/*P:200 This contains all the /dev/lguest code, whereby the userspace launcher * controls and communicates with the Guest. For example, the first write will * tell us the Guest's memory layout, pagetable, entry point and kernel address * offset. A read will run the Guest until something happens, such as a signal * or the Guest doing a NOTIFY out to the Launcher. :*/ #include <linux/uaccess.h> #include <linux/miscdevice.h> #include <linux/fs.h> #include "lg.h" /*L:055 When something happens, the Waker process needs a way to stop the * kernel running the Guest and return to the Launcher. So the Waker writes * LHREQ_BREAK and the value "1" to /dev/lguest to do this. Once the Launcher * has done whatever needs attention, it writes LHREQ_BREAK and "0" to release * the Waker. */ static int break_guest_out(struct lguest *lg, const unsigned long __user *input) { unsigned long on; /* Fetch whether they're turning break on or off. */ if (get_user(on, input) != 0) return -EFAULT; if (on) { lg->break_out = 1; /* Pop it out of the Guest (may be running on different CPU) */ wake_up_process(lg->tsk); /* Wait for them to reset it */ return wait_event_interruptible(lg->break_wq, !lg->break_out); } else { lg->break_out = 0; wake_up(&lg->break_wq); return 0; } } /*L:050 Sending an interrupt is done by writing LHREQ_IRQ and an interrupt * number to /dev/lguest. */ static int user_send_irq(struct lguest *lg, const unsigned long __user *input) { unsigned long irq; if (get_user(irq, input) != 0) return -EFAULT; if (irq >= LGUEST_IRQS) return -EINVAL; /* Next time the Guest runs, the core code will see if it can deliver * this interrupt. */ set_bit(irq, lg->irqs_pending); return 0; } /*L:040 Once our Guest is initialized, the Launcher makes it run by reading * from /dev/lguest. */ static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o) { struct lguest *lg = file->private_data; /* You must write LHREQ_INITIALIZE first! */ if (!lg) return -EINVAL; /* If you're not the task which owns the Guest, go away. */ if (current != lg->tsk) return -EPERM; /* If the guest is already dead, we indicate why */ if (lg->dead) { size_t len; /* lg->dead either contains an error code, or a string. */ if (IS_ERR(lg->dead)) return PTR_ERR(lg->dead); /* We can only return as much as the buffer they read with. */ len = min(size, strlen(lg->dead)+1); if (copy_to_user(user, lg->dead, len) != 0) return -EFAULT; return len; } /* If we returned from read() last time because the Guest notified, * clear the flag. */ if (lg->pending_notify) lg->pending_notify = 0; /* Run the Guest until something interesting happens. */ return run_guest(lg, (unsigned long __user *)user); } /*L:020 The initialization write supplies 4 pointer sized (32 or 64 bit) * values (in addition to the LHREQ_INITIALIZE value). These are: * * base: The start of the Guest-physical memory inside the Launcher memory. * * pfnlimit: The highest (Guest-physical) page number the Guest should be * allowed to access. The Guest memory lives inside the Launcher, so it sets * this to ensure the Guest can only reach its own memory. * * pgdir: The (Guest-physical) address of the top of the initial Guest * pagetables (which are set up by the Launcher). * * start: The first instruction to execute ("eip" in x86-speak). */ static int initialize(struct file *file, const unsigned long __user *input) { /* "struct lguest" contains everything we (the Host) know about a * Guest. */ struct lguest *lg; int err; unsigned long args[4]; /* We grab the Big Lguest lock, which protects against multiple * simultaneous initializations. */ mutex_lock(&lguest_lock); /* You can't initialize twice! Close the device and start again... */ if (file->private_data) { err = -EBUSY; goto unlock; } if (copy_from_user(args, input, sizeof(args)) != 0) { err = -EFAULT; goto unlock; } lg = kzalloc(sizeof(*lg), GFP_KERNEL); if (!lg) { err = -ENOMEM; goto unlock; } /* Populate the easy fields of our "struct lguest" */ lg->mem_base = (void __user *)(long)args[0]; lg->pfn_limit = args[1]; /* We need a complete page for the Guest registers: they are accessible * to the Guest and we can only grant it access to whole pages. */ lg->regs_page = get_zeroed_page(GFP_KERNEL); if (!lg->regs_page) { err = -ENOMEM; goto release_guest; } /* We actually put the registers at the bottom of the page. */ lg->regs = (void *)lg->regs_page + PAGE_SIZE - sizeof(*lg->regs); /* Initialize the Guest's shadow page tables, using the toplevel * address the Launcher gave us. This allocates memory, so can * fail. */ err = init_guest_pagetable(lg, args[2]); if (err) goto free_regs; /* Now we initialize the Guest's registers, handing it the start * address. */ lguest_arch_setup_regs(lg, args[3]); /* The timer for lguest's clock needs initialization. */ init_clockdev(lg); /* We keep a pointer to the Launcher task (ie. current task) for when * other Guests want to wake this one (inter-Guest I/O). */ lg->tsk = current; /* We need to keep a pointer to the Launcher's memory map, because if * the Launcher dies we need to clean it up. If we don't keep a * reference, it is destroyed before close() is called. */ lg->mm = get_task_mm(lg->tsk); /* Initialize the queue for the waker to wait on */ init_waitqueue_head(&lg->break_wq); /* We remember which CPU's pages this Guest used last, for optimization * when the same Guest runs on the same CPU twice. */ lg->last_pages = NULL; /* We keep our "struct lguest" in the file's private_data. */ file->private_data = lg; mutex_unlock(&lguest_lock); /* And because this is a write() call, we return the length used. */ return sizeof(args); free_regs: free_page(lg->regs_page); release_guest: kfree(lg); unlock: mutex_unlock(&lguest_lock); return err; } /*L:010 The first operation the Launcher does must be a write. All writes * start with an unsigned long number: for the first write this must be * LHREQ_INITIALIZE to set up the Guest. After that the Launcher can use * writes of other values to send interrupts. */ static ssize_t write(struct file *file, const char __user *in, size_t size, loff_t *off) { /* Once the guest is initialized, we hold the "struct lguest" in the * file private data. */ struct lguest *lg = file->private_data; const unsigned long __user *input = (const unsigned long __user *)in; unsigned long req; if (get_user(req, input) != 0) return -EFAULT; input++; /* If you haven't initialized, you must do that first. */ if (req != LHREQ_INITIALIZE && !lg) return -EINVAL; /* Once the Guest is dead, all you can do is read() why it died. */ if (lg && lg->dead) return -ENOENT; /* If you're not the task which owns the Guest, you can only break */ if (lg && current != lg->tsk && req != LHREQ_BREAK) return -EPERM; switch (req) { case LHREQ_INITIALIZE: return initialize(file, input); case LHREQ_IRQ: return user_send_irq(lg, input); case LHREQ_BREAK: return break_guest_out(lg, input); default: return -EINVAL; } } /*L:060 The final piece of interface code is the close() routine. It reverses * everything done in initialize(). This is usually called because the * Launcher exited. * * Note that the close routine returns 0 or a negative error number: it can't * really fail, but it can whine. I blame Sun for this wart, and K&R C for * letting them do it. :*/ static int close(struct inode *inode, struct file *file) { struct lguest *lg = file->private_data; /* If we never successfully initialized, there's nothing to clean up */ if (!lg) return 0; /* We need the big lock, to protect from inter-guest I/O and other * Launchers initializing guests. */ mutex_lock(&lguest_lock); /* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */ hrtimer_cancel(&lg->hrt); /* Free up the shadow page tables for the Guest. */ free_guest_pagetable(lg); /* Now all the memory cleanups are done, it's safe to release the * Launcher's memory management structure. */ mmput(lg->mm); /* If lg->dead doesn't contain an error code it will be NULL or a * kmalloc()ed string, either of which is ok to hand to kfree(). */ if (!IS_ERR(lg->dead)) kfree(lg->dead); /* We can free up the register page we allocated. */ free_page(lg->regs_page); /* We clear the entire structure, which also marks it as free for the * next user. */ memset(lg, 0, sizeof(*lg)); /* Release lock and exit. */ mutex_unlock(&lguest_lock); return 0; } /*L:000 * Welcome to our journey through the Launcher! * * The Launcher is the Host userspace program which sets up, runs and services * the Guest. In fact, many comments in the Drivers which refer to "the Host" * doing things are inaccurate: the Launcher does all the device handling for * the Guest, but the Guest can't know that. * * Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we * shall see more of that later. * * We begin our understanding with the Host kernel interface which the Launcher * uses: reading and writing a character device called /dev/lguest. All the * work happens in the read(), write() and close() routines: */ static struct file_operations lguest_fops = { .owner = THIS_MODULE, .release = close, .write = write, .read = read, }; /* This is a textbook example of a "misc" character device. Populate a "struct * miscdevice" and register it with misc_register(). */ static struct miscdevice lguest_dev = { .minor = MISC_DYNAMIC_MINOR, .name = "lguest", .fops = &lguest_fops, }; int __init lguest_device_init(void) { return misc_register(&lguest_dev); } void __exit lguest_device_remove(void) { misc_deregister(&lguest_dev); }