diff options
Diffstat (limited to 'drivers/lguest/lguest_user.c')
| -rw-r--r-- | drivers/lguest/lguest_user.c | 542 |
1 files changed, 542 insertions, 0 deletions
diff --git a/drivers/lguest/lguest_user.c b/drivers/lguest/lguest_user.c new file mode 100644 index 00000000..ff4a0bc9 --- /dev/null +++ b/drivers/lguest/lguest_user.c @@ -0,0 +1,542 @@ +/*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 and entry + * point. A read will run the Guest until something happens, such as + * a signal or the Guest doing a NOTIFY out to the Launcher. There is + * also a way for the Launcher to attach eventfds to particular NOTIFY + * values instead of returning from the read() call. +:*/ +#include <linux/uaccess.h> +#include <linux/miscdevice.h> +#include <linux/fs.h> +#include <linux/sched.h> +#include <linux/eventfd.h> +#include <linux/file.h> +#include <linux/slab.h> +#include <linux/export.h> +#include "lg.h" + +/*L:056 + * Before we move on, let's jump ahead and look at what the kernel does when + * it needs to look up the eventfds. That will complete our picture of how we + * use RCU. + * + * The notification value is in cpu->pending_notify: we return true if it went + * to an eventfd. + */ +bool send_notify_to_eventfd(struct lg_cpu *cpu) +{ + unsigned int i; + struct lg_eventfd_map *map; + + /* + * This "rcu_read_lock()" helps track when someone is still looking at + * the (RCU-using) eventfds array. It's not actually a lock at all; + * indeed it's a noop in many configurations. (You didn't expect me to + * explain all the RCU secrets here, did you?) + */ + rcu_read_lock(); + /* + * rcu_dereference is the counter-side of rcu_assign_pointer(); it + * makes sure we don't access the memory pointed to by + * cpu->lg->eventfds before cpu->lg->eventfds is set. Sounds crazy, + * but Alpha allows this! Paul McKenney points out that a really + * aggressive compiler could have the same effect: + * http://lists.ozlabs.org/pipermail/lguest/2009-July/001560.html + * + * So play safe, use rcu_dereference to get the rcu-protected pointer: + */ + map = rcu_dereference(cpu->lg->eventfds); + /* + * Simple array search: even if they add an eventfd while we do this, + * we'll continue to use the old array and just won't see the new one. + */ + for (i = 0; i < map->num; i++) { + if (map->map[i].addr == cpu->pending_notify) { + eventfd_signal(map->map[i].event, 1); + cpu->pending_notify = 0; + break; + } + } + /* We're done with the rcu-protected variable cpu->lg->eventfds. */ + rcu_read_unlock(); + + /* If we cleared the notification, it's because we found a match. */ + return cpu->pending_notify == 0; +} + +/*L:055 + * One of the more tricksy tricks in the Linux Kernel is a technique called + * Read Copy Update. Since one point of lguest is to teach lguest journeyers + * about kernel coding, I use it here. (In case you're curious, other purposes + * include learning about virtualization and instilling a deep appreciation for + * simplicity and puppies). + * + * We keep a simple array which maps LHCALL_NOTIFY values to eventfds, but we + * add new eventfds without ever blocking readers from accessing the array. + * The current Launcher only does this during boot, so that never happens. But + * Read Copy Update is cool, and adding a lock risks damaging even more puppies + * than this code does. + * + * We allocate a brand new one-larger array, copy the old one and add our new + * element. Then we make the lg eventfd pointer point to the new array. + * That's the easy part: now we need to free the old one, but we need to make + * sure no slow CPU somewhere is still looking at it. That's what + * synchronize_rcu does for us: waits until every CPU has indicated that it has + * moved on to know it's no longer using the old one. + * + * If that's unclear, see http://en.wikipedia.org/wiki/Read-copy-update. + */ +static int add_eventfd(struct lguest *lg, unsigned long addr, int fd) +{ + struct lg_eventfd_map *new, *old = lg->eventfds; + + /* + * We don't allow notifications on value 0 anyway (pending_notify of + * 0 means "nothing pending"). + */ + if (!addr) + return -EINVAL; + + /* + * Replace the old array with the new one, carefully: others can + * be accessing it at the same time. + */ + new = kmalloc(sizeof(*new) + sizeof(new->map[0]) * (old->num + 1), + GFP_KERNEL); + if (!new) + return -ENOMEM; + + /* First make identical copy. */ + memcpy(new->map, old->map, sizeof(old->map[0]) * old->num); + new->num = old->num; + + /* Now append new entry. */ + new->map[new->num].addr = addr; + new->map[new->num].event = eventfd_ctx_fdget(fd); + if (IS_ERR(new->map[new->num].event)) { + int err = PTR_ERR(new->map[new->num].event); + kfree(new); + return err; + } + new->num++; + + /* + * Now put new one in place: rcu_assign_pointer() is a fancy way of + * doing "lg->eventfds = new", but it uses memory barriers to make + * absolutely sure that the contents of "new" written above is nailed + * down before we actually do the assignment. + * + * We have to think about these kinds of things when we're operating on + * live data without locks. + */ + rcu_assign_pointer(lg->eventfds, new); + + /* + * We're not in a big hurry. Wait until no one's looking at old + * version, then free it. + */ + synchronize_rcu(); + kfree(old); + + return 0; +} + +/*L:052 + * Receiving notifications from the Guest is usually done by attaching a + * particular LHCALL_NOTIFY value to an event filedescriptor. The eventfd will + * become readable when the Guest does an LHCALL_NOTIFY with that value. + * + * This is really convenient for processing each virtqueue in a separate + * thread. + */ +static int attach_eventfd(struct lguest *lg, const unsigned long __user *input) +{ + unsigned long addr, fd; + int err; + + if (get_user(addr, input) != 0) + return -EFAULT; + input++; + if (get_user(fd, input) != 0) + return -EFAULT; + + /* + * Just make sure two callers don't add eventfds at once. We really + * only need to lock against callers adding to the same Guest, so using + * the Big Lguest Lock is overkill. But this is setup, not a fast path. + */ + mutex_lock(&lguest_lock); + err = add_eventfd(lg, addr, fd); + mutex_unlock(&lguest_lock); + + return err; +} + +/*L:050 + * Sending an interrupt is done by writing LHREQ_IRQ and an interrupt + * number to /dev/lguest. + */ +static int user_send_irq(struct lg_cpu *cpu, 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_interrupt(cpu, irq); + 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; + struct lg_cpu *cpu; + unsigned int cpu_id = *o; + + /* You must write LHREQ_INITIALIZE first! */ + if (!lg) + return -EINVAL; + + /* Watch out for arbitrary vcpu indexes! */ + if (cpu_id >= lg->nr_cpus) + return -EINVAL; + + cpu = &lg->cpus[cpu_id]; + + /* If you're not the task which owns the Guest, go away. */ + if (current != cpu->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 sent I/O, + * clear the flag. + */ + if (cpu->pending_notify) + cpu->pending_notify = 0; + + /* Run the Guest until something interesting happens. */ + return run_guest(cpu, (unsigned long __user *)user); +} + +/*L:025 + * This actually initializes a CPU. For the moment, a Guest is only + * uniprocessor, so "id" is always 0. + */ +static int lg_cpu_start(struct lg_cpu *cpu, unsigned id, unsigned long start_ip) +{ + /* We have a limited number the number of CPUs in the lguest struct. */ + if (id >= ARRAY_SIZE(cpu->lg->cpus)) + return -EINVAL; + + /* Set up this CPU's id, and pointer back to the lguest struct. */ + cpu->id = id; + cpu->lg = container_of((cpu - id), struct lguest, cpus[0]); + cpu->lg->nr_cpus++; + + /* Each CPU has a timer it can set. */ + init_clockdev(cpu); + + /* + * 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. + */ + cpu->regs_page = get_zeroed_page(GFP_KERNEL); + if (!cpu->regs_page) + return -ENOMEM; + + /* We actually put the registers at the bottom of the page. */ + cpu->regs = (void *)cpu->regs_page + PAGE_SIZE - sizeof(*cpu->regs); + + /* + * Now we initialize the Guest's registers, handing it the start + * address. + */ + lguest_arch_setup_regs(cpu, start_ip); + + /* + * We keep a pointer to the Launcher task (ie. current task) for when + * other Guests want to wake this one (eg. console input). + */ + cpu->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. + */ + cpu->mm = get_task_mm(cpu->tsk); + + /* + * We remember which CPU's pages this Guest used last, for optimization + * when the same Guest runs on the same CPU twice. + */ + cpu->last_pages = NULL; + + /* No error == success. */ + return 0; +} + +/*L:020 + * The initialization write supplies 3 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. + * + * start: The first instruction to execute ("eip" in x86-speak). + */ +static int initialize(struct file *file, const unsigned long __user *input) +{ + /* "struct lguest" contains all we (the Host) know about a Guest. */ + struct lguest *lg; + int err; + unsigned long args[3]; + + /* + * 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; + } + + lg->eventfds = kmalloc(sizeof(*lg->eventfds), GFP_KERNEL); + if (!lg->eventfds) { + err = -ENOMEM; + goto free_lg; + } + lg->eventfds->num = 0; + + /* Populate the easy fields of our "struct lguest" */ + lg->mem_base = (void __user *)args[0]; + lg->pfn_limit = args[1]; + + /* This is the first cpu (cpu 0) and it will start booting at args[2] */ + err = lg_cpu_start(&lg->cpus[0], 0, args[2]); + if (err) + goto free_eventfds; + + /* + * Initialize the Guest's shadow page tables. This allocates + * memory, so can fail. + */ + err = init_guest_pagetable(lg); + if (err) + goto free_regs; + + /* 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: + /* FIXME: This should be in free_vcpu */ + free_page(lg->cpus[0].regs_page); +free_eventfds: + kfree(lg->eventfds); +free_lg: + 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 or set up receipt of notifications. + * + * Note that we overload the "offset" in the /dev/lguest file to indicate what + * CPU number we're dealing with. Currently this is always 0 since we only + * support uniprocessor Guests, but you can see the beginnings of SMP support + * here. + */ +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; + struct lg_cpu *uninitialized_var(cpu); + unsigned int cpu_id = *off; + + /* The first value tells us what this request is. */ + if (get_user(req, input) != 0) + return -EFAULT; + input++; + + /* If you haven't initialized, you must do that first. */ + if (req != LHREQ_INITIALIZE) { + if (!lg || (cpu_id >= lg->nr_cpus)) + return -EINVAL; + cpu = &lg->cpus[cpu_id]; + + /* Once the Guest is dead, you can only read() why it died. */ + if (lg->dead) + return -ENOENT; + } + + switch (req) { + case LHREQ_INITIALIZE: + return initialize(file, input); + case LHREQ_IRQ: + return user_send_irq(cpu, input); + case LHREQ_EVENTFD: + return attach_eventfd(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; + unsigned int i; + + /* 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); + + /* Free up the shadow page tables for the Guest. */ + free_guest_pagetable(lg); + + for (i = 0; i < lg->nr_cpus; i++) { + /* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */ + hrtimer_cancel(&lg->cpus[i].hrt); + /* We can free up the register page we allocated. */ + free_page(lg->cpus[i].regs_page); + /* + * Now all the memory cleanups are done, it's safe to release + * the Launcher's memory management structure. + */ + mmput(lg->cpus[i].mm); + } + + /* Release any eventfds they registered. */ + for (i = 0; i < lg->eventfds->num; i++) + eventfd_ctx_put(lg->eventfds->map[i].event); + kfree(lg->eventfds); + + /* + * 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); + /* Free the memory allocated to the lguest_struct */ + kfree(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 const struct file_operations lguest_fops = { + .owner = THIS_MODULE, + .release = close, + .write = write, + .read = read, + .llseek = default_llseek, +}; +/*:*/ + +/* + * 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); +} |