and skip over each entry. */
for (i = 0; i < PAGE_SIZE; i += sizeof(*d) + d->config_len) {
d = lguest_devices + i;
/* Once we hit a zero, stop. */
if (d->type == 0)
/*D:105 Fairly early in boot, lguest_devices_init() is called to set up the
* lguest device infrastructure. We check that we are a Guest by checking
* there are other ways of checking, but this seems most
* obvious to me.
* So we can access the "struct lguest_device_desc"s easily, we map that memory
* and store the pointer in the global "lguest_devices". Then we register a
* root device from which all our devices will hang (this seems to be the
* correct sysfs incantation).
* Finally we call scan_devices() which adds all the devices found in the
* lguest_devices page. */
static int __init lguest_devices_init(void)
if (strcmp(, "lguest") != 0)
return 0;
if (device_register(&lguest_root) != 0)
panic("Could not register lguest root");
/* Devices are in a single page above top of "normal" mem */
lguest_devices = lguest_map(max_pfn<<PAGE_SHIFT, 1);
return 0;
/* We do this after core stuff, but before the drivers. */
/*D:150 At this point in the journey we used to now wade through the lguest
* devices themselves: net, block and console. Since they're all now virtio
* devices rather than lguest-specific, I've decided to ignore them. Mostly,
* they're kind of boring. But this does mean you'll never experience the
* thrill of reading the forbidden love scene buried deep in the block driver.
* "make Launcher" beckons, where we answer questions like "Where do Guests
* come from?", and "What do you do when someone asks for optimization?". */