aboutsummaryrefslogtreecommitdiffstats
path: root/drivers/lguest/lguest_user.c
blob: 80d1b58c76986b9d245637e4e29999793260ddcd (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
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
/*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 memory size, pagetable, entry point and kernel address offset.
 * A read will run the Guest until a signal is pending (-EINTR), or the Guest
 * does a DMA out to the Launcher.  Writes are also used to get a DMA buffer
 * registered by the Guest and to send the Guest an interrupt. :*/
#include <linux/uaccess.h>
#include <linux/miscdevice.h>
#include <linux/fs.h>
#include "lg.h"

/*L:030 setup_regs() doesn't really belong in this file, but it gives us an
 * early glimpse deeper into the Host so it's worth having here.
 *
 * Most of the Guest's registers are left alone: we used get_zeroed_page() to
 * allocate the structure, so they will be 0. */
static void setup_regs(struct lguest_regs *regs, unsigned long start)
{
	/* There are four "segment" registers which the Guest needs to boot:
	 * The "code segment" register (cs) refers to the kernel code segment
	 * __KERNEL_CS, and the "data", "extra" and "stack" segment registers
	 * refer to the kernel data segment __KERNEL_DS.
	 *
	 * The privilege level is packed into the lower bits.  The Guest runs
	 * at privilege level 1 (GUEST_PL).*/
	regs->ds = regs->es = regs->ss = __KERNEL_DS|GUEST_PL;
	regs->cs = __KERNEL_CS|GUEST_PL;

	/* The "eflags" register contains miscellaneous flags.  Bit 1 (0x002)
	 * is supposed to always be "1".  Bit 9 (0x200) controls whether
	 * interrupts are enabled.  We always leave interrupts enabled while
	 * running the Guest. */
	regs->eflags = 0x202;

	/* The "Extended Instruction Pointer" register says where the Guest is
	 * running. */
	regs->eip = start;

	/* %esi points to our boot information, at physical address 0, so don't
	 * touch it. */
}

/*L:310 To send DMA into the Guest, the Launcher needs to be able to ask for a
 * DMA buffer.  This is done by writing LHREQ_GETDMA and the key to
 * /dev/lguest. */
static long user_get_dma(struct lguest *lg, const u32 __user *input)
{
	unsigned long key, udma, irq;

	/* Fetch the key they wrote to us. */
	if (get_user(key, input) != 0)
		return -EFAULT;
	/* Look for a free Guest DMA buffer bound to that key. */
	udma = get_dma_buffer(lg, key, &irq);
	if (!udma)
		return -ENOENT;

	/* We need to tell the Launcher what interrupt the Guest expects after
	 * the buffer is filled.  We stash it in udma->used_len. */
	lgwrite_u32(lg, udma + offsetof(struct lguest_dma, used_len), irq);

	/* The (guest-physical) address of the DMA buffer is returned from
	 * the write(). */
	return udma;
}

/*L:315 To force the Guest to stop running and return to the Launcher, the
 * Waker sets writes LHREQ_BREAK and the value "1" to /dev/lguest.  The
 * Launcher then writes LHREQ_BREAK and "0" to release the Waker. */
static int break_guest_out(struct lguest *lg, const u32 __user *input)
{
	unsigned long on;

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

	if (on) {
		lg->break_out = 1;
		/* Pop it out (may be running on different CPU) */
		wake_up_process(lg->tsk);
		/* Wait for them to reset it */
		return wait_event_interruptible(lg->break_wq, !lg->break_out);
	} else {
		lg->break_out = 0;
		wake_up(&lg->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 lguest *lg, const u32 __user *input)
{
	u32 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, lg->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;

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

	/* If you're not the task which owns the guest, go away. */
	if (current != lg->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 DMA,
	 * clear the flag. */
	if (lg->dma_is_pending)
		lg->dma_is_pending = 0;

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

/*L:020 The initialization write supplies 4 32-bit values (in addition to the
 * 32-bit LHREQ_INITIALIZE value).  These are:
 *
 * pfnlimit: The highest (Guest-physical) page number the Guest should be
 * allowed to access.  The Launcher has to live in Guest memory, so it sets
 * this to ensure the Guest can't reach it.
 *
 * pgdir: The (Guest-physical) address of the top of the initial Guest
 * pagetables (which are set up by the Launcher).
 *
 * start: The first instruction to execute ("eip" in x86-speak).
 *
 * page_offset: The PAGE_OFFSET constant in the Guest kernel.  We should
 * probably wean the code off this, but it's a very useful constant!  Any
 * address above this is within the Guest kernel, and any kernel address can
 * quickly converted from physical to virtual by adding PAGE_OFFSET.  It's
 * 0xC0000000 (3G) by default, but it's configurable at kernel build time.
 */
static int initialize(struct file *file, const u32 __user *input)
{
	/* "struct lguest" contains everything we (the Host) know about a
	 * Guest. */
	struct lguest *lg;
	int err, i;
	u32 args[4];

	/* We grab the Big Lguest lock, which protects the global array
	 * "lguests" and 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;
	}

	/* Find an unused guest. */
	i = find_free_guest();
	if (i < 0) {
		err = -ENOSPC;
		goto unlock;
	}
	/* OK, we have an index into the "lguest" array: "lg" is a convenient
	 * pointer. */
	lg = &lguests[i];

	/* Populate the easy fields of our "struct lguest" */
	lg->guestid = i;
	lg->pfn_limit = args[0];
	lg->page_offset = args[3];

	/* 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. */
	lg->regs_page = get_zeroed_page(GFP_KERNEL);
	if (!lg->regs_page) {
		err = -ENOMEM;
		goto release_guest;
	}
	/* We actually put the registers at the bottom of the page. */
	lg->regs = (void *)lg->regs_page + PAGE_SIZE - sizeof(*lg->regs);

	/* 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, args[1]);
	if (err)
		goto free_regs;

	/* Now we initialize the Guest's registers, handing it the start
	 * address. */
	setup_regs(lg->regs, args[2]);

	/* There are a couple of GDT entries the Guest expects when first
	 * booting. */
	setup_guest_gdt(lg);

	/* The timer for lguest's clock needs initialization. */
	init_clockdev(lg);

	/* We keep a pointer to the Launcher task (ie. current task) for when
	 * other Guests want to wake this one (inter-Guest I/O). */
	lg->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. */
	lg->mm = get_task_mm(lg->tsk);

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

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

	/* 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:
	free_page(lg->regs_page);
release_guest:
	memset(lg, 0, sizeof(*lg));
unlock:
	mutex_unlock(&lguest_lock);
	return err;
}

/*L:010 The first operation the Launcher does must be a write.  All writes
 * start with a 32 bit 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 get DMA buffers and send interrupts. */
static ssize_t write(struct file *file, const char __user *input,
		     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;
	u32 req;

	if (get_user(req, input) != 0)
		return -EFAULT;
	input += sizeof(req);

	/* If you haven't initialized, you must do that first. */
	if (req != LHREQ_INITIALIZE && !lg)
		return -EINVAL;

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

	/* If you're not the task which owns the Guest, you can only break */
	if (lg && current != lg->tsk && req != LHREQ_BREAK)
		return -EPERM;

	switch (req) {
	case LHREQ_INITIALIZE:
		return initialize(file, (const u32 __user *)input);
	case LHREQ_GETDMA:
		return user_get_dma(lg, (const u32 __user *)input);
	case LHREQ_IRQ:
		return user_send_irq(lg, (const u32 __user *)input);
	case LHREQ_BREAK:
		return break_guest_out(lg, (const u32 __user *)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;

	/* 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);
	/* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */
	hrtimer_cancel(&lg->hrt);
	/* Free any DMA buffers the Guest had bound. */
	release_all_dma(lg);
	/* Free up the shadow page tables for the Guest. */
	free_guest_pagetable(lg);
	/* Now all the memory cleanups are done, it's safe to release the
	 * Launcher's memory management structure. */
	mmput(lg->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);
	/* We can free up the register page we allocated. */
	free_page(lg->regs_page);
	/* We clear the entire structure, which also marks it as free for the
	 * next user. */
	memset(lg, 0, sizeof(*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.  The Guest can't tell what's done by the the Launcher and what by
 * the Host.
 *
 * 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);
}