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