linux/drivers/lguest/lguest_device.c
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   1/*P:050
   2 * Lguest guests use a very simple method to describe devices.  It's a
   3 * series of device descriptors contained just above the top of normal Guest
   4 * memory.
   5 *
   6 * We use the standard "virtio" device infrastructure, which provides us with a
   7 * console, a network and a block driver.  Each one expects some configuration
   8 * information and a "virtqueue" or two to send and receive data.
   9:*/
  10#include <linux/init.h>
  11#include <linux/bootmem.h>
  12#include <linux/lguest_launcher.h>
  13#include <linux/virtio.h>
  14#include <linux/virtio_config.h>
  15#include <linux/interrupt.h>
  16#include <linux/virtio_ring.h>
  17#include <linux/err.h>
  18#include <linux/export.h>
  19#include <linux/slab.h>
  20#include <asm/io.h>
  21#include <asm/paravirt.h>
  22#include <asm/lguest_hcall.h>
  23
  24/* The pointer to our (page) of device descriptions. */
  25static void *lguest_devices;
  26
  27/*
  28 * For Guests, device memory can be used as normal memory, so we cast away the
  29 * __iomem to quieten sparse.
  30 */
  31static inline void *lguest_map(unsigned long phys_addr, unsigned long pages)
  32{
  33        return (__force void *)ioremap_cache(phys_addr, PAGE_SIZE*pages);
  34}
  35
  36static inline void lguest_unmap(void *addr)
  37{
  38        iounmap((__force void __iomem *)addr);
  39}
  40
  41/*D:100
  42 * Each lguest device is just a virtio device plus a pointer to its entry
  43 * in the lguest_devices page.
  44 */
  45struct lguest_device {
  46        struct virtio_device vdev;
  47
  48        /* The entry in the lguest_devices page for this device. */
  49        struct lguest_device_desc *desc;
  50};
  51
  52/*
  53 * Since the virtio infrastructure hands us a pointer to the virtio_device all
  54 * the time, it helps to have a curt macro to get a pointer to the struct
  55 * lguest_device it's enclosed in.
  56 */
  57#define to_lgdev(vd) container_of(vd, struct lguest_device, vdev)
  58
  59/*D:130
  60 * Device configurations
  61 *
  62 * The configuration information for a device consists of one or more
  63 * virtqueues, a feature bitmap, and some configuration bytes.  The
  64 * configuration bytes don't really matter to us: the Launcher sets them up, and
  65 * the driver will look at them during setup.
  66 *
  67 * A convenient routine to return the device's virtqueue config array:
  68 * immediately after the descriptor.
  69 */
  70static struct lguest_vqconfig *lg_vq(const struct lguest_device_desc *desc)
  71{
  72        return (void *)(desc + 1);
  73}
  74
  75/* The features come immediately after the virtqueues. */
  76static u8 *lg_features(const struct lguest_device_desc *desc)
  77{
  78        return (void *)(lg_vq(desc) + desc->num_vq);
  79}
  80
  81/* The config space comes after the two feature bitmasks. */
  82static u8 *lg_config(const struct lguest_device_desc *desc)
  83{
  84        return lg_features(desc) + desc->feature_len * 2;
  85}
  86
  87/* The total size of the config page used by this device (incl. desc) */
  88static unsigned desc_size(const struct lguest_device_desc *desc)
  89{
  90        return sizeof(*desc)
  91                + desc->num_vq * sizeof(struct lguest_vqconfig)
  92                + desc->feature_len * 2
  93                + desc->config_len;
  94}
  95
  96/* This gets the device's feature bits. */
  97static u32 lg_get_features(struct virtio_device *vdev)
  98{
  99        unsigned int i;
 100        u32 features = 0;
 101        struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
 102        u8 *in_features = lg_features(desc);
 103
 104        /* We do this the slow but generic way. */
 105        for (i = 0; i < min(desc->feature_len * 8, 32); i++)
 106                if (in_features[i / 8] & (1 << (i % 8)))
 107                        features |= (1 << i);
 108
 109        return features;
 110}
 111
 112/*
 113 * To notify on reset or feature finalization, we (ab)use the NOTIFY
 114 * hypercall, with the descriptor address of the device.
 115 */
 116static void status_notify(struct virtio_device *vdev)
 117{
 118        unsigned long offset = (void *)to_lgdev(vdev)->desc - lguest_devices;
 119
 120        hcall(LHCALL_NOTIFY, (max_pfn << PAGE_SHIFT) + offset, 0, 0, 0);
 121}
 122
 123/*
 124 * The virtio core takes the features the Host offers, and copies the ones
 125 * supported by the driver into the vdev->features array.  Once that's all
 126 * sorted out, this routine is called so we can tell the Host which features we
 127 * understand and accept.
 128 */
 129static void lg_finalize_features(struct virtio_device *vdev)
 130{
 131        unsigned int i, bits;
 132        struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
 133        /* Second half of bitmap is features we accept. */
 134        u8 *out_features = lg_features(desc) + desc->feature_len;
 135
 136        /* Give virtio_ring a chance to accept features. */
 137        vring_transport_features(vdev);
 138
 139        /*
 140         * The vdev->feature array is a Linux bitmask: this isn't the same as a
 141         * the simple array of bits used by lguest devices for features.  So we
 142         * do this slow, manual conversion which is completely general.
 143         */
 144        memset(out_features, 0, desc->feature_len);
 145        bits = min_t(unsigned, desc->feature_len, sizeof(vdev->features)) * 8;
 146        for (i = 0; i < bits; i++) {
 147                if (test_bit(i, vdev->features))
 148                        out_features[i / 8] |= (1 << (i % 8));
 149        }
 150
 151        /* Tell Host we've finished with this device's feature negotiation */
 152        status_notify(vdev);
 153}
 154
 155/* Once they've found a field, getting a copy of it is easy. */
 156static void lg_get(struct virtio_device *vdev, unsigned int offset,
 157                   void *buf, unsigned len)
 158{
 159        struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
 160
 161        /* Check they didn't ask for more than the length of the config! */
 162        BUG_ON(offset + len > desc->config_len);
 163        memcpy(buf, lg_config(desc) + offset, len);
 164}
 165
 166/* Setting the contents is also trivial. */
 167static void lg_set(struct virtio_device *vdev, unsigned int offset,
 168                   const void *buf, unsigned len)
 169{
 170        struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
 171
 172        /* Check they didn't ask for more than the length of the config! */
 173        BUG_ON(offset + len > desc->config_len);
 174        memcpy(lg_config(desc) + offset, buf, len);
 175}
 176
 177/*
 178 * The operations to get and set the status word just access the status field
 179 * of the device descriptor.
 180 */
 181static u8 lg_get_status(struct virtio_device *vdev)
 182{
 183        return to_lgdev(vdev)->desc->status;
 184}
 185
 186static void lg_set_status(struct virtio_device *vdev, u8 status)
 187{
 188        BUG_ON(!status);
 189        to_lgdev(vdev)->desc->status = status;
 190
 191        /* Tell Host immediately if we failed. */
 192        if (status & VIRTIO_CONFIG_S_FAILED)
 193                status_notify(vdev);
 194}
 195
 196static void lg_reset(struct virtio_device *vdev)
 197{
 198        /* 0 status means "reset" */
 199        to_lgdev(vdev)->desc->status = 0;
 200        status_notify(vdev);
 201}
 202
 203/*
 204 * Virtqueues
 205 *
 206 * The other piece of infrastructure virtio needs is a "virtqueue": a way of
 207 * the Guest device registering buffers for the other side to read from or
 208 * write into (ie. send and receive buffers).  Each device can have multiple
 209 * virtqueues: for example the console driver uses one queue for sending and
 210 * another for receiving.
 211 *
 212 * Fortunately for us, a very fast shared-memory-plus-descriptors virtqueue
 213 * already exists in virtio_ring.c.  We just need to connect it up.
 214 *
 215 * We start with the information we need to keep about each virtqueue.
 216 */
 217
 218/*D:140 This is the information we remember about each virtqueue. */
 219struct lguest_vq_info {
 220        /* A copy of the information contained in the device config. */
 221        struct lguest_vqconfig config;
 222
 223        /* The address where we mapped the virtio ring, so we can unmap it. */
 224        void *pages;
 225};
 226
 227/*
 228 * When the virtio_ring code wants to prod the Host, it calls us here and we
 229 * make a hypercall.  We hand the physical address of the virtqueue so the Host
 230 * knows which virtqueue we're talking about.
 231 */
 232static void lg_notify(struct virtqueue *vq)
 233{
 234        /*
 235         * We store our virtqueue information in the "priv" pointer of the
 236         * virtqueue structure.
 237         */
 238        struct lguest_vq_info *lvq = vq->priv;
 239
 240        hcall(LHCALL_NOTIFY, lvq->config.pfn << PAGE_SHIFT, 0, 0, 0);
 241}
 242
 243/* An extern declaration inside a C file is bad form.  Don't do it. */
 244extern int lguest_setup_irq(unsigned int irq);
 245
 246/*
 247 * This routine finds the Nth virtqueue described in the configuration of
 248 * this device and sets it up.
 249 *
 250 * This is kind of an ugly duckling.  It'd be nicer to have a standard
 251 * representation of a virtqueue in the configuration space, but it seems that
 252 * everyone wants to do it differently.  The KVM coders want the Guest to
 253 * allocate its own pages and tell the Host where they are, but for lguest it's
 254 * simpler for the Host to simply tell us where the pages are.
 255 */
 256static struct virtqueue *lg_find_vq(struct virtio_device *vdev,
 257                                    unsigned index,
 258                                    void (*callback)(struct virtqueue *vq),
 259                                    const char *name)
 260{
 261        struct lguest_device *ldev = to_lgdev(vdev);
 262        struct lguest_vq_info *lvq;
 263        struct virtqueue *vq;
 264        int err;
 265
 266        /* We must have this many virtqueues. */
 267        if (index >= ldev->desc->num_vq)
 268                return ERR_PTR(-ENOENT);
 269
 270        lvq = kmalloc(sizeof(*lvq), GFP_KERNEL);
 271        if (!lvq)
 272                return ERR_PTR(-ENOMEM);
 273
 274        /*
 275         * Make a copy of the "struct lguest_vqconfig" entry, which sits after
 276         * the descriptor.  We need a copy because the config space might not
 277         * be aligned correctly.
 278         */
 279        memcpy(&lvq->config, lg_vq(ldev->desc)+index, sizeof(lvq->config));
 280
 281        printk("Mapping virtqueue %i addr %lx\n", index,
 282               (unsigned long)lvq->config.pfn << PAGE_SHIFT);
 283        /* Figure out how many pages the ring will take, and map that memory */
 284        lvq->pages = lguest_map((unsigned long)lvq->config.pfn << PAGE_SHIFT,
 285                                DIV_ROUND_UP(vring_size(lvq->config.num,
 286                                                        LGUEST_VRING_ALIGN),
 287                                             PAGE_SIZE));
 288        if (!lvq->pages) {
 289                err = -ENOMEM;
 290                goto free_lvq;
 291        }
 292
 293        /*
 294         * OK, tell virtio_ring.c to set up a virtqueue now we know its size
 295         * and we've got a pointer to its pages.  Note that we set weak_barriers
 296         * to 'true': the host just a(nother) SMP CPU, so we only need inter-cpu
 297         * barriers.
 298         */
 299        vq = vring_new_virtqueue(lvq->config.num, LGUEST_VRING_ALIGN, vdev,
 300                                 true, lvq->pages, lg_notify, callback, name);
 301        if (!vq) {
 302                err = -ENOMEM;
 303                goto unmap;
 304        }
 305
 306        /* Make sure the interrupt is allocated. */
 307        err = lguest_setup_irq(lvq->config.irq);
 308        if (err)
 309                goto destroy_vring;
 310
 311        /*
 312         * Tell the interrupt for this virtqueue to go to the virtio_ring
 313         * interrupt handler.
 314         *
 315         * FIXME: We used to have a flag for the Host to tell us we could use
 316         * the interrupt as a source of randomness: it'd be nice to have that
 317         * back.
 318         */
 319        err = request_irq(lvq->config.irq, vring_interrupt, IRQF_SHARED,
 320                          dev_name(&vdev->dev), vq);
 321        if (err)
 322                goto free_desc;
 323
 324        /*
 325         * Last of all we hook up our 'struct lguest_vq_info" to the
 326         * virtqueue's priv pointer.
 327         */
 328        vq->priv = lvq;
 329        return vq;
 330
 331free_desc:
 332        irq_free_desc(lvq->config.irq);
 333destroy_vring:
 334        vring_del_virtqueue(vq);
 335unmap:
 336        lguest_unmap(lvq->pages);
 337free_lvq:
 338        kfree(lvq);
 339        return ERR_PTR(err);
 340}
 341/*:*/
 342
 343/* Cleaning up a virtqueue is easy */
 344static void lg_del_vq(struct virtqueue *vq)
 345{
 346        struct lguest_vq_info *lvq = vq->priv;
 347
 348        /* Release the interrupt */
 349        free_irq(lvq->config.irq, vq);
 350        /* Tell virtio_ring.c to free the virtqueue. */
 351        vring_del_virtqueue(vq);
 352        /* Unmap the pages containing the ring. */
 353        lguest_unmap(lvq->pages);
 354        /* Free our own queue information. */
 355        kfree(lvq);
 356}
 357
 358static void lg_del_vqs(struct virtio_device *vdev)
 359{
 360        struct virtqueue *vq, *n;
 361
 362        list_for_each_entry_safe(vq, n, &vdev->vqs, list)
 363                lg_del_vq(vq);
 364}
 365
 366static int lg_find_vqs(struct virtio_device *vdev, unsigned nvqs,
 367                       struct virtqueue *vqs[],
 368                       vq_callback_t *callbacks[],
 369                       const char *names[])
 370{
 371        struct lguest_device *ldev = to_lgdev(vdev);
 372        int i;
 373
 374        /* We must have this many virtqueues. */
 375        if (nvqs > ldev->desc->num_vq)
 376                return -ENOENT;
 377
 378        for (i = 0; i < nvqs; ++i) {
 379                vqs[i] = lg_find_vq(vdev, i, callbacks[i], names[i]);
 380                if (IS_ERR(vqs[i]))
 381                        goto error;
 382        }
 383        return 0;
 384
 385error:
 386        lg_del_vqs(vdev);
 387        return PTR_ERR(vqs[i]);
 388}
 389
 390static const char *lg_bus_name(struct virtio_device *vdev)
 391{
 392        return "";
 393}
 394
 395/* The ops structure which hooks everything together. */
 396static struct virtio_config_ops lguest_config_ops = {
 397        .get_features = lg_get_features,
 398        .finalize_features = lg_finalize_features,
 399        .get = lg_get,
 400        .set = lg_set,
 401        .get_status = lg_get_status,
 402        .set_status = lg_set_status,
 403        .reset = lg_reset,
 404        .find_vqs = lg_find_vqs,
 405        .del_vqs = lg_del_vqs,
 406        .bus_name = lg_bus_name,
 407};
 408
 409/*
 410 * The root device for the lguest virtio devices.  This makes them appear as
 411 * /sys/devices/lguest/0,1,2 not /sys/devices/0,1,2.
 412 */
 413static struct device *lguest_root;
 414
 415/*D:120
 416 * This is the core of the lguest bus: actually adding a new device.
 417 * It's a separate function because it's neater that way, and because an
 418 * earlier version of the code supported hotplug and unplug.  They were removed
 419 * early on because they were never used.
 420 *
 421 * As Andrew Tridgell says, "Untested code is buggy code".
 422 *
 423 * It's worth reading this carefully: we start with a pointer to the new device
 424 * descriptor in the "lguest_devices" page, and the offset into the device
 425 * descriptor page so we can uniquely identify it if things go badly wrong.
 426 */
 427static void add_lguest_device(struct lguest_device_desc *d,
 428                              unsigned int offset)
 429{
 430        struct lguest_device *ldev;
 431
 432        /* Start with zeroed memory; Linux's device layer counts on it. */
 433        ldev = kzalloc(sizeof(*ldev), GFP_KERNEL);
 434        if (!ldev) {
 435                printk(KERN_EMERG "Cannot allocate lguest dev %u type %u\n",
 436                       offset, d->type);
 437                return;
 438        }
 439
 440        /* This devices' parent is the lguest/ dir. */
 441        ldev->vdev.dev.parent = lguest_root;
 442        /*
 443         * The device type comes straight from the descriptor.  There's also a
 444         * device vendor field in the virtio_device struct, which we leave as
 445         * 0.
 446         */
 447        ldev->vdev.id.device = d->type;
 448        /*
 449         * We have a simple set of routines for querying the device's
 450         * configuration information and setting its status.
 451         */
 452        ldev->vdev.config = &lguest_config_ops;
 453        /* And we remember the device's descriptor for lguest_config_ops. */
 454        ldev->desc = d;
 455
 456        /*
 457         * register_virtio_device() sets up the generic fields for the struct
 458         * virtio_device and calls device_register().  This makes the bus
 459         * infrastructure look for a matching driver.
 460         */
 461        if (register_virtio_device(&ldev->vdev) != 0) {
 462                printk(KERN_ERR "Failed to register lguest dev %u type %u\n",
 463                       offset, d->type);
 464                kfree(ldev);
 465        }
 466}
 467
 468/*D:110
 469 * scan_devices() simply iterates through the device page.  The type 0 is
 470 * reserved to mean "end of devices".
 471 */
 472static void scan_devices(void)
 473{
 474        unsigned int i;
 475        struct lguest_device_desc *d;
 476
 477        /* We start at the page beginning, and skip over each entry. */
 478        for (i = 0; i < PAGE_SIZE; i += desc_size(d)) {
 479                d = lguest_devices + i;
 480
 481                /* Once we hit a zero, stop. */
 482                if (d->type == 0)
 483                        break;
 484
 485                printk("Device at %i has size %u\n", i, desc_size(d));
 486                add_lguest_device(d, i);
 487        }
 488}
 489
 490/*D:105
 491 * Fairly early in boot, lguest_devices_init() is called to set up the
 492 * lguest device infrastructure.  We check that we are a Guest by checking
 493 * pv_info.name: there are other ways of checking, but this seems most
 494 * obvious to me.
 495 *
 496 * So we can access the "struct lguest_device_desc"s easily, we map that memory
 497 * and store the pointer in the global "lguest_devices".  Then we register a
 498 * root device from which all our devices will hang (this seems to be the
 499 * correct sysfs incantation).
 500 *
 501 * Finally we call scan_devices() which adds all the devices found in the
 502 * lguest_devices page.
 503 */
 504static int __init lguest_devices_init(void)
 505{
 506        if (strcmp(pv_info.name, "lguest") != 0)
 507                return 0;
 508
 509        lguest_root = root_device_register("lguest");
 510        if (IS_ERR(lguest_root))
 511                panic("Could not register lguest root");
 512
 513        /* Devices are in a single page above top of "normal" mem */
 514        lguest_devices = lguest_map(max_pfn<<PAGE_SHIFT, 1);
 515
 516        scan_devices();
 517        return 0;
 518}
 519/* We do this after core stuff, but before the drivers. */
 520postcore_initcall(lguest_devices_init);
 521
 522/*D:150
 523 * At this point in the journey we used to now wade through the lguest
 524 * devices themselves: net, block and console.  Since they're all now virtio
 525 * devices rather than lguest-specific, I've decided to ignore them.  Mostly,
 526 * they're kind of boring.  But this does mean you'll never experience the
 527 * thrill of reading the forbidden love scene buried deep in the block driver.
 528 *
 529 * "make Launcher" beckons, where we answer questions like "Where do Guests
 530 * come from?", and "What do you do when someone asks for optimization?".
 531 */
 532
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