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        if (!name)
 267                return NULL;
 268
 269        /* We must have this many virtqueues. */
 270        if (index >= ldev->desc->num_vq)
 271                return ERR_PTR(-ENOENT);
 272
 273        lvq = kmalloc(sizeof(*lvq), GFP_KERNEL);
 274        if (!lvq)
 275                return ERR_PTR(-ENOMEM);
 276
 277        /*
 278         * Make a copy of the "struct lguest_vqconfig" entry, which sits after
 279         * the descriptor.  We need a copy because the config space might not
 280         * be aligned correctly.
 281         */
 282        memcpy(&lvq->config, lg_vq(ldev->desc)+index, sizeof(lvq->config));
 283
 284        printk("Mapping virtqueue %i addr %lx\n", index,
 285               (unsigned long)lvq->config.pfn << PAGE_SHIFT);
 286        /* Figure out how many pages the ring will take, and map that memory */
 287        lvq->pages = lguest_map((unsigned long)lvq->config.pfn << PAGE_SHIFT,
 288                                DIV_ROUND_UP(vring_size(lvq->config.num,
 289                                                        LGUEST_VRING_ALIGN),
 290                                             PAGE_SIZE));
 291        if (!lvq->pages) {
 292                err = -ENOMEM;
 293                goto free_lvq;
 294        }
 295
 296        /*
 297         * OK, tell virtio_ring.c to set up a virtqueue now we know its size
 298         * and we've got a pointer to its pages.  Note that we set weak_barriers
 299         * to 'true': the host just a(nother) SMP CPU, so we only need inter-cpu
 300         * barriers.
 301         */
 302        vq = vring_new_virtqueue(index, lvq->config.num, LGUEST_VRING_ALIGN, vdev,
 303                                 true, lvq->pages, lg_notify, callback, name);
 304        if (!vq) {
 305                err = -ENOMEM;
 306                goto unmap;
 307        }
 308
 309        /* Make sure the interrupt is allocated. */
 310        err = lguest_setup_irq(lvq->config.irq);
 311        if (err)
 312                goto destroy_vring;
 313
 314        /*
 315         * Tell the interrupt for this virtqueue to go to the virtio_ring
 316         * interrupt handler.
 317         *
 318         * FIXME: We used to have a flag for the Host to tell us we could use
 319         * the interrupt as a source of randomness: it'd be nice to have that
 320         * back.
 321         */
 322        err = request_irq(lvq->config.irq, vring_interrupt, IRQF_SHARED,
 323                          dev_name(&vdev->dev), vq);
 324        if (err)
 325                goto free_desc;
 326
 327        /*
 328         * Last of all we hook up our 'struct lguest_vq_info" to the
 329         * virtqueue's priv pointer.
 330         */
 331        vq->priv = lvq;
 332        return vq;
 333
 334free_desc:
 335        irq_free_desc(lvq->config.irq);
 336destroy_vring:
 337        vring_del_virtqueue(vq);
 338unmap:
 339        lguest_unmap(lvq->pages);
 340free_lvq:
 341        kfree(lvq);
 342        return ERR_PTR(err);
 343}
 344/*:*/
 345
 346/* Cleaning up a virtqueue is easy */
 347static void lg_del_vq(struct virtqueue *vq)
 348{
 349        struct lguest_vq_info *lvq = vq->priv;
 350
 351        /* Release the interrupt */
 352        free_irq(lvq->config.irq, vq);
 353        /* Tell virtio_ring.c to free the virtqueue. */
 354        vring_del_virtqueue(vq);
 355        /* Unmap the pages containing the ring. */
 356        lguest_unmap(lvq->pages);
 357        /* Free our own queue information. */
 358        kfree(lvq);
 359}
 360
 361static void lg_del_vqs(struct virtio_device *vdev)
 362{
 363        struct virtqueue *vq, *n;
 364
 365        list_for_each_entry_safe(vq, n, &vdev->vqs, list)
 366                lg_del_vq(vq);
 367}
 368
 369static int lg_find_vqs(struct virtio_device *vdev, unsigned nvqs,
 370                       struct virtqueue *vqs[],
 371                       vq_callback_t *callbacks[],
 372                       const char *names[])
 373{
 374        struct lguest_device *ldev = to_lgdev(vdev);
 375        int i;
 376
 377        /* We must have this many virtqueues. */
 378        if (nvqs > ldev->desc->num_vq)
 379                return -ENOENT;
 380
 381        for (i = 0; i < nvqs; ++i) {
 382                vqs[i] = lg_find_vq(vdev, i, callbacks[i], names[i]);
 383                if (IS_ERR(vqs[i]))
 384                        goto error;
 385        }
 386        return 0;
 387
 388error:
 389        lg_del_vqs(vdev);
 390        return PTR_ERR(vqs[i]);
 391}
 392
 393static const char *lg_bus_name(struct virtio_device *vdev)
 394{
 395        return "";
 396}
 397
 398/* The ops structure which hooks everything together. */
 399static struct virtio_config_ops lguest_config_ops = {
 400        .get_features = lg_get_features,
 401        .finalize_features = lg_finalize_features,
 402        .get = lg_get,
 403        .set = lg_set,
 404        .get_status = lg_get_status,
 405        .set_status = lg_set_status,
 406        .reset = lg_reset,
 407        .find_vqs = lg_find_vqs,
 408        .del_vqs = lg_del_vqs,
 409        .bus_name = lg_bus_name,
 410};
 411
 412/*
 413 * The root device for the lguest virtio devices.  This makes them appear as
 414 * /sys/devices/lguest/0,1,2 not /sys/devices/0,1,2.
 415 */
 416static struct device *lguest_root;
 417
 418/*D:120
 419 * This is the core of the lguest bus: actually adding a new device.
 420 * It's a separate function because it's neater that way, and because an
 421 * earlier version of the code supported hotplug and unplug.  They were removed
 422 * early on because they were never used.
 423 *
 424 * As Andrew Tridgell says, "Untested code is buggy code".
 425 *
 426 * It's worth reading this carefully: we start with a pointer to the new device
 427 * descriptor in the "lguest_devices" page, and the offset into the device
 428 * descriptor page so we can uniquely identify it if things go badly wrong.
 429 */
 430static void add_lguest_device(struct lguest_device_desc *d,
 431                              unsigned int offset)
 432{
 433        struct lguest_device *ldev;
 434
 435        /* Start with zeroed memory; Linux's device layer counts on it. */
 436        ldev = kzalloc(sizeof(*ldev), GFP_KERNEL);
 437        if (!ldev) {
 438                printk(KERN_EMERG "Cannot allocate lguest dev %u type %u\n",
 439                       offset, d->type);
 440                return;
 441        }
 442
 443        /* This devices' parent is the lguest/ dir. */
 444        ldev->vdev.dev.parent = lguest_root;
 445        /*
 446         * The device type comes straight from the descriptor.  There's also a
 447         * device vendor field in the virtio_device struct, which we leave as
 448         * 0.
 449         */
 450        ldev->vdev.id.device = d->type;
 451        /*
 452         * We have a simple set of routines for querying the device's
 453         * configuration information and setting its status.
 454         */
 455        ldev->vdev.config = &lguest_config_ops;
 456        /* And we remember the device's descriptor for lguest_config_ops. */
 457        ldev->desc = d;
 458
 459        /*
 460         * register_virtio_device() sets up the generic fields for the struct
 461         * virtio_device and calls device_register().  This makes the bus
 462         * infrastructure look for a matching driver.
 463         */
 464        if (register_virtio_device(&ldev->vdev) != 0) {
 465                printk(KERN_ERR "Failed to register lguest dev %u type %u\n",
 466                       offset, d->type);
 467                kfree(ldev);
 468        }
 469}
 470
 471/*D:110
 472 * scan_devices() simply iterates through the device page.  The type 0 is
 473 * reserved to mean "end of devices".
 474 */
 475static void scan_devices(void)
 476{
 477        unsigned int i;
 478        struct lguest_device_desc *d;
 479
 480        /* We start at the page beginning, and skip over each entry. */
 481        for (i = 0; i < PAGE_SIZE; i += desc_size(d)) {
 482                d = lguest_devices + i;
 483
 484                /* Once we hit a zero, stop. */
 485                if (d->type == 0)
 486                        break;
 487
 488                printk("Device at %i has size %u\n", i, desc_size(d));
 489                add_lguest_device(d, i);
 490        }
 491}
 492
 493/*D:105
 494 * Fairly early in boot, lguest_devices_init() is called to set up the
 495 * lguest device infrastructure.  We check that we are a Guest by checking
 496 * pv_info.name: there are other ways of checking, but this seems most
 497 * obvious to me.
 498 *
 499 * So we can access the "struct lguest_device_desc"s easily, we map that memory
 500 * and store the pointer in the global "lguest_devices".  Then we register a
 501 * root device from which all our devices will hang (this seems to be the
 502 * correct sysfs incantation).
 503 *
 504 * Finally we call scan_devices() which adds all the devices found in the
 505 * lguest_devices page.
 506 */
 507static int __init lguest_devices_init(void)
 508{
 509        if (strcmp(pv_info.name, "lguest") != 0)
 510                return 0;
 511
 512        lguest_root = root_device_register("lguest");
 513        if (IS_ERR(lguest_root))
 514                panic("Could not register lguest root");
 515
 516        /* Devices are in a single page above top of "normal" mem */
 517        lguest_devices = lguest_map(max_pfn<<PAGE_SHIFT, 1);
 518
 519        scan_devices();
 520        return 0;
 521}
 522/* We do this after core stuff, but before the drivers. */
 523postcore_initcall(lguest_devices_init);
 524
 525/*D:150
 526 * At this point in the journey we used to now wade through the lguest
 527 * devices themselves: net, block and console.  Since they're all now virtio
 528 * devices rather than lguest-specific, I've decided to ignore them.  Mostly,
 529 * they're kind of boring.  But this does mean you'll never experience the
 530 * thrill of reading the forbidden love scene buried deep in the block driver.
 531 *
 532 * "make Launcher" beckons, where we answer questions like "Where do Guests
 533 * come from?", and "What do you do when someone asks for optimization?".
 534 */
 535
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