blob: e73a000473cc524cd16d9773da390047d362751e [file] [log] [blame]
/*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 <linux/sched.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 lg_cpu *cpu, 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) {
cpu->break_out = 1;
/* Pop it out of the Guest (may be running on different CPU) */
/* Wait for them to reset it */
return wait_event_interruptible(cpu->break_wq, !cpu->break_out);
} else {
cpu->break_out = 0;
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 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_bit(irq, cpu->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;
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]);
/* Each CPU has a timer it can set. */
/* 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);
/* Initialize the queue for the Waker to wait on */
/* 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 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. */
/* 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 *)args[0];
lg->pfn_limit = args[1];
/* This is the first cpu (cpu 0) and it will start booting at args[3] */
err = lg_cpu_start(&lg->cpus[0], 0, args[3]);
if (err)
goto release_guest;
/* 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;
/* We keep our "struct lguest" in the file's private_data. */
file->private_data = lg;
/* And because this is a write() call, we return the length used. */
return sizeof(args);
/* FIXME: This should be in free_vcpu */
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.
* 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;
/* 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;
/* If you're not the task which owns the Guest, all you can do
* is break the Launcher out of running the Guest. */
if (current != cpu->tsk && req != LHREQ_BREAK)
return -EPERM;
switch (req) {
return initialize(file, input);
return user_send_irq(cpu, input);
return break_guest_out(cpu, input);
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. */
/* Free up the shadow page tables for the Guest. */
for (i = 0; i < lg->nr_cpus; i++) {
/* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */
/* We can free up the register page we allocated. */
/* Now all the memory cleanups are done, it's safe to release
* the Launcher's memory management structure. */
/* 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))
/* We clear the entire structure, which also marks it as free for the
* next user. */
memset(lg, 0, sizeof(*lg));
/* Release lock and exit. */
return 0;
* 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 = {
.name = "lguest",
.fops = &lguest_fops,
int __init lguest_device_init(void)
return misc_register(&lguest_dev);
void __exit lguest_device_remove(void)