lguest_user.c revision 133890103b9de08904f909995973e4b5c08a780e
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 <linux/eventfd.h> 11#include <linux/file.h> 12#include "lg.h" 13 14bool send_notify_to_eventfd(struct lg_cpu *cpu) 15{ 16 unsigned int i; 17 struct lg_eventfd_map *map; 18 19 /* lg->eventfds is RCU-protected */ 20 rcu_read_lock(); 21 map = rcu_dereference(cpu->lg->eventfds); 22 for (i = 0; i < map->num; i++) { 23 if (map->map[i].addr == cpu->pending_notify) { 24 eventfd_signal(map->map[i].event, 1); 25 cpu->pending_notify = 0; 26 break; 27 } 28 } 29 rcu_read_unlock(); 30 return cpu->pending_notify == 0; 31} 32 33static int add_eventfd(struct lguest *lg, unsigned long addr, int fd) 34{ 35 struct lg_eventfd_map *new, *old = lg->eventfds; 36 37 if (!addr) 38 return -EINVAL; 39 40 /* Replace the old array with the new one, carefully: others can 41 * be accessing it at the same time */ 42 new = kmalloc(sizeof(*new) + sizeof(new->map[0]) * (old->num + 1), 43 GFP_KERNEL); 44 if (!new) 45 return -ENOMEM; 46 47 /* First make identical copy. */ 48 memcpy(new->map, old->map, sizeof(old->map[0]) * old->num); 49 new->num = old->num; 50 51 /* Now append new entry. */ 52 new->map[new->num].addr = addr; 53 new->map[new->num].event = eventfd_ctx_fdget(fd); 54 if (IS_ERR(new->map[new->num].event)) { 55 kfree(new); 56 return PTR_ERR(new->map[new->num].event); 57 } 58 new->num++; 59 60 /* Now put new one in place. */ 61 rcu_assign_pointer(lg->eventfds, new); 62 63 /* We're not in a big hurry. Wait until noone's looking at old 64 * version, then delete it. */ 65 synchronize_rcu(); 66 kfree(old); 67 68 return 0; 69} 70 71static int attach_eventfd(struct lguest *lg, const unsigned long __user *input) 72{ 73 unsigned long addr, fd; 74 int err; 75 76 if (get_user(addr, input) != 0) 77 return -EFAULT; 78 input++; 79 if (get_user(fd, input) != 0) 80 return -EFAULT; 81 82 mutex_lock(&lguest_lock); 83 err = add_eventfd(lg, addr, fd); 84 mutex_unlock(&lguest_lock); 85 86 return 0; 87} 88 89/*L:050 Sending an interrupt is done by writing LHREQ_IRQ and an interrupt 90 * number to /dev/lguest. */ 91static int user_send_irq(struct lg_cpu *cpu, const unsigned long __user *input) 92{ 93 unsigned long irq; 94 95 if (get_user(irq, input) != 0) 96 return -EFAULT; 97 if (irq >= LGUEST_IRQS) 98 return -EINVAL; 99 100 set_interrupt(cpu, irq); 101 return 0; 102} 103 104/*L:040 Once our Guest is initialized, the Launcher makes it run by reading 105 * from /dev/lguest. */ 106static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o) 107{ 108 struct lguest *lg = file->private_data; 109 struct lg_cpu *cpu; 110 unsigned int cpu_id = *o; 111 112 /* You must write LHREQ_INITIALIZE first! */ 113 if (!lg) 114 return -EINVAL; 115 116 /* Watch out for arbitrary vcpu indexes! */ 117 if (cpu_id >= lg->nr_cpus) 118 return -EINVAL; 119 120 cpu = &lg->cpus[cpu_id]; 121 122 /* If you're not the task which owns the Guest, go away. */ 123 if (current != cpu->tsk) 124 return -EPERM; 125 126 /* If the Guest is already dead, we indicate why */ 127 if (lg->dead) { 128 size_t len; 129 130 /* lg->dead either contains an error code, or a string. */ 131 if (IS_ERR(lg->dead)) 132 return PTR_ERR(lg->dead); 133 134 /* We can only return as much as the buffer they read with. */ 135 len = min(size, strlen(lg->dead)+1); 136 if (copy_to_user(user, lg->dead, len) != 0) 137 return -EFAULT; 138 return len; 139 } 140 141 /* If we returned from read() last time because the Guest sent I/O, 142 * clear the flag. */ 143 if (cpu->pending_notify) 144 cpu->pending_notify = 0; 145 146 /* Run the Guest until something interesting happens. */ 147 return run_guest(cpu, (unsigned long __user *)user); 148} 149 150/*L:025 This actually initializes a CPU. For the moment, a Guest is only 151 * uniprocessor, so "id" is always 0. */ 152static int lg_cpu_start(struct lg_cpu *cpu, unsigned id, unsigned long start_ip) 153{ 154 /* We have a limited number the number of CPUs in the lguest struct. */ 155 if (id >= ARRAY_SIZE(cpu->lg->cpus)) 156 return -EINVAL; 157 158 /* Set up this CPU's id, and pointer back to the lguest struct. */ 159 cpu->id = id; 160 cpu->lg = container_of((cpu - id), struct lguest, cpus[0]); 161 cpu->lg->nr_cpus++; 162 163 /* Each CPU has a timer it can set. */ 164 init_clockdev(cpu); 165 166 /* We need a complete page for the Guest registers: they are accessible 167 * to the Guest and we can only grant it access to whole pages. */ 168 cpu->regs_page = get_zeroed_page(GFP_KERNEL); 169 if (!cpu->regs_page) 170 return -ENOMEM; 171 172 /* We actually put the registers at the bottom of the page. */ 173 cpu->regs = (void *)cpu->regs_page + PAGE_SIZE - sizeof(*cpu->regs); 174 175 /* Now we initialize the Guest's registers, handing it the start 176 * address. */ 177 lguest_arch_setup_regs(cpu, start_ip); 178 179 /* We keep a pointer to the Launcher task (ie. current task) for when 180 * other Guests want to wake this one (eg. console input). */ 181 cpu->tsk = current; 182 183 /* We need to keep a pointer to the Launcher's memory map, because if 184 * the Launcher dies we need to clean it up. If we don't keep a 185 * reference, it is destroyed before close() is called. */ 186 cpu->mm = get_task_mm(cpu->tsk); 187 188 /* We remember which CPU's pages this Guest used last, for optimization 189 * when the same Guest runs on the same CPU twice. */ 190 cpu->last_pages = NULL; 191 192 /* No error == success. */ 193 return 0; 194} 195 196/*L:020 The initialization write supplies 3 pointer sized (32 or 64 bit) 197 * values (in addition to the LHREQ_INITIALIZE value). These are: 198 * 199 * base: The start of the Guest-physical memory inside the Launcher memory. 200 * 201 * pfnlimit: The highest (Guest-physical) page number the Guest should be 202 * allowed to access. The Guest memory lives inside the Launcher, so it sets 203 * this to ensure the Guest can only reach its own memory. 204 * 205 * start: The first instruction to execute ("eip" in x86-speak). 206 */ 207static int initialize(struct file *file, const unsigned long __user *input) 208{ 209 /* "struct lguest" contains everything we (the Host) know about a 210 * Guest. */ 211 struct lguest *lg; 212 int err; 213 unsigned long args[3]; 214 215 /* We grab the Big Lguest lock, which protects against multiple 216 * simultaneous initializations. */ 217 mutex_lock(&lguest_lock); 218 /* You can't initialize twice! Close the device and start again... */ 219 if (file->private_data) { 220 err = -EBUSY; 221 goto unlock; 222 } 223 224 if (copy_from_user(args, input, sizeof(args)) != 0) { 225 err = -EFAULT; 226 goto unlock; 227 } 228 229 lg = kzalloc(sizeof(*lg), GFP_KERNEL); 230 if (!lg) { 231 err = -ENOMEM; 232 goto unlock; 233 } 234 235 lg->eventfds = kmalloc(sizeof(*lg->eventfds), GFP_KERNEL); 236 if (!lg->eventfds) { 237 err = -ENOMEM; 238 goto free_lg; 239 } 240 lg->eventfds->num = 0; 241 242 /* Populate the easy fields of our "struct lguest" */ 243 lg->mem_base = (void __user *)args[0]; 244 lg->pfn_limit = args[1]; 245 246 /* This is the first cpu (cpu 0) and it will start booting at args[2] */ 247 err = lg_cpu_start(&lg->cpus[0], 0, args[2]); 248 if (err) 249 goto free_eventfds; 250 251 /* Initialize the Guest's shadow page tables, using the toplevel 252 * address the Launcher gave us. This allocates memory, so can fail. */ 253 err = init_guest_pagetable(lg); 254 if (err) 255 goto free_regs; 256 257 /* We keep our "struct lguest" in the file's private_data. */ 258 file->private_data = lg; 259 260 mutex_unlock(&lguest_lock); 261 262 /* And because this is a write() call, we return the length used. */ 263 return sizeof(args); 264 265free_regs: 266 /* FIXME: This should be in free_vcpu */ 267 free_page(lg->cpus[0].regs_page); 268free_eventfds: 269 kfree(lg->eventfds); 270free_lg: 271 kfree(lg); 272unlock: 273 mutex_unlock(&lguest_lock); 274 return err; 275} 276 277/*L:010 The first operation the Launcher does must be a write. All writes 278 * start with an unsigned long number: for the first write this must be 279 * LHREQ_INITIALIZE to set up the Guest. After that the Launcher can use 280 * writes of other values to send interrupts. 281 * 282 * Note that we overload the "offset" in the /dev/lguest file to indicate what 283 * CPU number we're dealing with. Currently this is always 0, since we only 284 * support uniprocessor Guests, but you can see the beginnings of SMP support 285 * here. */ 286static ssize_t write(struct file *file, const char __user *in, 287 size_t size, loff_t *off) 288{ 289 /* Once the Guest is initialized, we hold the "struct lguest" in the 290 * file private data. */ 291 struct lguest *lg = file->private_data; 292 const unsigned long __user *input = (const unsigned long __user *)in; 293 unsigned long req; 294 struct lg_cpu *uninitialized_var(cpu); 295 unsigned int cpu_id = *off; 296 297 /* The first value tells us what this request is. */ 298 if (get_user(req, input) != 0) 299 return -EFAULT; 300 input++; 301 302 /* If you haven't initialized, you must do that first. */ 303 if (req != LHREQ_INITIALIZE) { 304 if (!lg || (cpu_id >= lg->nr_cpus)) 305 return -EINVAL; 306 cpu = &lg->cpus[cpu_id]; 307 308 /* Once the Guest is dead, you can only read() why it died. */ 309 if (lg->dead) 310 return -ENOENT; 311 } 312 313 switch (req) { 314 case LHREQ_INITIALIZE: 315 return initialize(file, input); 316 case LHREQ_IRQ: 317 return user_send_irq(cpu, input); 318 case LHREQ_EVENTFD: 319 return attach_eventfd(lg, input); 320 default: 321 return -EINVAL; 322 } 323} 324 325/*L:060 The final piece of interface code is the close() routine. It reverses 326 * everything done in initialize(). This is usually called because the 327 * Launcher exited. 328 * 329 * Note that the close routine returns 0 or a negative error number: it can't 330 * really fail, but it can whine. I blame Sun for this wart, and K&R C for 331 * letting them do it. :*/ 332static int close(struct inode *inode, struct file *file) 333{ 334 struct lguest *lg = file->private_data; 335 unsigned int i; 336 337 /* If we never successfully initialized, there's nothing to clean up */ 338 if (!lg) 339 return 0; 340 341 /* We need the big lock, to protect from inter-guest I/O and other 342 * Launchers initializing guests. */ 343 mutex_lock(&lguest_lock); 344 345 /* Free up the shadow page tables for the Guest. */ 346 free_guest_pagetable(lg); 347 348 for (i = 0; i < lg->nr_cpus; i++) { 349 /* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */ 350 hrtimer_cancel(&lg->cpus[i].hrt); 351 /* We can free up the register page we allocated. */ 352 free_page(lg->cpus[i].regs_page); 353 /* Now all the memory cleanups are done, it's safe to release 354 * the Launcher's memory management structure. */ 355 mmput(lg->cpus[i].mm); 356 } 357 358 /* Release any eventfds they registered. */ 359 for (i = 0; i < lg->eventfds->num; i++) 360 eventfd_ctx_put(lg->eventfds->map[i].event); 361 kfree(lg->eventfds); 362 363 /* If lg->dead doesn't contain an error code it will be NULL or a 364 * kmalloc()ed string, either of which is ok to hand to kfree(). */ 365 if (!IS_ERR(lg->dead)) 366 kfree(lg->dead); 367 /* Free the memory allocated to the lguest_struct */ 368 kfree(lg); 369 /* Release lock and exit. */ 370 mutex_unlock(&lguest_lock); 371 372 return 0; 373} 374 375/*L:000 376 * Welcome to our journey through the Launcher! 377 * 378 * The Launcher is the Host userspace program which sets up, runs and services 379 * the Guest. In fact, many comments in the Drivers which refer to "the Host" 380 * doing things are inaccurate: the Launcher does all the device handling for 381 * the Guest, but the Guest can't know that. 382 * 383 * Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we 384 * shall see more of that later. 385 * 386 * We begin our understanding with the Host kernel interface which the Launcher 387 * uses: reading and writing a character device called /dev/lguest. All the 388 * work happens in the read(), write() and close() routines: */ 389static struct file_operations lguest_fops = { 390 .owner = THIS_MODULE, 391 .release = close, 392 .write = write, 393 .read = read, 394}; 395 396/* This is a textbook example of a "misc" character device. Populate a "struct 397 * miscdevice" and register it with misc_register(). */ 398static struct miscdevice lguest_dev = { 399 .minor = MISC_DYNAMIC_MINOR, 400 .name = "lguest", 401 .fops = &lguest_fops, 402}; 403 404int __init lguest_device_init(void) 405{ 406 return misc_register(&lguest_dev); 407} 408 409void __exit lguest_device_remove(void) 410{ 411 misc_deregister(&lguest_dev); 412} 413