blob: 37344aaee22f3ab44910a18576489466c0b8c30d [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 Guest
* 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" or two 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;
/* 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_cache(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(vd) container_of(vd, struct lguest_device, vdev)
* Device configurations
* The configuration information for a device consists of one or more
* virtqueues, a feature bitmap, and some configuration bytes. The
* configuration bytes don't really matter to us: the Launcher sets them up, and
* the driver will look at them during setup.
* A convenient routine to return the device's virtqueue config array:
* immediately after the descriptor. */
static struct lguest_vqconfig *lg_vq(const struct lguest_device_desc *desc)
return (void *)(desc + 1);
/* The features come immediately after the virtqueues. */
static u8 *lg_features(const struct lguest_device_desc *desc)
return (void *)(lg_vq(desc) + desc->num_vq);
/* The config space comes after the two feature bitmasks. */
static u8 *lg_config(const struct lguest_device_desc *desc)
return lg_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 lguest_device_desc *desc)
return sizeof(*desc)
+ desc->num_vq * sizeof(struct lguest_vqconfig)
+ desc->feature_len * 2
+ desc->config_len;
/* This gets the device's feature bits. */
static u32 lg_get_features(struct virtio_device *vdev)
unsigned int i;
u32 features = 0;
struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
u8 *in_features = lg_features(desc);
/* We do this the slow but generic way. */
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 lg_finalize_features(struct virtio_device *vdev)
unsigned int i, bits;
struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
/* Second half of bitmap is features we accept. */
u8 *out_features = lg_features(desc) + desc->feature_len;
/* Give virtio_ring a chance to accept features. */
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));
/* Once they've found a field, getting a copy of it is easy. */
static void lg_get(struct virtio_device *vdev, unsigned int offset,
void *buf, unsigned len)
struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
/* Check they didn't ask for more than the length of the config! */
BUG_ON(offset + len > desc->config_len);
memcpy(buf, lg_config(desc) + offset, len);
/* Setting the contents is also trivial. */
static void lg_set(struct virtio_device *vdev, unsigned int offset,
const void *buf, unsigned len)
struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
/* Check they didn't ask for more than the length of the config! */
BUG_ON(offset + len > desc->config_len);
memcpy(lg_config(desc) + offset, 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;
/* To notify on status updates, we (ab)use the NOTIFY hypercall, with the
* descriptor address of the device. A zero status means "reset". */
static void set_status(struct virtio_device *vdev, u8 status)
unsigned long offset = (void *)to_lgdev(vdev)->desc - lguest_devices;
/* We set the status. */
to_lgdev(vdev)->desc->status = status;
hcall(LHCALL_NOTIFY, (max_pfn<<PAGE_SHIFT) + offset, 0, 0);
static void lg_set_status(struct virtio_device *vdev, u8 status)
set_status(vdev, status);
static void lg_reset(struct virtio_device *vdev)
set_status(vdev, 0);
* 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 physical address 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 drivers with a "find the Nth virtqueue and set it up"
* function. */
static struct virtqueue *lg_find_vq(struct virtio_device *vdev,
unsigned index,
void (*callback)(struct virtqueue *vq))
struct lguest_device *ldev = to_lgdev(vdev);
struct lguest_vq_info *lvq;
struct virtqueue *vq;
int err;
/* We must have this many virtqueues. */
if (index >= ldev->desc->num_vq)
return ERR_PTR(-ENOENT);
lvq = kmalloc(sizeof(*lvq), GFP_KERNEL);
if (!lvq)
return ERR_PTR(-ENOMEM);
/* Make a copy of the "struct lguest_vqconfig" entry, which sits after
* the descriptor. We need a copy because the config space might not
* be aligned correctly. */
memcpy(&lvq->config, lg_vq(ldev->desc)+index, sizeof(lvq->config));
printk("Mapping virtqueue %i addr %lx\n", index,
(unsigned long)lvq->config.pfn << PAGE_SHIFT);
/* 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 = {
.get_features = lg_get_features,
.finalize_features = lg_finalize_features,
.get = lg_get,
.set = lg_set,
.get_status = lg_get_status,
.set_status = lg_set_status,
.reset = lg_reset,
.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, and the offset into the device
* descriptor page so we can uniquely identify it if things go badly wrong. */
static void add_lguest_device(struct lguest_device_desc *d,
unsigned int offset)
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 type %u\n",
offset, d->type);
/* This devices' parent is the lguest/ dir. */
ldev-> = &lguest_root;
/* We have a unique device index thanks to the dev_index counter. */
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 dev %u type %u\n",
offset, d->type);
/*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 += desc_size(d)) {
d = lguest_devices + i;
/* Once we hit a zero, stop. */
if (d->type == 0)
printk("Device at %i has size %u\n", i, desc_size(d));
add_lguest_device(d, i);
/*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?". */