Switched to async sending
[pohmelfs.git] / drivers / lguest / lguest_user.c
blobff4a0bc9904d0b79149d4ace4de5d8bf572b2bb8
1 /*P:200 This contains all the /dev/lguest code, whereby the userspace
2 * launcher controls and communicates with the Guest. For example,
3 * the first write will tell us the Guest's memory layout and entry
4 * point. A read will run the Guest until something happens, such as
5 * a signal or the Guest doing a NOTIFY out to the Launcher. There is
6 * also a way for the Launcher to attach eventfds to particular NOTIFY
7 * values instead of returning from the read() call.
8 :*/
9 #include <linux/uaccess.h>
10 #include <linux/miscdevice.h>
11 #include <linux/fs.h>
12 #include <linux/sched.h>
13 #include <linux/eventfd.h>
14 #include <linux/file.h>
15 #include <linux/slab.h>
16 #include <linux/export.h>
17 #include "lg.h"
19 /*L:056
20 * Before we move on, let's jump ahead and look at what the kernel does when
21 * it needs to look up the eventfds. That will complete our picture of how we
22 * use RCU.
24 * The notification value is in cpu->pending_notify: we return true if it went
25 * to an eventfd.
27 bool send_notify_to_eventfd(struct lg_cpu *cpu)
29 unsigned int i;
30 struct lg_eventfd_map *map;
33 * This "rcu_read_lock()" helps track when someone is still looking at
34 * the (RCU-using) eventfds array. It's not actually a lock at all;
35 * indeed it's a noop in many configurations. (You didn't expect me to
36 * explain all the RCU secrets here, did you?)
38 rcu_read_lock();
40 * rcu_dereference is the counter-side of rcu_assign_pointer(); it
41 * makes sure we don't access the memory pointed to by
42 * cpu->lg->eventfds before cpu->lg->eventfds is set. Sounds crazy,
43 * but Alpha allows this! Paul McKenney points out that a really
44 * aggressive compiler could have the same effect:
45 * http://lists.ozlabs.org/pipermail/lguest/2009-July/001560.html
47 * So play safe, use rcu_dereference to get the rcu-protected pointer:
49 map = rcu_dereference(cpu->lg->eventfds);
51 * Simple array search: even if they add an eventfd while we do this,
52 * we'll continue to use the old array and just won't see the new one.
54 for (i = 0; i < map->num; i++) {
55 if (map->map[i].addr == cpu->pending_notify) {
56 eventfd_signal(map->map[i].event, 1);
57 cpu->pending_notify = 0;
58 break;
61 /* We're done with the rcu-protected variable cpu->lg->eventfds. */
62 rcu_read_unlock();
64 /* If we cleared the notification, it's because we found a match. */
65 return cpu->pending_notify == 0;
68 /*L:055
69 * One of the more tricksy tricks in the Linux Kernel is a technique called
70 * Read Copy Update. Since one point of lguest is to teach lguest journeyers
71 * about kernel coding, I use it here. (In case you're curious, other purposes
72 * include learning about virtualization and instilling a deep appreciation for
73 * simplicity and puppies).
75 * We keep a simple array which maps LHCALL_NOTIFY values to eventfds, but we
76 * add new eventfds without ever blocking readers from accessing the array.
77 * The current Launcher only does this during boot, so that never happens. But
78 * Read Copy Update is cool, and adding a lock risks damaging even more puppies
79 * than this code does.
81 * We allocate a brand new one-larger array, copy the old one and add our new
82 * element. Then we make the lg eventfd pointer point to the new array.
83 * That's the easy part: now we need to free the old one, but we need to make
84 * sure no slow CPU somewhere is still looking at it. That's what
85 * synchronize_rcu does for us: waits until every CPU has indicated that it has
86 * moved on to know it's no longer using the old one.
88 * If that's unclear, see http://en.wikipedia.org/wiki/Read-copy-update.
90 static int add_eventfd(struct lguest *lg, unsigned long addr, int fd)
92 struct lg_eventfd_map *new, *old = lg->eventfds;
95 * We don't allow notifications on value 0 anyway (pending_notify of
96 * 0 means "nothing pending").
98 if (!addr)
99 return -EINVAL;
102 * Replace the old array with the new one, carefully: others can
103 * be accessing it at the same time.
105 new = kmalloc(sizeof(*new) + sizeof(new->map[0]) * (old->num + 1),
106 GFP_KERNEL);
107 if (!new)
108 return -ENOMEM;
110 /* First make identical copy. */
111 memcpy(new->map, old->map, sizeof(old->map[0]) * old->num);
112 new->num = old->num;
114 /* Now append new entry. */
115 new->map[new->num].addr = addr;
116 new->map[new->num].event = eventfd_ctx_fdget(fd);
117 if (IS_ERR(new->map[new->num].event)) {
118 int err = PTR_ERR(new->map[new->num].event);
119 kfree(new);
120 return err;
122 new->num++;
125 * Now put new one in place: rcu_assign_pointer() is a fancy way of
126 * doing "lg->eventfds = new", but it uses memory barriers to make
127 * absolutely sure that the contents of "new" written above is nailed
128 * down before we actually do the assignment.
130 * We have to think about these kinds of things when we're operating on
131 * live data without locks.
133 rcu_assign_pointer(lg->eventfds, new);
136 * We're not in a big hurry. Wait until no one's looking at old
137 * version, then free it.
139 synchronize_rcu();
140 kfree(old);
142 return 0;
145 /*L:052
146 * Receiving notifications from the Guest is usually done by attaching a
147 * particular LHCALL_NOTIFY value to an event filedescriptor. The eventfd will
148 * become readable when the Guest does an LHCALL_NOTIFY with that value.
150 * This is really convenient for processing each virtqueue in a separate
151 * thread.
153 static int attach_eventfd(struct lguest *lg, const unsigned long __user *input)
155 unsigned long addr, fd;
156 int err;
158 if (get_user(addr, input) != 0)
159 return -EFAULT;
160 input++;
161 if (get_user(fd, input) != 0)
162 return -EFAULT;
165 * Just make sure two callers don't add eventfds at once. We really
166 * only need to lock against callers adding to the same Guest, so using
167 * the Big Lguest Lock is overkill. But this is setup, not a fast path.
169 mutex_lock(&lguest_lock);
170 err = add_eventfd(lg, addr, fd);
171 mutex_unlock(&lguest_lock);
173 return err;
176 /*L:050
177 * Sending an interrupt is done by writing LHREQ_IRQ and an interrupt
178 * number to /dev/lguest.
180 static int user_send_irq(struct lg_cpu *cpu, const unsigned long __user *input)
182 unsigned long irq;
184 if (get_user(irq, input) != 0)
185 return -EFAULT;
186 if (irq >= LGUEST_IRQS)
187 return -EINVAL;
190 * Next time the Guest runs, the core code will see if it can deliver
191 * this interrupt.
193 set_interrupt(cpu, irq);
194 return 0;
197 /*L:040
198 * Once our Guest is initialized, the Launcher makes it run by reading
199 * from /dev/lguest.
201 static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
203 struct lguest *lg = file->private_data;
204 struct lg_cpu *cpu;
205 unsigned int cpu_id = *o;
207 /* You must write LHREQ_INITIALIZE first! */
208 if (!lg)
209 return -EINVAL;
211 /* Watch out for arbitrary vcpu indexes! */
212 if (cpu_id >= lg->nr_cpus)
213 return -EINVAL;
215 cpu = &lg->cpus[cpu_id];
217 /* If you're not the task which owns the Guest, go away. */
218 if (current != cpu->tsk)
219 return -EPERM;
221 /* If the Guest is already dead, we indicate why */
222 if (lg->dead) {
223 size_t len;
225 /* lg->dead either contains an error code, or a string. */
226 if (IS_ERR(lg->dead))
227 return PTR_ERR(lg->dead);
229 /* We can only return as much as the buffer they read with. */
230 len = min(size, strlen(lg->dead)+1);
231 if (copy_to_user(user, lg->dead, len) != 0)
232 return -EFAULT;
233 return len;
237 * If we returned from read() last time because the Guest sent I/O,
238 * clear the flag.
240 if (cpu->pending_notify)
241 cpu->pending_notify = 0;
243 /* Run the Guest until something interesting happens. */
244 return run_guest(cpu, (unsigned long __user *)user);
247 /*L:025
248 * This actually initializes a CPU. For the moment, a Guest is only
249 * uniprocessor, so "id" is always 0.
251 static int lg_cpu_start(struct lg_cpu *cpu, unsigned id, unsigned long start_ip)
253 /* We have a limited number the number of CPUs in the lguest struct. */
254 if (id >= ARRAY_SIZE(cpu->lg->cpus))
255 return -EINVAL;
257 /* Set up this CPU's id, and pointer back to the lguest struct. */
258 cpu->id = id;
259 cpu->lg = container_of((cpu - id), struct lguest, cpus[0]);
260 cpu->lg->nr_cpus++;
262 /* Each CPU has a timer it can set. */
263 init_clockdev(cpu);
266 * We need a complete page for the Guest registers: they are accessible
267 * to the Guest and we can only grant it access to whole pages.
269 cpu->regs_page = get_zeroed_page(GFP_KERNEL);
270 if (!cpu->regs_page)
271 return -ENOMEM;
273 /* We actually put the registers at the bottom of the page. */
274 cpu->regs = (void *)cpu->regs_page + PAGE_SIZE - sizeof(*cpu->regs);
277 * Now we initialize the Guest's registers, handing it the start
278 * address.
280 lguest_arch_setup_regs(cpu, start_ip);
283 * We keep a pointer to the Launcher task (ie. current task) for when
284 * other Guests want to wake this one (eg. console input).
286 cpu->tsk = current;
289 * We need to keep a pointer to the Launcher's memory map, because if
290 * the Launcher dies we need to clean it up. If we don't keep a
291 * reference, it is destroyed before close() is called.
293 cpu->mm = get_task_mm(cpu->tsk);
296 * We remember which CPU's pages this Guest used last, for optimization
297 * when the same Guest runs on the same CPU twice.
299 cpu->last_pages = NULL;
301 /* No error == success. */
302 return 0;
305 /*L:020
306 * The initialization write supplies 3 pointer sized (32 or 64 bit) values (in
307 * addition to the LHREQ_INITIALIZE value). These are:
309 * base: The start of the Guest-physical memory inside the Launcher memory.
311 * pfnlimit: The highest (Guest-physical) page number the Guest should be
312 * allowed to access. The Guest memory lives inside the Launcher, so it sets
313 * this to ensure the Guest can only reach its own memory.
315 * start: The first instruction to execute ("eip" in x86-speak).
317 static int initialize(struct file *file, const unsigned long __user *input)
319 /* "struct lguest" contains all we (the Host) know about a Guest. */
320 struct lguest *lg;
321 int err;
322 unsigned long args[3];
325 * We grab the Big Lguest lock, which protects against multiple
326 * simultaneous initializations.
328 mutex_lock(&lguest_lock);
329 /* You can't initialize twice! Close the device and start again... */
330 if (file->private_data) {
331 err = -EBUSY;
332 goto unlock;
335 if (copy_from_user(args, input, sizeof(args)) != 0) {
336 err = -EFAULT;
337 goto unlock;
340 lg = kzalloc(sizeof(*lg), GFP_KERNEL);
341 if (!lg) {
342 err = -ENOMEM;
343 goto unlock;
346 lg->eventfds = kmalloc(sizeof(*lg->eventfds), GFP_KERNEL);
347 if (!lg->eventfds) {
348 err = -ENOMEM;
349 goto free_lg;
351 lg->eventfds->num = 0;
353 /* Populate the easy fields of our "struct lguest" */
354 lg->mem_base = (void __user *)args[0];
355 lg->pfn_limit = args[1];
357 /* This is the first cpu (cpu 0) and it will start booting at args[2] */
358 err = lg_cpu_start(&lg->cpus[0], 0, args[2]);
359 if (err)
360 goto free_eventfds;
363 * Initialize the Guest's shadow page tables. This allocates
364 * memory, so can fail.
366 err = init_guest_pagetable(lg);
367 if (err)
368 goto free_regs;
370 /* We keep our "struct lguest" in the file's private_data. */
371 file->private_data = lg;
373 mutex_unlock(&lguest_lock);
375 /* And because this is a write() call, we return the length used. */
376 return sizeof(args);
378 free_regs:
379 /* FIXME: This should be in free_vcpu */
380 free_page(lg->cpus[0].regs_page);
381 free_eventfds:
382 kfree(lg->eventfds);
383 free_lg:
384 kfree(lg);
385 unlock:
386 mutex_unlock(&lguest_lock);
387 return err;
390 /*L:010
391 * The first operation the Launcher does must be a write. All writes
392 * start with an unsigned long number: for the first write this must be
393 * LHREQ_INITIALIZE to set up the Guest. After that the Launcher can use
394 * writes of other values to send interrupts or set up receipt of notifications.
396 * Note that we overload the "offset" in the /dev/lguest file to indicate what
397 * CPU number we're dealing with. Currently this is always 0 since we only
398 * support uniprocessor Guests, but you can see the beginnings of SMP support
399 * here.
401 static ssize_t write(struct file *file, const char __user *in,
402 size_t size, loff_t *off)
405 * Once the Guest is initialized, we hold the "struct lguest" in the
406 * file private data.
408 struct lguest *lg = file->private_data;
409 const unsigned long __user *input = (const unsigned long __user *)in;
410 unsigned long req;
411 struct lg_cpu *uninitialized_var(cpu);
412 unsigned int cpu_id = *off;
414 /* The first value tells us what this request is. */
415 if (get_user(req, input) != 0)
416 return -EFAULT;
417 input++;
419 /* If you haven't initialized, you must do that first. */
420 if (req != LHREQ_INITIALIZE) {
421 if (!lg || (cpu_id >= lg->nr_cpus))
422 return -EINVAL;
423 cpu = &lg->cpus[cpu_id];
425 /* Once the Guest is dead, you can only read() why it died. */
426 if (lg->dead)
427 return -ENOENT;
430 switch (req) {
431 case LHREQ_INITIALIZE:
432 return initialize(file, input);
433 case LHREQ_IRQ:
434 return user_send_irq(cpu, input);
435 case LHREQ_EVENTFD:
436 return attach_eventfd(lg, input);
437 default:
438 return -EINVAL;
442 /*L:060
443 * The final piece of interface code is the close() routine. It reverses
444 * everything done in initialize(). This is usually called because the
445 * Launcher exited.
447 * Note that the close routine returns 0 or a negative error number: it can't
448 * really fail, but it can whine. I blame Sun for this wart, and K&R C for
449 * letting them do it.
451 static int close(struct inode *inode, struct file *file)
453 struct lguest *lg = file->private_data;
454 unsigned int i;
456 /* If we never successfully initialized, there's nothing to clean up */
457 if (!lg)
458 return 0;
461 * We need the big lock, to protect from inter-guest I/O and other
462 * Launchers initializing guests.
464 mutex_lock(&lguest_lock);
466 /* Free up the shadow page tables for the Guest. */
467 free_guest_pagetable(lg);
469 for (i = 0; i < lg->nr_cpus; i++) {
470 /* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */
471 hrtimer_cancel(&lg->cpus[i].hrt);
472 /* We can free up the register page we allocated. */
473 free_page(lg->cpus[i].regs_page);
475 * Now all the memory cleanups are done, it's safe to release
476 * the Launcher's memory management structure.
478 mmput(lg->cpus[i].mm);
481 /* Release any eventfds they registered. */
482 for (i = 0; i < lg->eventfds->num; i++)
483 eventfd_ctx_put(lg->eventfds->map[i].event);
484 kfree(lg->eventfds);
487 * If lg->dead doesn't contain an error code it will be NULL or a
488 * kmalloc()ed string, either of which is ok to hand to kfree().
490 if (!IS_ERR(lg->dead))
491 kfree(lg->dead);
492 /* Free the memory allocated to the lguest_struct */
493 kfree(lg);
494 /* Release lock and exit. */
495 mutex_unlock(&lguest_lock);
497 return 0;
500 /*L:000
501 * Welcome to our journey through the Launcher!
503 * The Launcher is the Host userspace program which sets up, runs and services
504 * the Guest. In fact, many comments in the Drivers which refer to "the Host"
505 * doing things are inaccurate: the Launcher does all the device handling for
506 * the Guest, but the Guest can't know that.
508 * Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we
509 * shall see more of that later.
511 * We begin our understanding with the Host kernel interface which the Launcher
512 * uses: reading and writing a character device called /dev/lguest. All the
513 * work happens in the read(), write() and close() routines:
515 static const struct file_operations lguest_fops = {
516 .owner = THIS_MODULE,
517 .release = close,
518 .write = write,
519 .read = read,
520 .llseek = default_llseek,
522 /*:*/
525 * This is a textbook example of a "misc" character device. Populate a "struct
526 * miscdevice" and register it with misc_register().
528 static struct miscdevice lguest_dev = {
529 .minor = MISC_DYNAMIC_MINOR,
530 .name = "lguest",
531 .fops = &lguest_fops,
534 int __init lguest_device_init(void)
536 return misc_register(&lguest_dev);
539 void __exit lguest_device_remove(void)
541 misc_deregister(&lguest_dev);