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>
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
15 static long user_get_dma(struct lguest *lg, const unsigned long __user *input)
17 unsigned long key, udma, irq;
19 /* Fetch the key they wrote to us. */
20 if (get_user(key, input) != 0)
22 /* Look for a free Guest DMA buffer bound to that key. */
23 udma = get_dma_buffer(lg, key, &irq);
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);
31 /* The (guest-physical) address of the DMA buffer is returned from
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)
43 /* Fetch whether they're turning break on or off.. */
44 if (get_user(on, input) != 0)
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);
55 wake_up(&lg->break_wq);
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)
66 if (get_user(irq, input) != 0)
68 if (irq >= LGUEST_IRQS)
70 /* Next time the Guest runs, the core code will see if it can deliver
72 set_bit(irq, lg->irqs_pending);
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)
80 struct lguest *lg = file->private_data;
82 /* You must write LHREQ_INITIALIZE first! */
86 /* If you're not the task which owns the guest, go away. */
87 if (current != lg->tsk)
90 /* If the guest is already dead, we indicate why */
94 /* lg->dead either contains an error code, or a string. */
96 return PTR_ERR(lg->dead);
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)
105 /* If we returned from read() last time because the Guest sent DMA,
107 if (lg->dma_is_pending)
108 lg->dma_is_pending = 0;
110 /* Run the Guest until something interesting happens. */
111 return run_guest(lg, (unsigned long __user *)user);
114 /*L:020 The initialization write supplies 4 pointer sized (32 or 64 bit)
115 * values (in addition to the LHREQ_INITIALIZE value). These are:
117 * base: The start of the Guest-physical memory inside the Launcher memory.
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.
123 * pgdir: The (Guest-physical) address of the top of the initial Guest
124 * pagetables (which are set up by the Launcher).
126 * start: The first instruction to execute ("eip" in x86-speak).
128 static int initialize(struct file *file, const unsigned long __user *input)
130 /* "struct lguest" contains everything we (the Host) know about a
134 unsigned long args[4];
136 /* We grab the Big Lguest lock, which protects against multiple
137 * simultaneous initializations. */
138 mutex_lock(&lguest_lock);
139 /* You can't initialize twice! Close the device and start again... */
140 if (file->private_data) {
145 if (copy_from_user(args, input, sizeof(args)) != 0) {
150 lg = kzalloc(sizeof(*lg), GFP_KERNEL);
156 /* Populate the easy fields of our "struct lguest" */
157 lg->mem_base = (void __user *)(long)args[0];
158 lg->pfn_limit = args[1];
160 /* We need a complete page for the Guest registers: they are accessible
161 * to the Guest and we can only grant it access to whole pages. */
162 lg->regs_page = get_zeroed_page(GFP_KERNEL);
163 if (!lg->regs_page) {
167 /* We actually put the registers at the bottom of the page. */
168 lg->regs = (void *)lg->regs_page + PAGE_SIZE - sizeof(*lg->regs);
170 /* Initialize the Guest's shadow page tables, using the toplevel
171 * address the Launcher gave us. This allocates memory, so can
173 err = init_guest_pagetable(lg, args[2]);
177 /* Now we initialize the Guest's registers, handing it the start
179 lguest_arch_setup_regs(lg, args[3]);
181 /* The timer for lguest's clock needs initialization. */
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). */
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);
192 /* Initialize the queue for the waker to wait on */
193 init_waitqueue_head(&lg->break_wq);
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;
199 /* We keep our "struct lguest" in the file's private_data. */
200 file->private_data = lg;
202 mutex_unlock(&lguest_lock);
204 /* And because this is a write() call, we return the length used. */
208 free_page(lg->regs_page);
210 memset(lg, 0, sizeof(*lg));
212 mutex_unlock(&lguest_lock);
216 /*L:010 The first operation the Launcher does must be a write. All writes
217 * start with a 32 bit 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 get DMA buffers and send interrupts. */
220 static ssize_t write(struct file *file, const char __user *in,
221 size_t size, loff_t *off)
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;
229 if (get_user(req, input) != 0)
233 /* If you haven't initialized, you must do that first. */
234 if (req != LHREQ_INITIALIZE && !lg)
237 /* Once the Guest is dead, all you can do is read() why it died. */
241 /* If you're not the task which owns the Guest, you can only break */
242 if (lg && current != lg->tsk && req != LHREQ_BREAK)
246 case LHREQ_INITIALIZE:
247 return initialize(file, input);
249 return user_get_dma(lg, input);
251 return user_send_irq(lg, input);
253 return break_guest_out(lg, input);
259 /*L:060 The final piece of interface code is the close() routine. It reverses
260 * everything done in initialize(). This is usually called because the
263 * Note that the close routine returns 0 or a negative error number: it can't
264 * really fail, but it can whine. I blame Sun for this wart, and K&R C for
265 * letting them do it. :*/
266 static int close(struct inode *inode, struct file *file)
268 struct lguest *lg = file->private_data;
270 /* If we never successfully initialized, there's nothing to clean up */
274 /* We need the big lock, to protect from inter-guest I/O and other
275 * Launchers initializing guests. */
276 mutex_lock(&lguest_lock);
277 /* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */
278 hrtimer_cancel(&lg->hrt);
279 /* Free any DMA buffers the Guest had bound. */
281 /* Free up the shadow page tables for the Guest. */
282 free_guest_pagetable(lg);
283 /* Now all the memory cleanups are done, it's safe to release the
284 * Launcher's memory management structure. */
286 /* If lg->dead doesn't contain an error code it will be NULL or a
287 * kmalloc()ed string, either of which is ok to hand to kfree(). */
288 if (!IS_ERR(lg->dead))
290 /* We can free up the register page we allocated. */
291 free_page(lg->regs_page);
292 /* We clear the entire structure, which also marks it as free for the
294 memset(lg, 0, sizeof(*lg));
295 /* Release lock and exit. */
296 mutex_unlock(&lguest_lock);
302 * Welcome to our journey through the Launcher!
304 * The Launcher is the Host userspace program which sets up, runs and services
305 * the Guest. In fact, many comments in the Drivers which refer to "the Host"
306 * doing things are inaccurate: the Launcher does all the device handling for
307 * the Guest. The Guest can't tell what's done by the the Launcher and what by
310 * Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we
311 * shall see more of that later.
313 * We begin our understanding with the Host kernel interface which the Launcher
314 * uses: reading and writing a character device called /dev/lguest. All the
315 * work happens in the read(), write() and close() routines: */
316 static struct file_operations lguest_fops = {
317 .owner = THIS_MODULE,
323 /* This is a textbook example of a "misc" character device. Populate a "struct
324 * miscdevice" and register it with misc_register(). */
325 static struct miscdevice lguest_dev = {
326 .minor = MISC_DYNAMIC_MINOR,
328 .fops = &lguest_fops,
331 int __init lguest_device_init(void)
333 return misc_register(&lguest_dev);
336 void __exit lguest_device_remove(void)
338 misc_deregister(&lguest_dev);