1 /*P:200 This contains all the /dev/lguest code, whereby the userspace launcher
2 * controls and communicates with the Guest. For example, the first write will
3 * tell us the Guest's memory layout, pagetable, entry point and kernel address
4 * offset. A read will run the Guest until something happens, such as a signal
5 * or the Guest doing a NOTIFY out to the Launcher. :*/
6 #include <linux/uaccess.h>
7 #include <linux/miscdevice.h>
8 #include <linux/fs.h>
9 #include <linux/sched.h>
10 #include "lg.h"
11
12 /*L:055 When something happens, the Waker process needs a way to stop the
13 * kernel running the Guest and return to the Launcher. So the Waker writes
14 * LHREQ_BREAK and the value "1" to /dev/lguest to do this. Once the Launcher
15 * has done whatever needs attention, it writes LHREQ_BREAK and "0" to release
16 * the Waker. */
break_guest_out(struct lg_cpu * cpu,const unsigned long __user * input)17 static int break_guest_out(struct lg_cpu *cpu, const unsigned long __user*input)
18 {
19 unsigned long on;
20
21 /* Fetch whether they're turning break on or off. */
22 if (get_user(on, input) != 0)
23 return -EFAULT;
24
25 if (on) {
26 cpu->break_out = 1;
27 /* Pop it out of the Guest (may be running on different CPU) */
28 wake_up_process(cpu->tsk);
29 /* Wait for them to reset it */
30 return wait_event_interruptible(cpu->break_wq, !cpu->break_out);
31 } else {
32 cpu->break_out = 0;
33 wake_up(&cpu->break_wq);
34 return 0;
35 }
36 }
37
38 /*L:050 Sending an interrupt is done by writing LHREQ_IRQ and an interrupt
39 * number to /dev/lguest. */
user_send_irq(struct lg_cpu * cpu,const unsigned long __user * input)40 static int user_send_irq(struct lg_cpu *cpu, const unsigned long __user *input)
41 {
42 unsigned long irq;
43
44 if (get_user(irq, input) != 0)
45 return -EFAULT;
46 if (irq >= LGUEST_IRQS)
47 return -EINVAL;
48 /* Next time the Guest runs, the core code will see if it can deliver
49 * this interrupt. */
50 set_bit(irq, cpu->irqs_pending);
51 return 0;
52 }
53
54 /*L:040 Once our Guest is initialized, the Launcher makes it run by reading
55 * from /dev/lguest. */
read(struct file * file,char __user * user,size_t size,loff_t * o)56 static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
57 {
58 struct lguest *lg = file->private_data;
59 struct lg_cpu *cpu;
60 unsigned int cpu_id = *o;
61
62 /* You must write LHREQ_INITIALIZE first! */
63 if (!lg)
64 return -EINVAL;
65
66 /* Watch out for arbitrary vcpu indexes! */
67 if (cpu_id >= lg->nr_cpus)
68 return -EINVAL;
69
70 cpu = &lg->cpus[cpu_id];
71
72 /* If you're not the task which owns the Guest, go away. */
73 if (current != cpu->tsk)
74 return -EPERM;
75
76 /* If the Guest is already dead, we indicate why */
77 if (lg->dead) {
78 size_t len;
79
80 /* lg->dead either contains an error code, or a string. */
81 if (IS_ERR(lg->dead))
82 return PTR_ERR(lg->dead);
83
84 /* We can only return as much as the buffer they read with. */
85 len = min(size, strlen(lg->dead)+1);
86 if (copy_to_user(user, lg->dead, len) != 0)
87 return -EFAULT;
88 return len;
89 }
90
91 /* If we returned from read() last time because the Guest sent I/O,
92 * clear the flag. */
93 if (cpu->pending_notify)
94 cpu->pending_notify = 0;
95
96 /* Run the Guest until something interesting happens. */
97 return run_guest(cpu, (unsigned long __user *)user);
98 }
99
100 /*L:025 This actually initializes a CPU. For the moment, a Guest is only
101 * uniprocessor, so "id" is always 0. */
lg_cpu_start(struct lg_cpu * cpu,unsigned id,unsigned long start_ip)102 static int lg_cpu_start(struct lg_cpu *cpu, unsigned id, unsigned long start_ip)
103 {
104 /* We have a limited number the number of CPUs in the lguest struct. */
105 if (id >= ARRAY_SIZE(cpu->lg->cpus))
106 return -EINVAL;
107
108 /* Set up this CPU's id, and pointer back to the lguest struct. */
109 cpu->id = id;
110 cpu->lg = container_of((cpu - id), struct lguest, cpus[0]);
111 cpu->lg->nr_cpus++;
112
113 /* Each CPU has a timer it can set. */
114 init_clockdev(cpu);
115
116 /* We need a complete page for the Guest registers: they are accessible
117 * to the Guest and we can only grant it access to whole pages. */
118 cpu->regs_page = get_zeroed_page(GFP_KERNEL);
119 if (!cpu->regs_page)
120 return -ENOMEM;
121
122 /* We actually put the registers at the bottom of the page. */
123 cpu->regs = (void *)cpu->regs_page + PAGE_SIZE - sizeof(*cpu->regs);
124
125 /* Now we initialize the Guest's registers, handing it the start
126 * address. */
127 lguest_arch_setup_regs(cpu, start_ip);
128
129 /* Initialize the queue for the Waker to wait on */
130 init_waitqueue_head(&cpu->break_wq);
131
132 /* We keep a pointer to the Launcher task (ie. current task) for when
133 * other Guests want to wake this one (eg. console input). */
134 cpu->tsk = current;
135
136 /* We need to keep a pointer to the Launcher's memory map, because if
137 * the Launcher dies we need to clean it up. If we don't keep a
138 * reference, it is destroyed before close() is called. */
139 cpu->mm = get_task_mm(cpu->tsk);
140
141 /* We remember which CPU's pages this Guest used last, for optimization
142 * when the same Guest runs on the same CPU twice. */
143 cpu->last_pages = NULL;
144
145 /* No error == success. */
146 return 0;
147 }
148
149 /*L:020 The initialization write supplies 3 pointer sized (32 or 64 bit)
150 * values (in addition to the LHREQ_INITIALIZE value). These are:
151 *
152 * base: The start of the Guest-physical memory inside the Launcher memory.
153 *
154 * pfnlimit: The highest (Guest-physical) page number the Guest should be
155 * allowed to access. The Guest memory lives inside the Launcher, so it sets
156 * this to ensure the Guest can only reach its own memory.
157 *
158 * start: The first instruction to execute ("eip" in x86-speak).
159 */
initialize(struct file * file,const unsigned long __user * input)160 static int initialize(struct file *file, const unsigned long __user *input)
161 {
162 /* "struct lguest" contains everything we (the Host) know about a
163 * Guest. */
164 struct lguest *lg;
165 int err;
166 unsigned long args[3];
167
168 /* We grab the Big Lguest lock, which protects against multiple
169 * simultaneous initializations. */
170 mutex_lock(&lguest_lock);
171 /* You can't initialize twice! Close the device and start again... */
172 if (file->private_data) {
173 err = -EBUSY;
174 goto unlock;
175 }
176
177 if (copy_from_user(args, input, sizeof(args)) != 0) {
178 err = -EFAULT;
179 goto unlock;
180 }
181
182 lg = kzalloc(sizeof(*lg), GFP_KERNEL);
183 if (!lg) {
184 err = -ENOMEM;
185 goto unlock;
186 }
187
188 /* Populate the easy fields of our "struct lguest" */
189 lg->mem_base = (void __user *)args[0];
190 lg->pfn_limit = args[1];
191
192 /* This is the first cpu (cpu 0) and it will start booting at args[2] */
193 err = lg_cpu_start(&lg->cpus[0], 0, args[2]);
194 if (err)
195 goto release_guest;
196
197 /* Initialize the Guest's shadow page tables, using the toplevel
198 * address the Launcher gave us. This allocates memory, so can fail. */
199 err = init_guest_pagetable(lg);
200 if (err)
201 goto free_regs;
202
203 /* We keep our "struct lguest" in the file's private_data. */
204 file->private_data = lg;
205
206 mutex_unlock(&lguest_lock);
207
208 /* And because this is a write() call, we return the length used. */
209 return sizeof(args);
210
211 free_regs:
212 /* FIXME: This should be in free_vcpu */
213 free_page(lg->cpus[0].regs_page);
214 release_guest:
215 kfree(lg);
216 unlock:
217 mutex_unlock(&lguest_lock);
218 return err;
219 }
220
221 /*L:010 The first operation the Launcher does must be a write. All writes
222 * start with an unsigned long number: for the first write this must be
223 * LHREQ_INITIALIZE to set up the Guest. After that the Launcher can use
224 * writes of other values to send interrupts.
225 *
226 * Note that we overload the "offset" in the /dev/lguest file to indicate what
227 * CPU number we're dealing with. Currently this is always 0, since we only
228 * support uniprocessor Guests, but you can see the beginnings of SMP support
229 * here. */
write(struct file * file,const char __user * in,size_t size,loff_t * off)230 static ssize_t write(struct file *file, const char __user *in,
231 size_t size, loff_t *off)
232 {
233 /* Once the Guest is initialized, we hold the "struct lguest" in the
234 * file private data. */
235 struct lguest *lg = file->private_data;
236 const unsigned long __user *input = (const unsigned long __user *)in;
237 unsigned long req;
238 struct lg_cpu *uninitialized_var(cpu);
239 unsigned int cpu_id = *off;
240
241 /* The first value tells us what this request is. */
242 if (get_user(req, input) != 0)
243 return -EFAULT;
244 input++;
245
246 /* If you haven't initialized, you must do that first. */
247 if (req != LHREQ_INITIALIZE) {
248 if (!lg || (cpu_id >= lg->nr_cpus))
249 return -EINVAL;
250 cpu = &lg->cpus[cpu_id];
251
252 /* Once the Guest is dead, you can only read() why it died. */
253 if (lg->dead)
254 return -ENOENT;
255
256 /* If you're not the task which owns the Guest, all you can do
257 * is break the Launcher out of running the Guest. */
258 if (current != cpu->tsk && req != LHREQ_BREAK)
259 return -EPERM;
260 }
261
262 switch (req) {
263 case LHREQ_INITIALIZE:
264 return initialize(file, input);
265 case LHREQ_IRQ:
266 return user_send_irq(cpu, input);
267 case LHREQ_BREAK:
268 return break_guest_out(cpu, input);
269 default:
270 return -EINVAL;
271 }
272 }
273
274 /*L:060 The final piece of interface code is the close() routine. It reverses
275 * everything done in initialize(). This is usually called because the
276 * Launcher exited.
277 *
278 * Note that the close routine returns 0 or a negative error number: it can't
279 * really fail, but it can whine. I blame Sun for this wart, and K&R C for
280 * letting them do it. :*/
close(struct inode * inode,struct file * file)281 static int close(struct inode *inode, struct file *file)
282 {
283 struct lguest *lg = file->private_data;
284 unsigned int i;
285
286 /* If we never successfully initialized, there's nothing to clean up */
287 if (!lg)
288 return 0;
289
290 /* We need the big lock, to protect from inter-guest I/O and other
291 * Launchers initializing guests. */
292 mutex_lock(&lguest_lock);
293
294 /* Free up the shadow page tables for the Guest. */
295 free_guest_pagetable(lg);
296
297 for (i = 0; i < lg->nr_cpus; i++) {
298 /* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */
299 hrtimer_cancel(&lg->cpus[i].hrt);
300 /* We can free up the register page we allocated. */
301 free_page(lg->cpus[i].regs_page);
302 /* Now all the memory cleanups are done, it's safe to release
303 * the Launcher's memory management structure. */
304 mmput(lg->cpus[i].mm);
305 }
306 /* If lg->dead doesn't contain an error code it will be NULL or a
307 * kmalloc()ed string, either of which is ok to hand to kfree(). */
308 if (!IS_ERR(lg->dead))
309 kfree(lg->dead);
310 /* Free the memory allocated to the lguest_struct */
311 kfree(lg);
312 /* Release lock and exit. */
313 mutex_unlock(&lguest_lock);
314
315 return 0;
316 }
317
318 /*L:000
319 * Welcome to our journey through the Launcher!
320 *
321 * The Launcher is the Host userspace program which sets up, runs and services
322 * the Guest. In fact, many comments in the Drivers which refer to "the Host"
323 * doing things are inaccurate: the Launcher does all the device handling for
324 * the Guest, but the Guest can't know that.
325 *
326 * Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we
327 * shall see more of that later.
328 *
329 * We begin our understanding with the Host kernel interface which the Launcher
330 * uses: reading and writing a character device called /dev/lguest. All the
331 * work happens in the read(), write() and close() routines: */
332 static struct file_operations lguest_fops = {
333 .owner = THIS_MODULE,
334 .release = close,
335 .write = write,
336 .read = read,
337 };
338
339 /* This is a textbook example of a "misc" character device. Populate a "struct
340 * miscdevice" and register it with misc_register(). */
341 static struct miscdevice lguest_dev = {
342 .minor = MISC_DYNAMIC_MINOR,
343 .name = "lguest",
344 .fops = &lguest_fops,
345 };
346
lguest_device_init(void)347 int __init lguest_device_init(void)
348 {
349 return misc_register(&lguest_dev);
350 }
351
lguest_device_remove(void)352 void __exit lguest_device_remove(void)
353 {
354 misc_deregister(&lguest_dev);
355 }
356