lguest_user.c revision 3c6b5bfa3cf3b4057788e08482a468cc3bc00780
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 DMA out to the Launcher. Writes are also used to get a 6 * DMA buffer registered by the Guest and to send the Guest an interrupt. :*/ 7#include <linux/uaccess.h> 8#include <linux/miscdevice.h> 9#include <linux/fs.h> 10#include "lg.h" 11 12/*L:030 setup_regs() doesn't really belong in this file, but it gives us an 13 * early glimpse deeper into the Host so it's worth having here. 14 * 15 * Most of the Guest's registers are left alone: we used get_zeroed_page() to 16 * allocate the structure, so they will be 0. */ 17static void setup_regs(struct lguest_regs *regs, unsigned long start) 18{ 19 /* There are four "segment" registers which the Guest needs to boot: 20 * The "code segment" register (cs) refers to the kernel code segment 21 * __KERNEL_CS, and the "data", "extra" and "stack" segment registers 22 * refer to the kernel data segment __KERNEL_DS. 23 * 24 * The privilege level is packed into the lower bits. The Guest runs 25 * at privilege level 1 (GUEST_PL).*/ 26 regs->ds = regs->es = regs->ss = __KERNEL_DS|GUEST_PL; 27 regs->cs = __KERNEL_CS|GUEST_PL; 28 29 /* The "eflags" register contains miscellaneous flags. Bit 1 (0x002) 30 * is supposed to always be "1". Bit 9 (0x200) controls whether 31 * interrupts are enabled. We always leave interrupts enabled while 32 * running the Guest. */ 33 regs->eflags = 0x202; 34 35 /* The "Extended Instruction Pointer" register says where the Guest is 36 * running. */ 37 regs->eip = start; 38 39 /* %esi points to our boot information, at physical address 0, so don't 40 * touch it. */ 41} 42 43/*L:310 To send DMA into the Guest, the Launcher needs to be able to ask for a 44 * DMA buffer. This is done by writing LHREQ_GETDMA and the key to 45 * /dev/lguest. */ 46static long user_get_dma(struct lguest *lg, const u32 __user *input) 47{ 48 unsigned long key, udma, irq; 49 50 /* Fetch the key they wrote to us. */ 51 if (get_user(key, input) != 0) 52 return -EFAULT; 53 /* Look for a free Guest DMA buffer bound to that key. */ 54 udma = get_dma_buffer(lg, key, &irq); 55 if (!udma) 56 return -ENOENT; 57 58 /* We need to tell the Launcher what interrupt the Guest expects after 59 * the buffer is filled. We stash it in udma->used_len. */ 60 lgwrite_u32(lg, udma + offsetof(struct lguest_dma, used_len), irq); 61 62 /* The (guest-physical) address of the DMA buffer is returned from 63 * the write(). */ 64 return udma; 65} 66 67/*L:315 To force the Guest to stop running and return to the Launcher, the 68 * Waker sets writes LHREQ_BREAK and the value "1" to /dev/lguest. The 69 * Launcher then writes LHREQ_BREAK and "0" to release the Waker. */ 70static int break_guest_out(struct lguest *lg, const u32 __user *input) 71{ 72 unsigned long on; 73 74 /* Fetch whether they're turning break on or off.. */ 75 if (get_user(on, input) != 0) 76 return -EFAULT; 77 78 if (on) { 79 lg->break_out = 1; 80 /* Pop it out (may be running on different CPU) */ 81 wake_up_process(lg->tsk); 82 /* Wait for them to reset it */ 83 return wait_event_interruptible(lg->break_wq, !lg->break_out); 84 } else { 85 lg->break_out = 0; 86 wake_up(&lg->break_wq); 87 return 0; 88 } 89} 90 91/*L:050 Sending an interrupt is done by writing LHREQ_IRQ and an interrupt 92 * number to /dev/lguest. */ 93static int user_send_irq(struct lguest *lg, const u32 __user *input) 94{ 95 u32 irq; 96 97 if (get_user(irq, input) != 0) 98 return -EFAULT; 99 if (irq >= LGUEST_IRQS) 100 return -EINVAL; 101 /* Next time the Guest runs, the core code will see if it can deliver 102 * this interrupt. */ 103 set_bit(irq, lg->irqs_pending); 104 return 0; 105} 106 107/*L:040 Once our Guest is initialized, the Launcher makes it run by reading 108 * from /dev/lguest. */ 109static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o) 110{ 111 struct lguest *lg = file->private_data; 112 113 /* You must write LHREQ_INITIALIZE first! */ 114 if (!lg) 115 return -EINVAL; 116 117 /* If you're not the task which owns the guest, go away. */ 118 if (current != lg->tsk) 119 return -EPERM; 120 121 /* If the guest is already dead, we indicate why */ 122 if (lg->dead) { 123 size_t len; 124 125 /* lg->dead either contains an error code, or a string. */ 126 if (IS_ERR(lg->dead)) 127 return PTR_ERR(lg->dead); 128 129 /* We can only return as much as the buffer they read with. */ 130 len = min(size, strlen(lg->dead)+1); 131 if (copy_to_user(user, lg->dead, len) != 0) 132 return -EFAULT; 133 return len; 134 } 135 136 /* If we returned from read() last time because the Guest sent DMA, 137 * clear the flag. */ 138 if (lg->dma_is_pending) 139 lg->dma_is_pending = 0; 140 141 /* Run the Guest until something interesting happens. */ 142 return run_guest(lg, (unsigned long __user *)user); 143} 144 145/*L:020 The initialization write supplies 5 32-bit values (in addition to the 146 * 32-bit LHREQ_INITIALIZE value). These are: 147 * 148 * base: The start of the Guest-physical memory inside the Launcher memory. 149 * 150 * pfnlimit: The highest (Guest-physical) page number the Guest should be 151 * allowed to access. The Launcher has to live in Guest memory, so it sets 152 * this to ensure the Guest can't reach it. 153 * 154 * pgdir: The (Guest-physical) address of the top of the initial Guest 155 * pagetables (which are set up by the Launcher). 156 * 157 * start: The first instruction to execute ("eip" in x86-speak). 158 * 159 * page_offset: The PAGE_OFFSET constant in the Guest kernel. We should 160 * probably wean the code off this, but it's a very useful constant! Any 161 * address above this is within the Guest kernel, and any kernel address can 162 * quickly converted from physical to virtual by adding PAGE_OFFSET. It's 163 * 0xC0000000 (3G) by default, but it's configurable at kernel build time. 164 */ 165static int initialize(struct file *file, const u32 __user *input) 166{ 167 /* "struct lguest" contains everything we (the Host) know about a 168 * Guest. */ 169 struct lguest *lg; 170 int err, i; 171 u32 args[5]; 172 173 /* We grab the Big Lguest lock, which protects the global array 174 * "lguests" and multiple simultaneous initializations. */ 175 mutex_lock(&lguest_lock); 176 /* You can't initialize twice! Close the device and start again... */ 177 if (file->private_data) { 178 err = -EBUSY; 179 goto unlock; 180 } 181 182 if (copy_from_user(args, input, sizeof(args)) != 0) { 183 err = -EFAULT; 184 goto unlock; 185 } 186 187 /* Find an unused guest. */ 188 i = find_free_guest(); 189 if (i < 0) { 190 err = -ENOSPC; 191 goto unlock; 192 } 193 /* OK, we have an index into the "lguest" array: "lg" is a convenient 194 * pointer. */ 195 lg = &lguests[i]; 196 197 /* Populate the easy fields of our "struct lguest" */ 198 lg->guestid = i; 199 lg->mem_base = (void __user *)(long)args[0]; 200 lg->pfn_limit = args[1]; 201 lg->page_offset = args[4]; 202 203 /* We need a complete page for the Guest registers: they are accessible 204 * to the Guest and we can only grant it access to whole pages. */ 205 lg->regs_page = get_zeroed_page(GFP_KERNEL); 206 if (!lg->regs_page) { 207 err = -ENOMEM; 208 goto release_guest; 209 } 210 /* We actually put the registers at the bottom of the page. */ 211 lg->regs = (void *)lg->regs_page + PAGE_SIZE - sizeof(*lg->regs); 212 213 /* Initialize the Guest's shadow page tables, using the toplevel 214 * address the Launcher gave us. This allocates memory, so can 215 * fail. */ 216 err = init_guest_pagetable(lg, args[2]); 217 if (err) 218 goto free_regs; 219 220 /* Now we initialize the Guest's registers, handing it the start 221 * address. */ 222 setup_regs(lg->regs, args[3]); 223 224 /* There are a couple of GDT entries the Guest expects when first 225 * booting. */ 226 setup_guest_gdt(lg); 227 228 /* The timer for lguest's clock needs initialization. */ 229 init_clockdev(lg); 230 231 /* We keep a pointer to the Launcher task (ie. current task) for when 232 * other Guests want to wake this one (inter-Guest I/O). */ 233 lg->tsk = current; 234 /* We need to keep a pointer to the Launcher's memory map, because if 235 * the Launcher dies we need to clean it up. If we don't keep a 236 * reference, it is destroyed before close() is called. */ 237 lg->mm = get_task_mm(lg->tsk); 238 239 /* Initialize the queue for the waker to wait on */ 240 init_waitqueue_head(&lg->break_wq); 241 242 /* We remember which CPU's pages this Guest used last, for optimization 243 * when the same Guest runs on the same CPU twice. */ 244 lg->last_pages = NULL; 245 246 /* We keep our "struct lguest" in the file's private_data. */ 247 file->private_data = lg; 248 249 mutex_unlock(&lguest_lock); 250 251 /* And because this is a write() call, we return the length used. */ 252 return sizeof(args); 253 254free_regs: 255 free_page(lg->regs_page); 256release_guest: 257 memset(lg, 0, sizeof(*lg)); 258unlock: 259 mutex_unlock(&lguest_lock); 260 return err; 261} 262 263/*L:010 The first operation the Launcher does must be a write. All writes 264 * start with a 32 bit number: for the first write this must be 265 * LHREQ_INITIALIZE to set up the Guest. After that the Launcher can use 266 * writes of other values to get DMA buffers and send interrupts. */ 267static ssize_t write(struct file *file, const char __user *input, 268 size_t size, loff_t *off) 269{ 270 /* Once the guest is initialized, we hold the "struct lguest" in the 271 * file private data. */ 272 struct lguest *lg = file->private_data; 273 u32 req; 274 275 if (get_user(req, input) != 0) 276 return -EFAULT; 277 input += sizeof(req); 278 279 /* If you haven't initialized, you must do that first. */ 280 if (req != LHREQ_INITIALIZE && !lg) 281 return -EINVAL; 282 283 /* Once the Guest is dead, all you can do is read() why it died. */ 284 if (lg && lg->dead) 285 return -ENOENT; 286 287 /* If you're not the task which owns the Guest, you can only break */ 288 if (lg && current != lg->tsk && req != LHREQ_BREAK) 289 return -EPERM; 290 291 switch (req) { 292 case LHREQ_INITIALIZE: 293 return initialize(file, (const u32 __user *)input); 294 case LHREQ_GETDMA: 295 return user_get_dma(lg, (const u32 __user *)input); 296 case LHREQ_IRQ: 297 return user_send_irq(lg, (const u32 __user *)input); 298 case LHREQ_BREAK: 299 return break_guest_out(lg, (const u32 __user *)input); 300 default: 301 return -EINVAL; 302 } 303} 304 305/*L:060 The final piece of interface code is the close() routine. It reverses 306 * everything done in initialize(). This is usually called because the 307 * Launcher exited. 308 * 309 * Note that the close routine returns 0 or a negative error number: it can't 310 * really fail, but it can whine. I blame Sun for this wart, and K&R C for 311 * letting them do it. :*/ 312static int close(struct inode *inode, struct file *file) 313{ 314 struct lguest *lg = file->private_data; 315 316 /* If we never successfully initialized, there's nothing to clean up */ 317 if (!lg) 318 return 0; 319 320 /* We need the big lock, to protect from inter-guest I/O and other 321 * Launchers initializing guests. */ 322 mutex_lock(&lguest_lock); 323 /* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */ 324 hrtimer_cancel(&lg->hrt); 325 /* Free any DMA buffers the Guest had bound. */ 326 release_all_dma(lg); 327 /* Free up the shadow page tables for the Guest. */ 328 free_guest_pagetable(lg); 329 /* Now all the memory cleanups are done, it's safe to release the 330 * Launcher's memory management structure. */ 331 mmput(lg->mm); 332 /* If lg->dead doesn't contain an error code it will be NULL or a 333 * kmalloc()ed string, either of which is ok to hand to kfree(). */ 334 if (!IS_ERR(lg->dead)) 335 kfree(lg->dead); 336 /* We can free up the register page we allocated. */ 337 free_page(lg->regs_page); 338 /* We clear the entire structure, which also marks it as free for the 339 * next user. */ 340 memset(lg, 0, sizeof(*lg)); 341 /* Release lock and exit. */ 342 mutex_unlock(&lguest_lock); 343 344 return 0; 345} 346 347/*L:000 348 * Welcome to our journey through the Launcher! 349 * 350 * The Launcher is the Host userspace program which sets up, runs and services 351 * the Guest. In fact, many comments in the Drivers which refer to "the Host" 352 * doing things are inaccurate: the Launcher does all the device handling for 353 * the Guest. The Guest can't tell what's done by the the Launcher and what by 354 * the Host. 355 * 356 * Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we 357 * shall see more of that later. 358 * 359 * We begin our understanding with the Host kernel interface which the Launcher 360 * uses: reading and writing a character device called /dev/lguest. All the 361 * work happens in the read(), write() and close() routines: */ 362static struct file_operations lguest_fops = { 363 .owner = THIS_MODULE, 364 .release = close, 365 .write = write, 366 .read = read, 367}; 368 369/* This is a textbook example of a "misc" character device. Populate a "struct 370 * miscdevice" and register it with misc_register(). */ 371static struct miscdevice lguest_dev = { 372 .minor = MISC_DYNAMIC_MINOR, 373 .name = "lguest", 374 .fops = &lguest_fops, 375}; 376 377int __init lguest_device_init(void) 378{ 379 return misc_register(&lguest_dev); 380} 381 382void __exit lguest_device_remove(void) 383{ 384 misc_deregister(&lguest_dev); 385} 386