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