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 Guest
   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" or two 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 /* For Guests, device memory can be used as normal memory, so we cast away the
  24  * __iomem to quieten sparse. */
  25 static inline void *lguest_map(unsigned long phys_addr, unsigned long pages)
  26 {
  27         return (__force void *)ioremap_cache(phys_addr, PAGE_SIZE*pages);
  28 }
  29
  30 static inline void lguest_unmap(void *addr)
  31 {
  32         iounmap((__force void __iomem *)addr);
  33 }
  34
  35 /*D:100 Each lguest device is just a virtio device plus a pointer to its entry
  36  * in the lguest_devices page. */
  37 struct lguest_device {
  38         struct virtio_device vdev;
  39
  40         /* The entry in the lguest_devices page for this device. */
  41         struct lguest_device_desc *desc;
  42 };
  43
  44 /* Since the virtio infrastructure hands us a pointer to the virtio_device all
  45  * the time, it helps to have a curt macro to get a pointer to the struct
  46  * lguest_device it's enclosed in.  */
  47 #define to_lgdev(vd) container_of(vd, struct lguest_device, vdev)
  48
  49 /*D:130
  50  * Device configurations
  51  *
  52  * The configuration information for a device consists of one or more
  53  * virtqueues, a feature bitmap, and some configuration bytes.  The
  54  * configuration bytes don't really matter to us: the Launcher sets them up, and
  55  * the driver will look at them during setup.
  56  *
  57  * A convenient routine to return the device's virtqueue config array:
  58  * immediately after the descriptor. */
  59 static struct lguest_vqconfig *lg_vq(const struct lguest_device_desc *desc)
  60 {
  61         return (void *)(desc + 1);
  62 }
  63
  64 /* The features come immediately after the virtqueues. */
  65 static u8 *lg_features(const struct lguest_device_desc *desc)
  66 {
  67         return (void *)(lg_vq(desc) + desc->num_vq);
  68 }
  69
  70 /* The config space comes after the two feature bitmasks. */
  71 static u8 *lg_config(const struct lguest_device_desc *desc)
  72 {
  73         return lg_features(desc) + desc->feature_len * 2;
  74 }
  75
  76 /* The total size of the config page used by this device (incl. desc) */
  77 static unsigned desc_size(const struct lguest_device_desc *desc)
  78 {
  79         return sizeof(*desc)
  80                 + desc->num_vq * sizeof(struct lguest_vqconfig)
  81                 + desc->feature_len * 2
  82                 + desc->config_len;
  83 }
  84
  85 /* This gets the device's feature bits. */
  86 static u32 lg_get_features(struct virtio_device *vdev)
  87 {
  88         unsigned int i;
  89         u32 features = 0;
  90         struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
  91         u8 *in_features = lg_features(desc);
  92
  93         /* We do this the slow but generic way. */
  94         for (i = 0; i < min(desc->feature_len * 8, 32); i++)
  95                 if (in_features[i / 8] & (1 << (i % 8)))
  96                         features |= (1 << i);
  97
  98         return features;
  99 }
 100
 101 static void lg_set_features(struct virtio_device *vdev, u32 features)
 102 {
 103         unsigned int i;
 104         struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
 105         /* Second half of bitmap is features we accept. */
 106         u8 *out_features = lg_features(desc) + desc->feature_len;
 107
 108         memset(out_features, 0, desc->feature_len);
 109         for (i = 0; i < min(desc->feature_len * 8, 32); i++) {
 110                 if (features & (1 << i))
 111                         out_features[i / 8] |= (1 << (i % 8));
 112         }
 113 }
 114
 115 /* Once they've found a field, getting a copy of it is easy. */
 116 static void lg_get(struct virtio_device *vdev, unsigned int offset,
 117                    void *buf, unsigned len)
 118 {
 119         struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
 120
 121         /* Check they didn't ask for more than the length of the config! */
 122         BUG_ON(offset + len > desc->config_len);
 123         memcpy(buf, lg_config(desc) + offset, len);
 124 }
 125
 126 /* Setting the contents is also trivial. */
 127 static void lg_set(struct virtio_device *vdev, unsigned int offset,
 128                    const void *buf, unsigned len)
 129 {
 130         struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
 131
 132         /* Check they didn't ask for more than the length of the config! */
 133         BUG_ON(offset + len > desc->config_len);
 134         memcpy(lg_config(desc) + offset, buf, len);
 135 }
 136
 137 /* The operations to get and set the status word just access the status field
 138  * of the device descriptor. */
 139 static u8 lg_get_status(struct virtio_device *vdev)
 140 {
 141         return to_lgdev(vdev)->desc->status;
 142 }
 143
 144 /* To notify on status updates, we (ab)use the NOTIFY hypercall, with the
 145  * descriptor address of the device.  A zero status means "reset". */
 146 static void set_status(struct virtio_device *vdev, u8 status)
 147 {
 148         unsigned long offset = (void *)to_lgdev(vdev)->desc - lguest_devices;
 149
 150         /* We set the status. */
 151         to_lgdev(vdev)->desc->status = status;
 152         hcall(LHCALL_NOTIFY, (max_pfn<<PAGE_SHIFT) + offset, 0, 0);
 153 }
 154
 155 static void lg_set_status(struct virtio_device *vdev, u8 status)
 156 {
 157         BUG_ON(!status);
 158         set_status(vdev, status);
 159 }
 160
 161 static void lg_reset(struct virtio_device *vdev)
 162 {
 163         set_status(vdev, 0);
 164 }
 165
 166 /*
 167  * Virtqueues
 168  *
 169  * The other piece of infrastructure virtio needs is a "virtqueue": a way of
 170  * the Guest device registering buffers for the other side to read from or
 171  * write into (ie. send and receive buffers).  Each device can have multiple
 172  * virtqueues: for example the console driver uses one queue for sending and
 173  * another for receiving.
 174  *
 175  * Fortunately for us, a very fast shared-memory-plus-descriptors virtqueue
 176  * already exists in virtio_ring.c.  We just need to connect it up.
 177  *
 178  * We start with the information we need to keep about each virtqueue.
 179  */
 180
 181 /*D:140 This is the information we remember about each virtqueue. */
 182 struct lguest_vq_info
 183 {
 184         /* A copy of the information contained in the device config. */
 185         struct lguest_vqconfig config;
 186
 187         /* The address where we mapped the virtio ring, so we can unmap it. */
 188         void *pages;
 189 };
 190
 191 /* When the virtio_ring code wants to prod the Host, it calls us here and we
 192  * make a hypercall.  We hand the physical address of the virtqueue so the Host
 193  * knows which virtqueue we're talking about. */
 194 static void lg_notify(struct virtqueue *vq)
 195 {
 196         /* We store our virtqueue information in the "priv" pointer of the
 197          * virtqueue structure. */
 198         struct lguest_vq_info *lvq = vq->priv;
 199
 200         hcall(LHCALL_NOTIFY, lvq->config.pfn << PAGE_SHIFT, 0, 0);
 201 }
 202
 203 /* This routine finds the first virtqueue described in the configuration of
 204  * this device and sets it up.
 205  *
 206  * This is kind of an ugly duckling.  It'd be nicer to have a standard
 207  * representation of a virtqueue in the configuration space, but it seems that
 208  * everyone wants to do it differently.  The KVM coders want the Guest to
 209  * allocate its own pages and tell the Host where they are, but for lguest it's
 210  * simpler for the Host to simply tell us where the pages are.
 211  *
 212  * So we provide drivers with a "find the Nth virtqueue and set it up"
 213  * function. */
 214 static struct virtqueue *lg_find_vq(struct virtio_device *vdev,
 215                                     unsigned index,
 216                                     void (*callback)(struct virtqueue *vq))
 217 {
 218         struct lguest_device *ldev = to_lgdev(vdev);
 219         struct lguest_vq_info *lvq;
 220         struct virtqueue *vq;
 221         int err;
 222
 223         /* We must have this many virtqueues. */
 224         if (index >= ldev->desc->num_vq)
 225                 return ERR_PTR(-ENOENT);
 226
 227         lvq = kmalloc(sizeof(*lvq), GFP_KERNEL);
 228         if (!lvq)
 229                 return ERR_PTR(-ENOMEM);
 230
 231         /* Make a copy of the "struct lguest_vqconfig" entry, which sits after
 232          * the descriptor.  We need a copy because the config space might not
 233          * be aligned correctly. */
 234         memcpy(&lvq->config, lg_vq(ldev->desc)+index, sizeof(lvq->config));
 235
 236         printk("Mapping virtqueue %i addr %lx\n", index,
 237                (unsigned long)lvq->config.pfn << PAGE_SHIFT);
 238         /* Figure out how many pages the ring will take, and map that memory */
 239         lvq->pages = lguest_map((unsigned long)lvq->config.pfn << PAGE_SHIFT,
 240                                 DIV_ROUND_UP(vring_size(lvq->config.num,
 241                                                         PAGE_SIZE),
 242                                              PAGE_SIZE));
 243         if (!lvq->pages) {
 244                 err = -ENOMEM;
 245                 goto free_lvq;
 246         }
 247
 248         /* OK, tell virtio_ring.c to set up a virtqueue now we know its size
 249          * and we've got a pointer to its pages. */
 250         vq = vring_new_virtqueue(lvq->config.num, vdev, lvq->pages,
 251                                  lg_notify, callback);
 252         if (!vq) {
 253                 err = -ENOMEM;
 254                 goto unmap;
 255         }
 256
 257         /* Tell the interrupt for this virtqueue to go to the virtio_ring
 258          * interrupt handler. */
 259         /* FIXME: We used to have a flag for the Host to tell us we could use
 260          * the interrupt as a source of randomness: it'd be nice to have that
 261          * back.. */
 262         err = request_irq(lvq->config.irq, vring_interrupt, IRQF_SHARED,
 263                           vdev->dev.bus_id, vq);
 264         if (err)
 265                 goto destroy_vring;
 266
 267         /* Last of all we hook up our 'struct lguest_vq_info" to the
 268          * virtqueue's priv pointer. */
 269         vq->priv = lvq;
 270         return vq;
 271
 272 destroy_vring:
 273         vring_del_virtqueue(vq);
 274 unmap:
 275         lguest_unmap(lvq->pages);
 276 free_lvq:
 277         kfree(lvq);
 278         return ERR_PTR(err);
 279 }
 280 /*:*/
 281
 282 /* Cleaning up a virtqueue is easy */
 283 static void lg_del_vq(struct virtqueue *vq)
 284 {
 285         struct lguest_vq_info *lvq = vq->priv;
 286
 287         /* Release the interrupt */
 288         free_irq(lvq->config.irq, vq);
 289         /* Tell virtio_ring.c to free the virtqueue. */
 290         vring_del_virtqueue(vq);
 291         /* Unmap the pages containing the ring. */
 292         lguest_unmap(lvq->pages);
 293         /* Free our own queue information. */
 294         kfree(lvq);
 295 }
 296
 297 /* The ops structure which hooks everything together. */
 298 static struct virtio_config_ops lguest_config_ops = {
 299         .get_features = lg_get_features,
 300         .set_features = lg_set_features,
 301         .get = lg_get,
 302         .set = lg_set,
 303         .get_status = lg_get_status,
 304         .set_status = lg_set_status,
 305         .reset = lg_reset,
 306         .find_vq = lg_find_vq,
 307         .del_vq = lg_del_vq,
 308 };
 309
 310 /* The root device for the lguest virtio devices.  This makes them appear as
 311  * /sys/devices/lguest/0,1,2 not /sys/devices/0,1,2. */
 312 static struct device lguest_root = {
 313         .parent = NULL,
 314         .bus_id = "lguest",
 315 };
 316
 317 /*D:120 This is the core of the lguest bus: actually adding a new device.
 318  * It's a separate function because it's neater that way, and because an
 319  * earlier version of the code supported hotplug and unplug.  They were removed
 320  * early on because they were never used.
 321  *
 322  * As Andrew Tridgell says, "Untested code is buggy code".
 323  *
 324  * It's worth reading this carefully: we start with a pointer to the new device
 325  * descriptor in the "lguest_devices" page, and the offset into the device
 326  * descriptor page so we can uniquely identify it if things go badly wrong. */
 327 static void add_lguest_device(struct lguest_device_desc *d,
 328                               unsigned int offset)
 329 {
 330         struct lguest_device *ldev;
 331
 332         /* Start with zeroed memory; Linux's device layer seems to count on
 333          * it. */
 334         ldev = kzalloc(sizeof(*ldev), GFP_KERNEL);
 335         if (!ldev) {
 336                 printk(KERN_EMERG "Cannot allocate lguest dev %u type %u\n",
 337                        offset, d->type);
 338                 return;
 339         }
 340
 341         /* This devices' parent is the lguest/ dir. */
 342         ldev->vdev.dev.parent = &lguest_root;
 343         /* We have a unique device index thanks to the dev_index counter. */
 344         ldev->vdev.id.device = d->type;
 345         /* We have a simple set of routines for querying the device's
 346          * configuration information and setting its status. */
 347         ldev->vdev.config = &lguest_config_ops;
 348         /* And we remember the device's descriptor for lguest_config_ops. */
 349         ldev->desc = d;
 350
 351         /* register_virtio_device() sets up the generic fields for the struct
 352          * virtio_device and calls device_register().  This makes the bus
 353          * infrastructure look for a matching driver. */
 354         if (register_virtio_device(&ldev->vdev) != 0) {
 355                 printk(KERN_ERR "Failed to register lguest dev %u type %u\n",
 356                        offset, d->type);
 357                 kfree(ldev);
 358         }
 359 }
 360
 361 /*D:110 scan_devices() simply iterates through the device page.  The type 0 is
 362  * reserved to mean "end of devices". */
 363 static void scan_devices(void)
 364 {
 365         unsigned int i;
 366         struct lguest_device_desc *d;
 367
 368         /* We start at the page beginning, and skip over each entry. */
 369         for (i = 0; i < PAGE_SIZE; i += desc_size(d)) {
 370                 d = lguest_devices + i;
 371
 372                 /* Once we hit a zero, stop. */
 373                 if (d->type == 0)
 374                         break;
 375
 376                 printk("Device at %i has size %u\n", i, desc_size(d));
 377                 add_lguest_device(d, i);
 378         }
 379 }
 380
 381 /*D:105 Fairly early in boot, lguest_devices_init() is called to set up the
 382  * lguest device infrastructure.  We check that we are a Guest by checking
 383  * pv_info.name: there are other ways of checking, but this seems most
 384  * obvious to me.
 385  *
 386  * So we can access the "struct lguest_device_desc"s easily, we map that memory
 387  * and store the pointer in the global "lguest_devices".  Then we register a
 388  * root device from which all our devices will hang (this seems to be the
 389  * correct sysfs incantation).
 390  *
 391  * Finally we call scan_devices() which adds all the devices found in the
 392  * lguest_devices page. */
 393 static int __init lguest_devices_init(void)
 394 {
 395         if (strcmp(pv_info.name, "lguest") != 0)
 396                 return 0;
 397
 398         if (device_register(&lguest_root) != 0)
 399                 panic("Could not register lguest root");
 400
 401         /* Devices are in a single page above top of "normal" mem */
 402         lguest_devices = lguest_map(max_pfn<<PAGE_SHIFT, 1);
 403
 404         scan_devices();
 405         return 0;
 406 }
 407 /* We do this after core stuff, but before the drivers. */
 408 postcore_initcall(lguest_devices_init);
 409
 410 /*D:150 At this point in the journey we used to now wade through the lguest
 411  * devices themselves: net, block and console.  Since they're all now virtio
 412  * devices rather than lguest-specific, I've decided to ignore them.  Mostly,
 413  * they're kind of boring.  But this does mean you'll never experience the
 414  * thrill of reading the forbidden love scene buried deep in the block driver.
 415  *
 416  * "make Launcher" beckons, where we answer questions like "Where do Guests
 417  * come from?", and "What do you do when someone asks for optimization?". */