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 <linux/sched.h>
  10 #include "lg.h"
  11
  12 /*L:055 When something happens, the Waker process needs a way to stop the
  13  * kernel running the Guest and return to the Launcher.  So the Waker writes
  14  * LHREQ_BREAK and the value "1" to /dev/lguest to do this.  Once the Launcher
  15  * has done whatever needs attention, it writes LHREQ_BREAK and "0" to release
  16  * the Waker. */
  17 static int break_guest_out(struct lg_cpu *cpu, const unsigned long __user*input)
  18 {
  19         unsigned long on;
  20
  21         /* Fetch whether they're turning break on or off. */
  22         if (get_user(on, input) != 0)
  23                 return -EFAULT;
  24
  25         if (on) {
  26                 cpu->break_out = 1;
  27                 /* Pop it out of the Guest (may be running on different CPU) */
  28                 wake_up_process(cpu->tsk);
  29                 /* Wait for them to reset it */
  30                 return wait_event_interruptible(cpu->break_wq, !cpu->break_out);
  31         } else {
  32                 cpu->break_out = 0;
  33                 wake_up(&cpu->break_wq);
  34                 return 0;
  35         }
  36 }
  37
  38 /*L:050 Sending an interrupt is done by writing LHREQ_IRQ and an interrupt
  39  * number to /dev/lguest. */
  40 static int user_send_irq(struct lg_cpu *cpu, const unsigned long __user *input)
  41 {
  42         unsigned long irq;
  43
  44         if (get_user(irq, input) != 0)
  45                 return -EFAULT;
  46         if (irq >= LGUEST_IRQS)
  47                 return -EINVAL;
  48         /* Next time the Guest runs, the core code will see if it can deliver
  49          * this interrupt. */
  50         set_bit(irq, cpu->irqs_pending);
  51         return 0;
  52 }
  53
  54 /*L:040 Once our Guest is initialized, the Launcher makes it run by reading
  55  * from /dev/lguest. */
  56 static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
  57 {
  58         struct lguest *lg = file->private_data;
  59         struct lg_cpu *cpu;
  60         unsigned int cpu_id = *o;
  61
  62         /* You must write LHREQ_INITIALIZE first! */
  63         if (!lg)
  64                 return -EINVAL;
  65
  66         /* Watch out for arbitrary vcpu indexes! */
  67         if (cpu_id >= lg->nr_cpus)
  68                 return -EINVAL;
  69
  70         cpu = &lg->cpus[cpu_id];
  71
  72         /* If you're not the task which owns the Guest, go away. */
  73         if (current != cpu->tsk)
  74                 return -EPERM;
  75
  76         /* If the Guest is already dead, we indicate why */
  77         if (lg->dead) {
  78                 size_t len;
  79
  80                 /* lg->dead either contains an error code, or a string. */
  81                 if (IS_ERR(lg->dead))
  82                         return PTR_ERR(lg->dead);
  83
  84                 /* We can only return as much as the buffer they read with. */
  85                 len = min(size, strlen(lg->dead)+1);
  86                 if (copy_to_user(user, lg->dead, len) != 0)
  87                         return -EFAULT;
  88                 return len;
  89         }
  90
  91         /* If we returned from read() last time because the Guest sent I/O,
  92          * clear the flag. */
  93         if (cpu->pending_notify)
  94                 cpu->pending_notify = 0;
  95
  96         /* Run the Guest until something interesting happens. */
  97         return run_guest(cpu, (unsigned long __user *)user);
  98 }
  99
 100 /*L:025 This actually initializes a CPU.  For the moment, a Guest is only
 101  * uniprocessor, so "id" is always 0. */
 102 static int lg_cpu_start(struct lg_cpu *cpu, unsigned id, unsigned long start_ip)
 103 {
 104         /* We have a limited number the number of CPUs in the lguest struct. */
 105         if (id >= ARRAY_SIZE(cpu->lg->cpus))
 106                 return -EINVAL;
 107
 108         /* Set up this CPU's id, and pointer back to the lguest struct. */
 109         cpu->id = id;
 110         cpu->lg = container_of((cpu - id), struct lguest, cpus[0]);
 111         cpu->lg->nr_cpus++;
 112
 113         /* Each CPU has a timer it can set. */
 114         init_clockdev(cpu);
 115
 116         /* We need a complete page for the Guest registers: they are accessible
 117          * to the Guest and we can only grant it access to whole pages. */
 118         cpu->regs_page = get_zeroed_page(GFP_KERNEL);
 119         if (!cpu->regs_page)
 120                 return -ENOMEM;
 121
 122         /* We actually put the registers at the bottom of the page. */
 123         cpu->regs = (void *)cpu->regs_page + PAGE_SIZE - sizeof(*cpu->regs);
 124
 125         /* Now we initialize the Guest's registers, handing it the start
 126          * address. */
 127         lguest_arch_setup_regs(cpu, start_ip);
 128
 129         /* Initialize the queue for the Waker to wait on */
 130         init_waitqueue_head(&cpu->break_wq);
 131
 132         /* We keep a pointer to the Launcher task (ie. current task) for when
 133          * other Guests want to wake this one (eg. console input). */
 134         cpu->tsk = current;
 135
 136         /* We need to keep a pointer to the Launcher's memory map, because if
 137          * the Launcher dies we need to clean it up.  If we don't keep a
 138          * reference, it is destroyed before close() is called. */
 139         cpu->mm = get_task_mm(cpu->tsk);
 140
 141         /* We remember which CPU's pages this Guest used last, for optimization
 142          * when the same Guest runs on the same CPU twice. */
 143         cpu->last_pages = NULL;
 144
 145         /* No error == success. */
 146         return 0;
 147 }
 148
 149 /*L:020 The initialization write supplies 4 pointer sized (32 or 64 bit)
 150  * values (in addition to the LHREQ_INITIALIZE value).  These are:
 151  *
 152  * base: The start of the Guest-physical memory inside the Launcher memory.
 153  *
 154  * pfnlimit: The highest (Guest-physical) page number the Guest should be
 155  * allowed to access.  The Guest memory lives inside the Launcher, so it sets
 156  * this to ensure the Guest can only reach its own memory.
 157  *
 158  * pgdir: The (Guest-physical) address of the top of the initial Guest
 159  * pagetables (which are set up by the Launcher).
 160  *
 161  * start: The first instruction to execute ("eip" in x86-speak).
 162  */
 163 static int initialize(struct file *file, const unsigned long __user *input)
 164 {
 165         /* "struct lguest" contains everything we (the Host) know about a
 166          * Guest. */
 167         struct lguest *lg;
 168         int err;
 169         unsigned long args[4];
 170
 171         /* We grab the Big Lguest lock, which protects against multiple
 172          * simultaneous initializations. */
 173         mutex_lock(&lguest_lock);
 174         /* You can't initialize twice!  Close the device and start again... */
 175         if (file->private_data) {
 176                 err = -EBUSY;
 177                 goto unlock;
 178         }
 179
 180         if (copy_from_user(args, input, sizeof(args)) != 0) {
 181                 err = -EFAULT;
 182                 goto unlock;
 183         }
 184
 185         lg = kzalloc(sizeof(*lg), GFP_KERNEL);
 186         if (!lg) {
 187                 err = -ENOMEM;
 188                 goto unlock;
 189         }
 190
 191         /* Populate the easy fields of our "struct lguest" */
 192         lg->mem_base = (void __user *)args[0];
 193         lg->pfn_limit = args[1];
 194
 195         /* This is the first cpu (cpu 0) and it will start booting at args[3] */
 196         err = lg_cpu_start(&lg->cpus[0], 0, args[3]);
 197         if (err)
 198                 goto release_guest;
 199
 200         /* Initialize the Guest's shadow page tables, using the toplevel
 201          * address the Launcher gave us.  This allocates memory, so can fail. */
 202         err = init_guest_pagetable(lg, args[2]);
 203         if (err)
 204                 goto free_regs;
 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         /* FIXME: This should be in free_vcpu */
 216         free_page(lg->cpus[0].regs_page);
 217 release_guest:
 218         kfree(lg);
 219 unlock:
 220         mutex_unlock(&lguest_lock);
 221         return err;
 222 }
 223
 224 /*L:010 The first operation the Launcher does must be a write.  All writes
 225  * start with an unsigned long number: for the first write this must be
 226  * LHREQ_INITIALIZE to set up the Guest.  After that the Launcher can use
 227  * writes of other values to send interrupts.
 228  *
 229  * Note that we overload the "offset" in the /dev/lguest file to indicate what
 230  * CPU number we're dealing with.  Currently this is always 0, since we only
 231  * support uniprocessor Guests, but you can see the beginnings of SMP support
 232  * here. */
 233 static ssize_t write(struct file *file, const char __user *in,
 234                      size_t size, loff_t *off)
 235 {
 236         /* Once the Guest is initialized, we hold the "struct lguest" in the
 237          * file private data. */
 238         struct lguest *lg = file->private_data;
 239         const unsigned long __user *input = (const unsigned long __user *)in;
 240         unsigned long req;
 241         struct lg_cpu *uninitialized_var(cpu);
 242         unsigned int cpu_id = *off;
 243
 244         /* The first value tells us what this request is. */
 245         if (get_user(req, input) != 0)
 246                 return -EFAULT;
 247         input++;
 248
 249         /* If you haven't initialized, you must do that first. */
 250         if (req != LHREQ_INITIALIZE) {
 251                 if (!lg || (cpu_id >= lg->nr_cpus))
 252                         return -EINVAL;
 253                 cpu = &lg->cpus[cpu_id];
 254
 255                 /* Once the Guest is dead, you can only read() why it died. */
 256                 if (lg->dead)
 257                         return -ENOENT;
 258
 259                 /* If you're not the task which owns the Guest, all you can do
 260                  * is break the Launcher out of running the Guest. */
 261                 if (current != cpu->tsk && req != LHREQ_BREAK)
 262                         return -EPERM;
 263         }
 264
 265         switch (req) {
 266         case LHREQ_INITIALIZE:
 267                 return initialize(file, input);
 268         case LHREQ_IRQ:
 269                 return user_send_irq(cpu, input);
 270         case LHREQ_BREAK:
 271                 return break_guest_out(cpu, input);
 272         default:
 273                 return -EINVAL;
 274         }
 275 }
 276
 277 /*L:060 The final piece of interface code is the close() routine.  It reverses
 278  * everything done in initialize().  This is usually called because the
 279  * Launcher exited.
 280  *
 281  * Note that the close routine returns 0 or a negative error number: it can't
 282  * really fail, but it can whine.  I blame Sun for this wart, and K&R C for
 283  * letting them do it. :*/
 284 static int close(struct inode *inode, struct file *file)
 285 {
 286         struct lguest *lg = file->private_data;
 287         unsigned int i;
 288
 289         /* If we never successfully initialized, there's nothing to clean up */
 290         if (!lg)
 291                 return 0;
 292
 293         /* We need the big lock, to protect from inter-guest I/O and other
 294          * Launchers initializing guests. */
 295         mutex_lock(&lguest_lock);
 296
 297         /* Free up the shadow page tables for the Guest. */
 298         free_guest_pagetable(lg);
 299
 300         for (i = 0; i < lg->nr_cpus; i++) {
 301                 /* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */
 302                 hrtimer_cancel(&lg->cpus[i].hrt);
 303                 /* We can free up the register page we allocated. */
 304                 free_page(lg->cpus[i].regs_page);
 305                 /* Now all the memory cleanups are done, it's safe to release
 306                  * the Launcher's memory management structure. */
 307                 mmput(lg->cpus[i].mm);
 308         }
 309         /* If lg->dead doesn't contain an error code it will be NULL or a
 310          * kmalloc()ed string, either of which is ok to hand to kfree(). */
 311         if (!IS_ERR(lg->dead))
 312                 kfree(lg->dead);
 313         /* We clear the entire structure, which also marks it as free for the
 314          * next user. */
 315         memset(lg, 0, sizeof(*lg));
 316         /* Release lock and exit. */
 317         mutex_unlock(&lguest_lock);
 318
 319         return 0;
 320 }
 321
 322 /*L:000
 323  * Welcome to our journey through the Launcher!
 324  *
 325  * The Launcher is the Host userspace program which sets up, runs and services
 326  * the Guest.  In fact, many comments in the Drivers which refer to "the Host"
 327  * doing things are inaccurate: the Launcher does all the device handling for
 328  * the Guest, but the Guest can't know that.
 329  *
 330  * Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we
 331  * shall see more of that later.
 332  *
 333  * We begin our understanding with the Host kernel interface which the Launcher
 334  * uses: reading and writing a character device called /dev/lguest.  All the
 335  * work happens in the read(), write() and close() routines: */
 336 static struct file_operations lguest_fops = {
 337         .owner   = THIS_MODULE,
 338         .release = close,
 339         .write   = write,
 340         .read    = read,
 341 };
 342
 343 /* This is a textbook example of a "misc" character device.  Populate a "struct
 344  * miscdevice" and register it with misc_register(). */
 345 static struct miscdevice lguest_dev = {
 346         .minor  = MISC_DYNAMIC_MINOR,
 347         .name   = "lguest",
 348         .fops   = &lguest_fops,
 349 };
 350
 351 int __init lguest_device_init(void)
 352 {
 353         return misc_register(&lguest_dev);
 354 }
 355
 356 void __exit lguest_device_remove(void)
 357 {
 358         misc_deregister(&lguest_dev);
 359 }