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"
18
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.
23 *
24 * The notification value is in cpu->pending_notify: we return true if it went
25 * to an eventfd.
26 */
27bool send_notify_to_eventfd(struct lg_cpu *cpu)
28{
29	unsigned int i;
30	struct lg_eventfd_map *map;
31
32	/*
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?)
37	 */
38	rcu_read_lock();
39	/*
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
46	 *
47	 * So play safe, use rcu_dereference to get the rcu-protected pointer:
48	 */
49	map = rcu_dereference(cpu->lg->eventfds);
50	/*
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.
53	 */
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;
59		}
60	}
61	/* We're done with the rcu-protected variable cpu->lg->eventfds. */
62	rcu_read_unlock();
63
64	/* If we cleared the notification, it's because we found a match. */
65	return cpu->pending_notify == 0;
66}
67
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).
74 *
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.
80 *
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.
87 *
88 * If that's unclear, see http://en.wikipedia.org/wiki/Read-copy-update.
89 */
90static int add_eventfd(struct lguest *lg, unsigned long addr, int fd)
91{
92	struct lg_eventfd_map *new, *old = lg->eventfds;
93
94	/*
95	 * We don't allow notifications on value 0 anyway (pending_notify of
96	 * 0 means "nothing pending").
97	 */
98	if (!addr)
99		return -EINVAL;
100
101	/*
102	 * Replace the old array with the new one, carefully: others can
103	 * be accessing it at the same time.
104	 */
105	new = kmalloc(sizeof(*new) + sizeof(new->map[0]) * (old->num + 1),
106		      GFP_KERNEL);
107	if (!new)
108		return -ENOMEM;
109
110	/* First make identical copy. */
111	memcpy(new->map, old->map, sizeof(old->map[0]) * old->num);
112	new->num = old->num;
113
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;
121	}
122	new->num++;
123
124	/*
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.
129	 *
130	 * We have to think about these kinds of things when we're operating on
131	 * live data without locks.
132	 */
133	rcu_assign_pointer(lg->eventfds, new);
134
135	/*
136	 * We're not in a big hurry.  Wait until no one's looking at old
137	 * version, then free it.
138	 */
139	synchronize_rcu();
140	kfree(old);
141
142	return 0;
143}
144
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.
149 *
150 * This is really convenient for processing each virtqueue in a separate
151 * thread.
152 */
153static int attach_eventfd(struct lguest *lg, const unsigned long __user *input)
154{
155	unsigned long addr, fd;
156	int err;
157
158	if (get_user(addr, input) != 0)
159		return -EFAULT;
160	input++;
161	if (get_user(fd, input) != 0)
162		return -EFAULT;
163
164	/*
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.
168	 */
169	mutex_lock(&lguest_lock);
170	err = add_eventfd(lg, addr, fd);
171	mutex_unlock(&lguest_lock);
172
173	return err;
174}
175
176/*L:050
177 * Sending an interrupt is done by writing LHREQ_IRQ and an interrupt
178 * number to /dev/lguest.
179 */
180static int user_send_irq(struct lg_cpu *cpu, const unsigned long __user *input)
181{
182	unsigned long irq;
183
184	if (get_user(irq, input) != 0)
185		return -EFAULT;
186	if (irq >= LGUEST_IRQS)
187		return -EINVAL;
188
189	/*
190	 * Next time the Guest runs, the core code will see if it can deliver
191	 * this interrupt.
192	 */
193	set_interrupt(cpu, irq);
194	return 0;
195}
196
197/*L:040
198 * Once our Guest is initialized, the Launcher makes it run by reading
199 * from /dev/lguest.
200 */
201static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
202{
203	struct lguest *lg = file->private_data;
204	struct lg_cpu *cpu;
205	unsigned int cpu_id = *o;
206
207	/* You must write LHREQ_INITIALIZE first! */
208	if (!lg)
209		return -EINVAL;
210
211	/* Watch out for arbitrary vcpu indexes! */
212	if (cpu_id >= lg->nr_cpus)
213		return -EINVAL;
214
215	cpu = &lg->cpus[cpu_id];
216
217	/* If you're not the task which owns the Guest, go away. */
218	if (current != cpu->tsk)
219		return -EPERM;
220
221	/* If the Guest is already dead, we indicate why */
222	if (lg->dead) {
223		size_t len;
224
225		/* lg->dead either contains an error code, or a string. */
226		if (IS_ERR(lg->dead))
227			return PTR_ERR(lg->dead);
228
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;
234	}
235
236	/*
237	 * If we returned from read() last time because the Guest sent I/O,
238	 * clear the flag.
239	 */
240	if (cpu->pending_notify)
241		cpu->pending_notify = 0;
242
243	/* Run the Guest until something interesting happens. */
244	return run_guest(cpu, (unsigned long __user *)user);
245}
246
247/*L:025
248 * This actually initializes a CPU.  For the moment, a Guest is only
249 * uniprocessor, so "id" is always 0.
250 */
251static int lg_cpu_start(struct lg_cpu *cpu, unsigned id, unsigned long start_ip)
252{
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;
256
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++;
261
262	/* Each CPU has a timer it can set. */
263	init_clockdev(cpu);
264
265	/*
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.
268	 */
269	cpu->regs_page = get_zeroed_page(GFP_KERNEL);
270	if (!cpu->regs_page)
271		return -ENOMEM;
272
273	/* We actually put the registers at the bottom of the page. */
274	cpu->regs = (void *)cpu->regs_page + PAGE_SIZE - sizeof(*cpu->regs);
275
276	/*
277	 * Now we initialize the Guest's registers, handing it the start
278	 * address.
279	 */
280	lguest_arch_setup_regs(cpu, start_ip);
281
282	/*
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).
285	 */
286	cpu->tsk = current;
287
288	/*
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.
292	 */
293	cpu->mm = get_task_mm(cpu->tsk);
294
295	/*
296	 * We remember which CPU's pages this Guest used last, for optimization
297	 * when the same Guest runs on the same CPU twice.
298	 */
299	cpu->last_pages = NULL;
300
301	/* No error == success. */
302	return 0;
303}
304
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:
308 *
309 * base: The start of the Guest-physical memory inside the Launcher memory.
310 *
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.
314 *
315 * start: The first instruction to execute ("eip" in x86-speak).
316 */
317static int initialize(struct file *file, const unsigned long __user *input)
318{
319	/* "struct lguest" contains all we (the Host) know about a Guest. */
320	struct lguest *lg;
321	int err;
322	unsigned long args[3];
323
324	/*
325	 * We grab the Big Lguest lock, which protects against multiple
326	 * simultaneous initializations.
327	 */
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;
333	}
334
335	if (copy_from_user(args, input, sizeof(args)) != 0) {
336		err = -EFAULT;
337		goto unlock;
338	}
339
340	lg = kzalloc(sizeof(*lg), GFP_KERNEL);
341	if (!lg) {
342		err = -ENOMEM;
343		goto unlock;
344	}
345
346	lg->eventfds = kmalloc(sizeof(*lg->eventfds), GFP_KERNEL);
347	if (!lg->eventfds) {
348		err = -ENOMEM;
349		goto free_lg;
350	}
351	lg->eventfds->num = 0;
352
353	/* Populate the easy fields of our "struct lguest" */
354	lg->mem_base = (void __user *)args[0];
355	lg->pfn_limit = args[1];
356
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;
361
362	/*
363	 * Initialize the Guest's shadow page tables.  This allocates
364	 * memory, so can fail.
365	 */
366	err = init_guest_pagetable(lg);
367	if (err)
368		goto free_regs;
369
370	/* We keep our "struct lguest" in the file's private_data. */
371	file->private_data = lg;
372
373	mutex_unlock(&lguest_lock);
374
375	/* And because this is a write() call, we return the length used. */
376	return sizeof(args);
377
378free_regs:
379	/* FIXME: This should be in free_vcpu */
380	free_page(lg->cpus[0].regs_page);
381free_eventfds:
382	kfree(lg->eventfds);
383free_lg:
384	kfree(lg);
385unlock:
386	mutex_unlock(&lguest_lock);
387	return err;
388}
389
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.
395 *
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.
400 */
401static ssize_t write(struct file *file, const char __user *in,
402		     size_t size, loff_t *off)
403{
404	/*
405	 * Once the Guest is initialized, we hold the "struct lguest" in the
406	 * file private data.
407	 */
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;
413
414	/* The first value tells us what this request is. */
415	if (get_user(req, input) != 0)
416		return -EFAULT;
417	input++;
418
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];
424
425		/* Once the Guest is dead, you can only read() why it died. */
426		if (lg->dead)
427			return -ENOENT;
428	}
429
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;
439	}
440}
441
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.
446 *
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.
450:*/
451static int close(struct inode *inode, struct file *file)
452{
453	struct lguest *lg = file->private_data;
454	unsigned int i;
455
456	/* If we never successfully initialized, there's nothing to clean up */
457	if (!lg)
458		return 0;
459
460	/*
461	 * We need the big lock, to protect from inter-guest I/O and other
462	 * Launchers initializing guests.
463	 */
464	mutex_lock(&lguest_lock);
465
466	/* Free up the shadow page tables for the Guest. */
467	free_guest_pagetable(lg);
468
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);
474		/*
475		 * Now all the memory cleanups are done, it's safe to release
476		 * the Launcher's memory management structure.
477		 */
478		mmput(lg->cpus[i].mm);
479	}
480
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);
485
486	/*
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().
489	 */
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);
496
497	return 0;
498}
499
500/*L:000
501 * Welcome to our journey through the Launcher!
502 *
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.
507 *
508 * Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we
509 * shall see more of that later.
510 *
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:
514 */
515static const struct file_operations lguest_fops = {
516	.owner	 = THIS_MODULE,
517	.release = close,
518	.write	 = write,
519	.read	 = read,
520	.llseek  = default_llseek,
521};
522/*:*/
523
524/*
525 * This is a textbook example of a "misc" character device.  Populate a "struct
526 * miscdevice" and register it with misc_register().
527 */
528static struct miscdevice lguest_dev = {
529	.minor	= MISC_DYNAMIC_MINOR,
530	.name	= "lguest",
531	.fops	= &lguest_fops,
532};
533
534int __init lguest_device_init(void)
535{
536	return misc_register(&lguest_dev);
537}
538
539void __exit lguest_device_remove(void)
540{
541	misc_deregister(&lguest_dev);
542}
543