blob: 80d1b58c76986b9d245637e4e29999793260ddcd [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 memory size, pagetable, entry point and kernel address offset.
* A read will run the Guest until a signal is pending (-EINTR), or the Guest
* does a DMA out to the Launcher. Writes are also used to get a DMA buffer
* registered by the Guest and to send the Guest an interrupt. :*/
#include <linux/uaccess.h>
#include <linux/miscdevice.h>
#include <linux/fs.h>
#include "lg.h"
/*L:030 setup_regs() doesn't really belong in this file, but it gives us an
* early glimpse deeper into the Host so it's worth having here.
* Most of the Guest's registers are left alone: we used get_zeroed_page() to
* allocate the structure, so they will be 0. */
static void setup_regs(struct lguest_regs *regs, unsigned long start)
/* There are four "segment" registers which the Guest needs to boot:
* The "code segment" register (cs) refers to the kernel code segment
* __KERNEL_CS, and the "data", "extra" and "stack" segment registers
* refer to the kernel data segment __KERNEL_DS.
* The privilege level is packed into the lower bits. The Guest runs
* at privilege level 1 (GUEST_PL).*/
regs->ds = regs->es = regs->ss = __KERNEL_DS|GUEST_PL;
regs->cs = __KERNEL_CS|GUEST_PL;
/* The "eflags" register contains miscellaneous flags. Bit 1 (0x002)
* is supposed to always be "1". Bit 9 (0x200) controls whether
* interrupts are enabled. We always leave interrupts enabled while
* running the Guest. */
regs->eflags = 0x202;
/* The "Extended Instruction Pointer" register says where the Guest is
* running. */
regs->eip = start;
/* %esi points to our boot information, at physical address 0, so don't
* touch it. */
/*L:310 To send DMA into the Guest, the Launcher needs to be able to ask for a
* DMA buffer. This is done by writing LHREQ_GETDMA and the key to
* /dev/lguest. */
static long user_get_dma(struct lguest *lg, const u32 __user *input)
unsigned long key, udma, irq;
/* Fetch the key they wrote to us. */
if (get_user(key, input) != 0)
return -EFAULT;
/* Look for a free Guest DMA buffer bound to that key. */
udma = get_dma_buffer(lg, key, &irq);
if (!udma)
return -ENOENT;
/* We need to tell the Launcher what interrupt the Guest expects after
* the buffer is filled. We stash it in udma->used_len. */
lgwrite_u32(lg, udma + offsetof(struct lguest_dma, used_len), irq);
/* The (guest-physical) address of the DMA buffer is returned from
* the write(). */
return udma;
/*L:315 To force the Guest to stop running and return to the Launcher, the
* Waker sets writes LHREQ_BREAK and the value "1" to /dev/lguest. The
* Launcher then writes LHREQ_BREAK and "0" to release the Waker. */
static int break_guest_out(struct lguest *lg, const u32 __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 (may be running on different CPU) */
/* Wait for them to reset it */
return wait_event_interruptible(lg->break_wq, !lg->break_out);
} else {
lg->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 lguest *lg, const u32 __user *input)
u32 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 sent DMA,
* clear the flag. */
if (lg->dma_is_pending)
lg->dma_is_pending = 0;
/* Run the Guest until something interesting happens. */
return run_guest(lg, (unsigned long __user *)user);
/*L:020 The initialization write supplies 4 32-bit values (in addition to the
* 32-bit LHREQ_INITIALIZE value). These are:
* pfnlimit: The highest (Guest-physical) page number the Guest should be
* allowed to access. The Launcher has to live in Guest memory, so it sets
* this to ensure the Guest can't reach it.
* 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).
* page_offset: The PAGE_OFFSET constant in the Guest kernel. We should
* probably wean the code off this, but it's a very useful constant! Any
* address above this is within the Guest kernel, and any kernel address can
* quickly converted from physical to virtual by adding PAGE_OFFSET. It's
* 0xC0000000 (3G) by default, but it's configurable at kernel build time.
static int initialize(struct file *file, const u32 __user *input)
/* "struct lguest" contains everything we (the Host) know about a
* Guest. */
struct lguest *lg;
int err, i;
u32 args[4];
/* We grab the Big Lguest lock, which protects the global array
* "lguests" and 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;
/* Find an unused guest. */
i = find_free_guest();
if (i < 0) {
err = -ENOSPC;
goto unlock;
/* OK, we have an index into the "lguest" array: "lg" is a convenient
* pointer. */
lg = &lguests[i];
/* Populate the easy fields of our "struct lguest" */
lg->guestid = i;
lg->pfn_limit = args[0];
lg->page_offset = args[3];
/* 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[1]);
if (err)
goto free_regs;
/* Now we initialize the Guest's registers, handing it the start
* address. */
setup_regs(lg->regs, args[2]);
/* There are a couple of GDT entries the Guest expects when first
* booting. */
/* The timer for lguest's clock needs initialization. */
/* 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 */
/* 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;
/* And because this is a write() call, we return the length used. */
return sizeof(args);
memset(lg, 0, sizeof(*lg));
return err;
/*L:010 The first operation the Launcher does must be a write. All writes
* start with a 32 bit 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 get DMA buffers and send interrupts. */
static ssize_t write(struct file *file, const char __user *input,
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;
u32 req;
if (get_user(req, input) != 0)
return -EFAULT;
input += sizeof(req);
/* 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) {
return initialize(file, (const u32 __user *)input);
return user_get_dma(lg, (const u32 __user *)input);
return user_send_irq(lg, (const u32 __user *)input);
return break_guest_out(lg, (const u32 __user *)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;
/* 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. */
/* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */
/* Free any DMA buffers the Guest had bound. */
/* Free up the shadow page tables for the Guest. */
/* 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 can free up the register page we allocated. */
/* 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. The Guest can't tell what's done by the the Launcher and what by
* the Host.
* 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)