drivers/lguest/lguest_user.c

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