drivers/lguest/lguest_device.c

   1 /*P:050 Lguest guests use a very simple method to describe devices.  It's a
   2  * series of device descriptors contained just above the top of normal
   3  * memory.
   4  *
   5  * We use the standard "virtio" device infrastructure, which provides us with a
   6  * console, a network and a block driver.  Each one expects some configuration
   7  * information and a "virtqueue" mechanism to send and receive data. :*/
   8 #include <linux/init.h>
   9 #include <linux/bootmem.h>
  10 #include <linux/lguest_launcher.h>
  11 #include <linux/virtio.h>
  12 #include <linux/virtio_config.h>
  13 #include <linux/interrupt.h>
  14 #include <linux/virtio_ring.h>
  15 #include <linux/err.h>
  16 #include <asm/io.h>
  17 #include <asm/paravirt.h>
  18 #include <asm/lguest_hcall.h>
  19
  20 /* The pointer to our (page) of device descriptions. */
  21 static void *lguest_devices;
  22
  23 /* Unique numbering for lguest devices. */
  24 static unsigned int dev_index;
  25
  26 /* For Guests, device memory can be used as normal memory, so we cast away the
  27  * __iomem to quieten sparse. */
  28 static inline void *lguest_map(unsigned long phys_addr, unsigned long pages)
  29 {
  30         return (__force void *)ioremap(phys_addr, PAGE_SIZE*pages);
  31 }
  32
  33 static inline void lguest_unmap(void *addr)
  34 {
  35         iounmap((__force void __iomem *)addr);
  36 }
  37
  38 /*D:100 Each lguest device is just a virtio device plus a pointer to its entry
  39  * in the lguest_devices page. */
  40 struct lguest_device {
  41         struct virtio_device vdev;
  42
  43         /* The entry in the lguest_devices page for this device. */
  44         struct lguest_device_desc *desc;
  45 };
  46
  47 /* Since the virtio infrastructure hands us a pointer to the virtio_device all
  48  * the time, it helps to have a curt macro to get a pointer to the struct
  49  * lguest_device it's enclosed in.  */
  50 #define to_lgdev(vdev) container_of(vdev, struct lguest_device, vdev)
  51
  52 /*D:130
  53  * Device configurations
  54  *
  55  * The configuration information for a device consists of a series of fields.
  56  * We don't really care what they are: the Launcher set them up, and the driver
  57  * will look at them during setup.
  58  *
  59  * For us these fields come immediately after that device's descriptor in the
  60  * lguest_devices page.
  61  *
  62  * Each field starts with a "type" byte, a "length" byte, then that number of
  63  * bytes of configuration information.  The device descriptor tells us the
  64  * total configuration length so we know when we've reached the last field. */
  65
  66 /* type + length bytes */
  67 #define FHDR_LEN 2
  68
  69 /* This finds the first field of a given type for a device's configuration. */
  70 static void *lg_find(struct virtio_device *vdev, u8 type, unsigned int *len)
  71 {
  72         struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
  73         int i;
  74
  75         for (i = 0; i < desc->config_len; i += FHDR_LEN + desc->config[i+1]) {
  76                 if (desc->config[i] == type) {
  77                         /* Mark it used, so Host can know we looked at it, and
  78                          * also so we won't find the same one twice. */
  79                         desc->config[i] |= 0x80;
  80                         /* Remember, the second byte is the length. */
  81                         *len = desc->config[i+1];
  82                         /* We return a pointer to the field header. */
  83                         return desc->config + i;
  84                 }
  85         }
  86
  87         /* Not found: return NULL for failure. */
  88         return NULL;
  89 }
  90
  91 /* Once they've found a field, getting a copy of it is easy. */
  92 static void lg_get(struct virtio_device *vdev, void *token,
  93                    void *buf, unsigned len)
  94 {
  95         /* Check they didn't ask for more than the length of the field! */
  96         BUG_ON(len > ((u8 *)token)[1]);
  97         memcpy(buf, token + FHDR_LEN, len);
  98 }
  99
 100 /* Setting the contents is also trivial. */
 101 static void lg_set(struct virtio_device *vdev, void *token,
 102                    const void *buf, unsigned len)
 103 {
 104         BUG_ON(len > ((u8 *)token)[1]);
 105         memcpy(token + FHDR_LEN, buf, len);
 106 }
 107
 108 /* The operations to get and set the status word just access the status field
 109  * of the device descriptor. */
 110 static u8 lg_get_status(struct virtio_device *vdev)
 111 {
 112         return to_lgdev(vdev)->desc->status;
 113 }
 114
 115 static void lg_set_status(struct virtio_device *vdev, u8 status)
 116 {
 117         to_lgdev(vdev)->desc->status = status;
 118 }
 119
 120 /*
 121  * Virtqueues
 122  *
 123  * The other piece of infrastructure virtio needs is a "virtqueue": a way of
 124  * the Guest device registering buffers for the other side to read from or
 125  * write into (ie. send and receive buffers).  Each device can have multiple
 126  * virtqueues: for example the console driver uses one queue for sending and
 127  * another for receiving.
 128  *
 129  * Fortunately for us, a very fast shared-memory-plus-descriptors virtqueue
 130  * already exists in virtio_ring.c.  We just need to connect it up.
 131  *
 132  * We start with the information we need to keep about each virtqueue.
 133  */
 134
 135 /*D:140 This is the information we remember about each virtqueue. */
 136 struct lguest_vq_info
 137 {
 138         /* A copy of the information contained in the device config. */
 139         struct lguest_vqconfig config;
 140
 141         /* The address where we mapped the virtio ring, so we can unmap it. */
 142         void *pages;
 143 };
 144
 145 /* When the virtio_ring code wants to prod the Host, it calls us here and we
 146  * make a hypercall.  We hand the page number of the virtqueue so the Host
 147  * knows which virtqueue we're talking about. */
 148 static void lg_notify(struct virtqueue *vq)
 149 {
 150         /* We store our virtqueue information in the "priv" pointer of the
 151          * virtqueue structure. */
 152         struct lguest_vq_info *lvq = vq->priv;
 153
 154         hcall(LHCALL_NOTIFY, lvq->config.pfn << PAGE_SHIFT, 0, 0);
 155 }
 156
 157 /* This routine finds the first virtqueue described in the configuration of
 158  * this device and sets it up.
 159  *
 160  * This is kind of an ugly duckling.  It'd be nicer to have a standard
 161  * representation of a virtqueue in the configuration space, but it seems that
 162  * everyone wants to do it differently.  The KVM coders want the Guest to
 163  * allocate its own pages and tell the Host where they are, but for lguest it's
 164  * simpler for the Host to simply tell us where the pages are.
 165  *
 166  * So we provide devices with a "find virtqueue and set it up" function. */
 167 static struct virtqueue *lg_find_vq(struct virtio_device *vdev,
 168                                     bool (*callback)(struct virtqueue *vq))
 169 {
 170         struct lguest_vq_info *lvq;
 171         struct virtqueue *vq;
 172         unsigned int len;
 173         void *token;
 174         int err;
 175
 176         /* Look for a field of the correct type to mark a virtqueue.  Note that
 177          * if this succeeds, then the type will be changed so it won't be found
 178          * again, and future lg_find_vq() calls will find the next
 179          * virtqueue (if any). */
 180         token = vdev->config->find(vdev, VIRTIO_CONFIG_F_VIRTQUEUE, &len);
 181         if (!token)
 182                 return ERR_PTR(-ENOENT);
 183
 184         lvq = kmalloc(sizeof(*lvq), GFP_KERNEL);
 185         if (!lvq)
 186                 return ERR_PTR(-ENOMEM);
 187
 188         /* Note: we could use a configuration space inside here, just like we
 189          * do for the device.  This would allow expansion in future, because
 190          * our configuration system is designed to be expansible.  But this is
 191          * way easier. */
 192         if (len != sizeof(lvq->config)) {
 193                 dev_err(&vdev->dev, "Unexpected virtio config len %u\n", len);
 194                 err = -EIO;
 195                 goto free_lvq;
 196         }
 197         /* Make a copy of the "struct lguest_vqconfig" field.  We need a copy
 198          * because the config space might not be aligned correctly. */
 199         vdev->config->get(vdev, token, &lvq->config, sizeof(lvq->config));
 200
 201         /* Figure out how many pages the ring will take, and map that memory */
 202         lvq->pages = lguest_map((unsigned long)lvq->config.pfn << PAGE_SHIFT,
 203                                 DIV_ROUND_UP(vring_size(lvq->config.num,
 204                                                         PAGE_SIZE),
 205                                              PAGE_SIZE));
 206         if (!lvq->pages) {
 207                 err = -ENOMEM;
 208                 goto free_lvq;
 209         }
 210
 211         /* OK, tell virtio_ring.c to set up a virtqueue now we know its size
 212          * and we've got a pointer to its pages. */
 213         vq = vring_new_virtqueue(lvq->config.num, vdev, lvq->pages,
 214                                  lg_notify, callback);
 215         if (!vq) {
 216                 err = -ENOMEM;
 217                 goto unmap;
 218         }
 219
 220         /* Tell the interrupt for this virtqueue to go to the virtio_ring
 221          * interrupt handler. */
 222         /* FIXME: We used to have a flag for the Host to tell us we could use
 223          * the interrupt as a source of randomness: it'd be nice to have that
 224          * back.. */
 225         err = request_irq(lvq->config.irq, vring_interrupt, IRQF_SHARED,
 226                           vdev->dev.bus_id, vq);
 227         if (err)
 228                 goto destroy_vring;
 229
 230         /* Last of all we hook up our 'struct lguest_vq_info" to the
 231          * virtqueue's priv pointer. */
 232         vq->priv = lvq;
 233         return vq;
 234
 235 destroy_vring:
 236         vring_del_virtqueue(vq);
 237 unmap:
 238         lguest_unmap(lvq->pages);
 239 free_lvq:
 240         kfree(lvq);
 241         return ERR_PTR(err);
 242 }
 243 /*:*/
 244
 245 /* Cleaning up a virtqueue is easy */
 246 static void lg_del_vq(struct virtqueue *vq)
 247 {
 248         struct lguest_vq_info *lvq = vq->priv;
 249
 250         /* Tell virtio_ring.c to free the virtqueue. */
 251         vring_del_virtqueue(vq);
 252         /* Unmap the pages containing the ring. */
 253         lguest_unmap(lvq->pages);
 254         /* Free our own queue information. */
 255         kfree(lvq);
 256 }
 257
 258 /* The ops structure which hooks everything together. */
 259 static struct virtio_config_ops lguest_config_ops = {
 260         .find = lg_find,
 261         .get = lg_get,
 262         .set = lg_set,
 263         .get_status = lg_get_status,
 264         .set_status = lg_set_status,
 265         .find_vq = lg_find_vq,
 266         .del_vq = lg_del_vq,
 267 };
 268
 269 /* The root device for the lguest virtio devices.  This makes them appear as
 270  * /sys/devices/lguest/0,1,2 not /sys/devices/0,1,2. */
 271 static struct device lguest_root = {
 272         .parent = NULL,
 273         .bus_id = "lguest",
 274 };
 275
 276 /*D:120 This is the core of the lguest bus: actually adding a new device.
 277  * It's a separate function because it's neater that way, and because an
 278  * earlier version of the code supported hotplug and unplug.  They were removed
 279  * early on because they were never used.
 280  *
 281  * As Andrew Tridgell says, "Untested code is buggy code".
 282  *
 283  * It's worth reading this carefully: we start with a pointer to the new device
 284  * descriptor in the "lguest_devices" page. */
 285 static void add_lguest_device(struct lguest_device_desc *d)
 286 {
 287         struct lguest_device *ldev;
 288
 289         /* Start with zeroed memory; Linux's device layer seems to count on
 290          * it. */
 291         ldev = kzalloc(sizeof(*ldev), GFP_KERNEL);
 292         if (!ldev) {
 293                 printk(KERN_EMERG "Cannot allocate lguest dev %u\n",
 294                        dev_index++);
 295                 return;
 296         }
 297
 298         /* This devices' parent is the lguest/ dir. */
 299         ldev->vdev.dev.parent = &lguest_root;
 300         /* We have a unique device index thanks to the dev_index counter. */
 301         ldev->vdev.index = dev_index++;
 302         /* The device type comes straight from the descriptor.  There's also a
 303          * device vendor field in the virtio_device struct, which we leave as
 304          * 0. */
 305         ldev->vdev.id.device = d->type;
 306         /* We have a simple set of routines for querying the device's
 307          * configuration information and setting its status. */
 308         ldev->vdev.config = &lguest_config_ops;
 309         /* And we remember the device's descriptor for lguest_config_ops. */
 310         ldev->desc = d;
 311
 312         /* register_virtio_device() sets up the generic fields for the struct
 313          * virtio_device and calls device_register().  This makes the bus
 314          * infrastructure look for a matching driver. */
 315         if (register_virtio_device(&ldev->vdev) != 0) {
 316                 printk(KERN_ERR "Failed to register lguest device %u\n",
 317                        ldev->vdev.index);
 318                 kfree(ldev);
 319         }
 320 }
 321
 322 /*D:110 scan_devices() simply iterates through the device page.  The type 0 is
 323  * reserved to mean "end of devices". */
 324 static void scan_devices(void)
 325 {
 326         unsigned int i;
 327         struct lguest_device_desc *d;
 328
 329         /* We start at the page beginning, and skip over each entry. */
 330         for (i = 0; i < PAGE_SIZE; i += sizeof(*d) + d->config_len) {
 331                 d = lguest_devices + i;
 332
 333                 /* Once we hit a zero, stop. */
 334                 if (d->type == 0)
 335                         break;
 336
 337                 add_lguest_device(d);
 338         }
 339 }
 340
 341 /*D:105 Fairly early in boot, lguest_devices_init() is called to set up the
 342  * lguest device infrastructure.  We check that we are a Guest by checking
 343  * pv_info.name: there are other ways of checking, but this seems most
 344  * obvious to me.
 345  *
 346  * So we can access the "struct lguest_device_desc"s easily, we map that memory
 347  * and store the pointer in the global "lguest_devices".  Then we register a
 348  * root device from which all our devices will hang (this seems to be the
 349  * correct sysfs incantation).
 350  *
 351  * Finally we call scan_devices() which adds all the devices found in the
 352  * lguest_devices page. */
 353 static int __init lguest_devices_init(void)
 354 {
 355         if (strcmp(pv_info.name, "lguest") != 0)
 356                 return 0;
 357
 358         if (device_register(&lguest_root) != 0)
 359                 panic("Could not register lguest root");
 360
 361         /* Devices are in a single page above top of "normal" mem */
 362         lguest_devices = lguest_map(max_pfn<<PAGE_SHIFT, 1);
 363
 364         scan_devices();
 365         return 0;
 366 }
 367 /* We do this after core stuff, but before the drivers. */
 368 postcore_initcall(lguest_devices_init);
 369
 370 /*D:150 At this point in the journey we used to now wade through the lguest
 371  * devices themselves: net, block and console.  Since they're all now virtio
 372  * devices rather than lguest-specific, I've decided to ignore them.  Mostly,
 373  * they're kind of boring.  But this does mean you'll never experience the
 374  * thrill of reading the forbidden love scene buried deep in the block driver.
 375  *
 376  * "make Launcher" beckons, where we answer questions like "Where do Guests
 377  * come from?", and "What do you do when someone asks for optimization?". */