lguest_user.c revision 43054412db5e5b3eda1eff6c2245ff4257560340
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 "lg.h" 10 11/*L:055 When something happens, the Waker process needs a way to stop the 12 * kernel running the Guest and return to the Launcher. So the Waker writes 13 * LHREQ_BREAK and the value "1" to /dev/lguest to do this. Once the Launcher 14 * has done whatever needs attention, it writes LHREQ_BREAK and "0" to release 15 * the Waker. */ 16static int break_guest_out(struct lguest *lg, const unsigned long __user *input) 17{ 18 unsigned long on; 19 20 /* Fetch whether they're turning break on or off. */ 21 if (get_user(on, input) != 0) 22 return -EFAULT; 23 24 if (on) { 25 lg->break_out = 1; 26 /* Pop it out of the Guest (may be running on different CPU) */ 27 wake_up_process(lg->tsk); 28 /* Wait for them to reset it */ 29 return wait_event_interruptible(lg->break_wq, !lg->break_out); 30 } else { 31 lg->break_out = 0; 32 wake_up(&lg->break_wq); 33 return 0; 34 } 35} 36 37/*L:050 Sending an interrupt is done by writing LHREQ_IRQ and an interrupt 38 * number to /dev/lguest. */ 39static int user_send_irq(struct lguest *lg, const unsigned long __user *input) 40{ 41 unsigned long irq; 42 43 if (get_user(irq, input) != 0) 44 return -EFAULT; 45 if (irq >= LGUEST_IRQS) 46 return -EINVAL; 47 /* Next time the Guest runs, the core code will see if it can deliver 48 * this interrupt. */ 49 set_bit(irq, lg->irqs_pending); 50 return 0; 51} 52 53/*L:040 Once our Guest is initialized, the Launcher makes it run by reading 54 * from /dev/lguest. */ 55static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o) 56{ 57 struct lguest *lg = file->private_data; 58 59 /* You must write LHREQ_INITIALIZE first! */ 60 if (!lg) 61 return -EINVAL; 62 63 /* If you're not the task which owns the Guest, go away. */ 64 if (current != lg->tsk) 65 return -EPERM; 66 67 /* If the guest is already dead, we indicate why */ 68 if (lg->dead) { 69 size_t len; 70 71 /* lg->dead either contains an error code, or a string. */ 72 if (IS_ERR(lg->dead)) 73 return PTR_ERR(lg->dead); 74 75 /* We can only return as much as the buffer they read with. */ 76 len = min(size, strlen(lg->dead)+1); 77 if (copy_to_user(user, lg->dead, len) != 0) 78 return -EFAULT; 79 return len; 80 } 81 82 /* If we returned from read() last time because the Guest notified, 83 * clear the flag. */ 84 if (lg->pending_notify) 85 lg->pending_notify = 0; 86 87 /* Run the Guest until something interesting happens. */ 88 return run_guest(lg, (unsigned long __user *)user); 89} 90 91/*L:020 The initialization write supplies 4 pointer sized (32 or 64 bit) 92 * values (in addition to the LHREQ_INITIALIZE value). These are: 93 * 94 * base: The start of the Guest-physical memory inside the Launcher memory. 95 * 96 * pfnlimit: The highest (Guest-physical) page number the Guest should be 97 * allowed to access. The Guest memory lives inside the Launcher, so it sets 98 * this to ensure the Guest can only reach its own memory. 99 * 100 * pgdir: The (Guest-physical) address of the top of the initial Guest 101 * pagetables (which are set up by the Launcher). 102 * 103 * start: The first instruction to execute ("eip" in x86-speak). 104 */ 105static int initialize(struct file *file, const unsigned long __user *input) 106{ 107 /* "struct lguest" contains everything we (the Host) know about a 108 * Guest. */ 109 struct lguest *lg; 110 int err; 111 unsigned long args[4]; 112 113 /* We grab the Big Lguest lock, which protects against multiple 114 * simultaneous initializations. */ 115 mutex_lock(&lguest_lock); 116 /* You can't initialize twice! Close the device and start again... */ 117 if (file->private_data) { 118 err = -EBUSY; 119 goto unlock; 120 } 121 122 if (copy_from_user(args, input, sizeof(args)) != 0) { 123 err = -EFAULT; 124 goto unlock; 125 } 126 127 lg = kzalloc(sizeof(*lg), GFP_KERNEL); 128 if (!lg) { 129 err = -ENOMEM; 130 goto unlock; 131 } 132 133 /* Populate the easy fields of our "struct lguest" */ 134 lg->mem_base = (void __user *)(long)args[0]; 135 lg->pfn_limit = args[1]; 136 137 /* We need a complete page for the Guest registers: they are accessible 138 * to the Guest and we can only grant it access to whole pages. */ 139 lg->regs_page = get_zeroed_page(GFP_KERNEL); 140 if (!lg->regs_page) { 141 err = -ENOMEM; 142 goto release_guest; 143 } 144 /* We actually put the registers at the bottom of the page. */ 145 lg->regs = (void *)lg->regs_page + PAGE_SIZE - sizeof(*lg->regs); 146 147 /* Initialize the Guest's shadow page tables, using the toplevel 148 * address the Launcher gave us. This allocates memory, so can 149 * fail. */ 150 err = init_guest_pagetable(lg, args[2]); 151 if (err) 152 goto free_regs; 153 154 /* Now we initialize the Guest's registers, handing it the start 155 * address. */ 156 lguest_arch_setup_regs(lg, args[3]); 157 158 /* The timer for lguest's clock needs initialization. */ 159 init_clockdev(lg); 160 161 /* We keep a pointer to the Launcher task (ie. current task) for when 162 * other Guests want to wake this one (inter-Guest I/O). */ 163 lg->tsk = current; 164 /* We need to keep a pointer to the Launcher's memory map, because if 165 * the Launcher dies we need to clean it up. If we don't keep a 166 * reference, it is destroyed before close() is called. */ 167 lg->mm = get_task_mm(lg->tsk); 168 169 /* Initialize the queue for the waker to wait on */ 170 init_waitqueue_head(&lg->break_wq); 171 172 /* We remember which CPU's pages this Guest used last, for optimization 173 * when the same Guest runs on the same CPU twice. */ 174 lg->last_pages = NULL; 175 176 /* We keep our "struct lguest" in the file's private_data. */ 177 file->private_data = lg; 178 179 mutex_unlock(&lguest_lock); 180 181 /* And because this is a write() call, we return the length used. */ 182 return sizeof(args); 183 184free_regs: 185 free_page(lg->regs_page); 186release_guest: 187 kfree(lg); 188unlock: 189 mutex_unlock(&lguest_lock); 190 return err; 191} 192 193/*L:010 The first operation the Launcher does must be a write. All writes 194 * start with an unsigned long number: for the first write this must be 195 * LHREQ_INITIALIZE to set up the Guest. After that the Launcher can use 196 * writes of other values to send interrupts. */ 197static ssize_t write(struct file *file, const char __user *in, 198 size_t size, loff_t *off) 199{ 200 /* Once the guest is initialized, we hold the "struct lguest" in the 201 * file private data. */ 202 struct lguest *lg = file->private_data; 203 const unsigned long __user *input = (const unsigned long __user *)in; 204 unsigned long req; 205 206 if (get_user(req, input) != 0) 207 return -EFAULT; 208 input++; 209 210 /* If you haven't initialized, you must do that first. */ 211 if (req != LHREQ_INITIALIZE && !lg) 212 return -EINVAL; 213 214 /* Once the Guest is dead, all you can do is read() why it died. */ 215 if (lg && lg->dead) 216 return -ENOENT; 217 218 /* If you're not the task which owns the Guest, you can only break */ 219 if (lg && current != lg->tsk && req != LHREQ_BREAK) 220 return -EPERM; 221 222 switch (req) { 223 case LHREQ_INITIALIZE: 224 return initialize(file, input); 225 case LHREQ_IRQ: 226 return user_send_irq(lg, input); 227 case LHREQ_BREAK: 228 return break_guest_out(lg, input); 229 default: 230 return -EINVAL; 231 } 232} 233 234/*L:060 The final piece of interface code is the close() routine. It reverses 235 * everything done in initialize(). This is usually called because the 236 * Launcher exited. 237 * 238 * Note that the close routine returns 0 or a negative error number: it can't 239 * really fail, but it can whine. I blame Sun for this wart, and K&R C for 240 * letting them do it. :*/ 241static int close(struct inode *inode, struct file *file) 242{ 243 struct lguest *lg = file->private_data; 244 245 /* If we never successfully initialized, there's nothing to clean up */ 246 if (!lg) 247 return 0; 248 249 /* We need the big lock, to protect from inter-guest I/O and other 250 * Launchers initializing guests. */ 251 mutex_lock(&lguest_lock); 252 /* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */ 253 hrtimer_cancel(&lg->hrt); 254 /* Free up the shadow page tables for the Guest. */ 255 free_guest_pagetable(lg); 256 /* Now all the memory cleanups are done, it's safe to release the 257 * Launcher's memory management structure. */ 258 mmput(lg->mm); 259 /* If lg->dead doesn't contain an error code it will be NULL or a 260 * kmalloc()ed string, either of which is ok to hand to kfree(). */ 261 if (!IS_ERR(lg->dead)) 262 kfree(lg->dead); 263 /* We can free up the register page we allocated. */ 264 free_page(lg->regs_page); 265 /* We clear the entire structure, which also marks it as free for the 266 * next user. */ 267 memset(lg, 0, sizeof(*lg)); 268 /* Release lock and exit. */ 269 mutex_unlock(&lguest_lock); 270 271 return 0; 272} 273 274/*L:000 275 * Welcome to our journey through the Launcher! 276 * 277 * The Launcher is the Host userspace program which sets up, runs and services 278 * the Guest. In fact, many comments in the Drivers which refer to "the Host" 279 * doing things are inaccurate: the Launcher does all the device handling for 280 * the Guest, but the Guest can't know that. 281 * 282 * Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we 283 * shall see more of that later. 284 * 285 * We begin our understanding with the Host kernel interface which the Launcher 286 * uses: reading and writing a character device called /dev/lguest. All the 287 * work happens in the read(), write() and close() routines: */ 288static struct file_operations lguest_fops = { 289 .owner = THIS_MODULE, 290 .release = close, 291 .write = write, 292 .read = read, 293}; 294 295/* This is a textbook example of a "misc" character device. Populate a "struct 296 * miscdevice" and register it with misc_register(). */ 297static struct miscdevice lguest_dev = { 298 .minor = MISC_DYNAMIC_MINOR, 299 .name = "lguest", 300 .fops = &lguest_fops, 301}; 302 303int __init lguest_device_init(void) 304{ 305 return misc_register(&lguest_dev); 306} 307 308void __exit lguest_device_remove(void) 309{ 310 misc_deregister(&lguest_dev); 311} 312