aboutsummaryrefslogtreecommitdiff
path: root/drivers/lguest/lguest_user.c
blob: bcdcf3453e7811c264a2dc5b7eb76a1e57a2800d (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
/*P:200 This contains all the /dev/lguest code, whereby the userspace launcher
 * controls and communicates with the Guest.  For example, the first write will
 * tell us the Guest's memory layout, pagetable, entry point and kernel address
 * offset.  A read will run the Guest until something happens, such as a signal
 * or the Guest doing a NOTIFY out to the Launcher. :*/
#include <linux/uaccess.h>
#include <linux/miscdevice.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include "lg.h"

/*L:055 When something happens, the Waker process needs a way to stop the
 * kernel running the Guest and return to the Launcher.  So the Waker writes
 * LHREQ_BREAK and the value "1" to /dev/lguest to do this.  Once the Launcher
 * has done whatever needs attention, it writes LHREQ_BREAK and "0" to release
 * the Waker. */
static int break_guest_out(struct lg_cpu *cpu, const unsigned long __user*input)
{
	unsigned long on;

	/* Fetch whether they're turning break on or off. */
	if (get_user(on, input) != 0)
		return -EFAULT;

	if (on) {
		cpu->break_out = 1;
		if (!wake_up_process(cpu->tsk))
			kick_process(cpu->tsk);
		/* Wait for them to reset it */
		return wait_event_interruptible(cpu->break_wq, !cpu->break_out);
	} else {
		cpu->break_out = 0;
		wake_up(&cpu->break_wq);
		return 0;
	}
}

/*L:050 Sending an interrupt is done by writing LHREQ_IRQ and an interrupt
 * number to /dev/lguest. */
static int user_send_irq(struct lg_cpu *cpu, const unsigned long __user *input)
{
	unsigned long irq;

	if (get_user(irq, input) != 0)
		return -EFAULT;
	if (irq >= LGUEST_IRQS)
		return -EINVAL;
	/* Next time the Guest runs, the core code will see if it can deliver
	 * this interrupt. */
	set_bit(irq, cpu->irqs_pending);
	return 0;
}

/*L:040 Once our Guest is initialized, the Launcher makes it run by reading
 * from /dev/lguest. */
static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
{
	struct lguest *lg = file->private_data;
	struct lg_cpu *cpu;
	unsigned int cpu_id = *o;

	/* You must write LHREQ_INITIALIZE first! */
	if (!lg)
		return -EINVAL;

	/* Watch out for arbitrary vcpu indexes! */
	if (cpu_id >= lg->nr_cpus)
		return -EINVAL;

	cpu = &lg->cpus[cpu_id];

	/* If you're not the task which owns the Guest, go away. */
	if (current != cpu->tsk)
		return -EPERM;

	/* If the Guest is already dead, we indicate why */
	if (lg->dead) {
		size_t len;

		/* lg->dead either contains an error code, or a string. */
		if (IS_ERR(lg->dead))
			return PTR_ERR(lg->dead);

		/* We can only return as much as the buffer they read with. */
		len = min(size, strlen(lg->dead)+1);
		if (copy_to_user(user, lg->dead, len) != 0)
			return -EFAULT;
		return len;
	}

	/* If we returned from read() last time because the Guest sent I/O,
	 * clear the flag. */
	if (cpu->pending_notify)
		cpu->pending_notify = 0;

	/* Run the Guest until something interesting happens. */
	return run_guest(cpu, (unsigned long __user *)user);
}

/*L:025 This actually initializes a CPU.  For the moment, a Guest is only
 * uniprocessor, so "id" is always 0. */
static int lg_cpu_start(struct lg_cpu *cpu, unsigned id, unsigned long start_ip)
{
	/* We have a limited number the number of CPUs in the lguest struct. */
	if (id >= ARRAY_SIZE(cpu->lg->cpus))
		return -EINVAL;

	/* Set up this CPU's id, and pointer back to the lguest struct. */
	cpu->id = id;
	cpu->lg = container_of((cpu - id), struct lguest, cpus[0]);
	cpu->lg->nr_cpus++;

	/* Each CPU has a timer it can set. */
	init_clockdev(cpu);

	/* We need a complete page for the Guest registers: they are accessible
	 * to the Guest and we can only grant it access to whole pages. */
	cpu->regs_page = get_zeroed_page(GFP_KERNEL);
	if (!cpu->regs_page)
		return -ENOMEM;

	/* We actually put the registers at the bottom of the page. */
	cpu->regs = (void *)cpu->regs_page + PAGE_SIZE - sizeof(*cpu->regs);

	/* Now we initialize the Guest's registers, handing it the start
	 * address. */
	lguest_arch_setup_regs(cpu, start_ip);

	/* Initialize the queue for the Waker to wait on */
	init_waitqueue_head(&cpu->break_wq);

	/* We keep a pointer to the Launcher task (ie. current task) for when
	 * other Guests want to wake this one (eg. console input). */
	cpu->tsk = current;

	/* We need to keep a pointer to the Launcher's memory map, because if
	 * the Launcher dies we need to clean it up.  If we don't keep a
	 * reference, it is destroyed before close() is called. */
	cpu->mm = get_task_mm(cpu->tsk);

	/* We remember which CPU's pages this Guest used last, for optimization
	 * when the same Guest runs on the same CPU twice. */
	cpu->last_pages = NULL;

	/* No error == success. */
	return 0;
}

/*L:020 The initialization write supplies 3 pointer sized (32 or 64 bit)
 * values (in addition to the LHREQ_INITIALIZE value).  These are:
 *
 * base: The start of the Guest-physical memory inside the Launcher memory.
 *
 * pfnlimit: The highest (Guest-physical) page number the Guest should be
 * allowed to access.  The Guest memory lives inside the Launcher, so it sets
 * this to ensure the Guest can only reach its own memory.
 *
 * start: The first instruction to execute ("eip" in x86-speak).
 */
static int initialize(struct file *file, const unsigned long __user *input)
{
	/* "struct lguest" contains everything we (the Host) know about a
	 * Guest. */
	struct lguest *lg;
	int err;
	unsigned long args[3];

	/* We grab the Big Lguest lock, which protects against multiple
	 * simultaneous initializations. */
	mutex_lock(&lguest_lock);
	/* You can't initialize twice!  Close the device and start again... */
	if (file->private_data) {
		err = -EBUSY;
		goto unlock;
	}

	if (copy_from_user(args, input, sizeof(args)) != 0) {
		err = -EFAULT;
		goto unlock;
	}

	lg = kzalloc(sizeof(*lg), GFP_KERNEL);
	if (!lg) {
		err = -ENOMEM;
		goto unlock;
	}

	/* Populate the easy fields of our "struct lguest" */
	lg->mem_base = (void __user *)args[0];
	lg->pfn_limit = args[1];

	/* This is the first cpu (cpu 0) and it will start booting at args[2] */
	err = lg_cpu_start(&lg->cpus[0], 0, args[2]);
	if (err)
		goto release_guest;

	/* Initialize the Guest's shadow page tables, using the toplevel
	 * address the Launcher gave us.  This allocates memory, so can fail. */
	err = init_guest_pagetable(lg);
	if (err)
		goto free_regs;

	/* We keep our "struct lguest" in the file's private_data. */
	file->private_data = lg;

	mutex_unlock(&lguest_lock);

	/* And because this is a write() call, we return the length used. */
	return sizeof(args);

free_regs:
	/* FIXME: This should be in free_vcpu */
	free_page(lg->cpus[0].regs_page);
release_guest:
	kfree(lg);
unlock:
	mutex_unlock(&lguest_lock);
	return err;
}

/*L:010 The first operation the Launcher does must be a write.  All writes
 * start with an unsigned long number: for the first write this must be
 * LHREQ_INITIALIZE to set up the Guest.  After that the Launcher can use
 * writes of other values to send interrupts.
 *
 * Note that we overload the "offset" in the /dev/lguest file to indicate what
 * CPU number we're dealing with.  Currently this is always 0, since we only
 * support uniprocessor Guests, but you can see the beginnings of SMP support
 * here. */
static ssize_t write(struct file *file, const char __user *in,
		     size_t size, loff_t *off)
{
	/* Once the Guest is initialized, we hold the "struct lguest" in the
	 * file private data. */
	struct lguest *lg = file->private_data;
	const unsigned long __user *input = (const unsigned long __user *)in;
	unsigned long req;
	struct lg_cpu *uninitialized_var(cpu);
	unsigned int cpu_id = *off;

	/* The first value tells us what this request is. */
	if (get_user(req, input) != 0)
		return -EFAULT;
	input++;

	/* If you haven't initialized, you must do that first. */
	if (req != LHREQ_INITIALIZE) {
		if (!lg || (cpu_id >= lg->nr_cpus))
			return -EINVAL;
		cpu = &lg->cpus[cpu_id];

		/* Once the Guest is dead, you can only read() why it died. */
		if (lg->dead)
			return -ENOENT;

		/* If you're not the task which owns the Guest, all you can do
		 * is break the Launcher out of running the Guest. */
		if (current != cpu->tsk && req != LHREQ_BREAK)
			return -EPERM;
	}

	switch (req) {
	case LHREQ_INITIALIZE:
		return initialize(file, input);
	case LHREQ_IRQ:
		return user_send_irq(cpu, input);
	case LHREQ_BREAK:
		return break_guest_out(cpu, input);
	default:
		return -EINVAL;
	}
}

/*L:060 The final piece of interface code is the close() routine.  It reverses
 * everything done in initialize().  This is usually called because the
 * Launcher exited.
 *
 * Note that the close routine returns 0 or a negative error number: it can't
 * really fail, but it can whine.  I blame Sun for this wart, and K&R C for
 * letting them do it. :*/
static int close(struct inode *inode, struct file *file)
{
	struct lguest *lg = file->private_data;
	unsigned int i;

	/* If we never successfully initialized, there's nothing to clean up */
	if (!lg)
		return 0;

	/* We need the big lock, to protect from inter-guest I/O and other
	 * Launchers initializing guests. */
	mutex_lock(&lguest_lock);

	/* Free up the shadow page tables for the Guest. */
	free_guest_pagetable(lg);

	for (i = 0; i < lg->nr_cpus; i++) {
		/* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */
		hrtimer_cancel(&lg->cpus[i].hrt);
		/* We can free up the register page we allocated. */
		free_page(lg->cpus[i].regs_page);
		/* Now all the memory cleanups are done, it's safe to release
		 * the Launcher's memory management structure. */
		mmput(lg->cpus[i].mm);
	}
	/* If lg->dead doesn't contain an error code it will be NULL or a
	 * kmalloc()ed string, either of which is ok to hand to kfree(). */
	if (!IS_ERR(lg->dead))
		kfree(lg->dead);
	/* Free the memory allocated to the lguest_struct */
	kfree(lg);
	/* Release lock and exit. */
	mutex_unlock(&lguest_lock);

	return 0;
}

/*L:000
 * Welcome to our journey through the Launcher!
 *
 * The Launcher is the Host userspace program which sets up, runs and services
 * the Guest.  In fact, many comments in the Drivers which refer to "the Host"
 * doing things are inaccurate: the Launcher does all the device handling for
 * the Guest, but the Guest can't know that.
 *
 * Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we
 * shall see more of that later.
 *
 * We begin our understanding with the Host kernel interface which the Launcher
 * uses: reading and writing a character device called /dev/lguest.  All the
 * work happens in the read(), write() and close() routines: */
static struct file_operations lguest_fops = {
	.owner	 = THIS_MODULE,
	.release = close,
	.write	 = write,
	.read	 = read,
};

/* This is a textbook example of a "misc" character device.  Populate a "struct
 * miscdevice" and register it with misc_register(). */
static struct miscdevice lguest_dev = {
	.minor	= MISC_DYNAMIC_MINOR,
	.name	= "lguest",
	.fops	= &lguest_fops,
};

int __init lguest_device_init(void)
{
	return misc_register(&lguest_dev);
}

void __exit lguest_device_remove(void)
{
	misc_deregister(&lguest_dev);
}