Root/drivers/lguest/lguest_device.c

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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