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: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.
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. */
17 static void setup_regs(struct lguest_regs *regs, unsigned long start)
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.
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;
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. */
35 /* The "Extended Instruction Pointer" register says where the Guest is
39 /* %esi points to our boot information, at physical address 0, so don't
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
46 static long user_get_dma(struct lguest *lg, const u32 __user *input)
48 unsigned long key, udma, irq;
50 /* Fetch the key they wrote to us. */
51 if (get_user(key, input) != 0)
53 /* Look for a free Guest DMA buffer bound to that key. */
54 udma = get_dma_buffer(lg, key, &irq);
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);
62 /* The (guest-physical) address of the DMA buffer is returned from
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. */
70 static int break_guest_out(struct lguest *lg, const u32 __user *input)
74 /* Fetch whether they're turning break on or off.. */
75 if (get_user(on, input) != 0)
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);
86 wake_up(&lg->break_wq);
91 /*L:050 Sending an interrupt is done by writing LHREQ_IRQ and an interrupt
92 * number to /dev/lguest. */
93 static int user_send_irq(struct lguest *lg, const u32 __user *input)
97 if (get_user(irq, input) != 0)
99 if (irq >= LGUEST_IRQS)
101 /* Next time the Guest runs, the core code will see if it can deliver
103 set_bit(irq, lg->irqs_pending);
107 /*L:040 Once our Guest is initialized, the Launcher makes it run by reading
108 * from /dev/lguest. */
109 static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
111 struct lguest *lg = file->private_data;
113 /* You must write LHREQ_INITIALIZE first! */
117 /* If you're not the task which owns the guest, go away. */
118 if (current != lg->tsk)
121 /* If the guest is already dead, we indicate why */
125 /* lg->dead either contains an error code, or a string. */
126 if (IS_ERR(lg->dead))
127 return PTR_ERR(lg->dead);
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)
136 /* If we returned from read() last time because the Guest sent DMA,
138 if (lg->dma_is_pending)
139 lg->dma_is_pending = 0;
141 /* Run the Guest until something interesting happens. */
142 return run_guest(lg, (unsigned long __user *)user);
145 /*L:020 The initialization write supplies 5 32-bit values (in addition to the
146 * 32-bit LHREQ_INITIALIZE value). These are:
148 * base: The start of the Guest-physical memory inside the Launcher memory.
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.
154 * pgdir: The (Guest-physical) address of the top of the initial Guest
155 * pagetables (which are set up by the Launcher).
157 * start: The first instruction to execute ("eip" in x86-speak).
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.
165 static int initialize(struct file *file, const u32 __user *input)
167 /* "struct lguest" contains everything we (the Host) know about a
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) {
182 if (copy_from_user(args, input, sizeof(args)) != 0) {
187 /* Find an unused guest. */
188 i = find_free_guest();
193 /* OK, we have an index into the "lguest" array: "lg" is a convenient
197 /* Populate the easy fields of our "struct lguest" */
199 lg->mem_base = (void __user *)(long)args[0];
200 lg->pfn_limit = args[1];
201 lg->page_offset = args[4];
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) {
210 /* We actually put the registers at the bottom of the page. */
211 lg->regs = (void *)lg->regs_page + PAGE_SIZE - sizeof(*lg->regs);
213 /* Initialize the Guest's shadow page tables, using the toplevel
214 * address the Launcher gave us. This allocates memory, so can
216 err = init_guest_pagetable(lg, args[2]);
220 /* Now we initialize the Guest's registers, handing it the start
222 setup_regs(lg->regs, args[3]);
224 /* There are a couple of GDT entries the Guest expects when first
228 /* The timer for lguest's clock needs initialization. */
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). */
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);
239 /* Initialize the queue for the waker to wait on */
240 init_waitqueue_head(&lg->break_wq);
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;
246 /* We keep our "struct lguest" in the file's private_data. */
247 file->private_data = lg;
249 mutex_unlock(&lguest_lock);
251 /* And because this is a write() call, we return the length used. */
255 free_page(lg->regs_page);
257 memset(lg, 0, sizeof(*lg));
259 mutex_unlock(&lguest_lock);
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. */
267 static ssize_t write(struct file *file, const char __user *input,
268 size_t size, loff_t *off)
270 /* Once the guest is initialized, we hold the "struct lguest" in the
271 * file private data. */
272 struct lguest *lg = file->private_data;
275 if (get_user(req, input) != 0)
277 input += sizeof(req);
279 /* If you haven't initialized, you must do that first. */
280 if (req != LHREQ_INITIALIZE && !lg)
283 /* Once the Guest is dead, all you can do is read() why it died. */
287 /* If you're not the task which owns the Guest, you can only break */
288 if (lg && current != lg->tsk && req != LHREQ_BREAK)
292 case LHREQ_INITIALIZE:
293 return initialize(file, (const u32 __user *)input);
295 return user_get_dma(lg, (const u32 __user *)input);
297 return user_send_irq(lg, (const u32 __user *)input);
299 return break_guest_out(lg, (const u32 __user *)input);
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
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. :*/
312 static int close(struct inode *inode, struct file *file)
314 struct lguest *lg = file->private_data;
316 /* If we never successfully initialized, there's nothing to clean up */
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. */
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. */
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))
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
340 memset(lg, 0, sizeof(*lg));
341 /* Release lock and exit. */
342 mutex_unlock(&lguest_lock);
348 * Welcome to our journey through the Launcher!
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
356 * Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we
357 * shall see more of that later.
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: */
362 static struct file_operations lguest_fops = {
363 .owner = THIS_MODULE,
369 /* This is a textbook example of a "misc" character device. Populate a "struct
370 * miscdevice" and register it with misc_register(). */
371 static struct miscdevice lguest_dev = {
372 .minor = MISC_DYNAMIC_MINOR,
374 .fops = &lguest_fops,
377 int __init lguest_device_init(void)
379 return misc_register(&lguest_dev);
382 void __exit lguest_device_remove(void)
384 misc_deregister(&lguest_dev);