-/* Userspace control of the guest, via /dev/lguest. */
+/*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"
-static void setup_regs(struct lguest_regs *regs, unsigned long start)
-{
- /* Write out stack in format lguest expects, so we can switch to it. */
- regs->ds = regs->es = regs->ss = __KERNEL_DS|GUEST_PL;
- regs->cs = __KERNEL_CS|GUEST_PL;
- regs->eflags = 0x202; /* Interrupts enabled. */
- regs->eip = start;
- /* esi points to our boot information (physical address 0) */
-}
-
-/* + addr */
-static long user_get_dma(struct lguest *lg, const u32 __user *input)
-{
- unsigned long key, udma, irq;
-
- if (get_user(key, input) != 0)
- return -EFAULT;
- udma = get_dma_buffer(lg, key, &irq);
- if (!udma)
- return -ENOENT;
-
- /* We put irq number in udma->used_len. */
- lgwrite_u32(lg, udma + offsetof(struct lguest_dma, used_len), irq);
- return udma;
-}
-
-/* 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)
+/*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.. */
+ /* 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) */
+ /* 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);
}
}
-/* + irq */
-static int user_send_irq(struct lguest *lg, const u32 __user *input)
+/*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)
{
- u32 irq;
+ 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 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 (lg->dma_is_pending)
- lg->dma_is_pending = 0;
+ /* 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);
}
-/* Take: pfnlimit, pgdir, start, pageoffset. */
-static int initialize(struct file *file, const u32 __user *input)
+/*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, i;
- u32 args[4];
+ int err;
+ unsigned long args[4];
- /* We grab the Big Lguest lock, which protects the global array
- * "lguests" and multiple simultaneous initializations. */
+ /* 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;
goto unlock;
}
- i = find_free_guest();
- if (i < 0) {
- err = -ENOSPC;
+ lg = kzalloc(sizeof(*lg), GFP_KERNEL);
+ if (!lg) {
+ err = -ENOMEM;
goto unlock;
}
- lg = &lguests[i];
- lg->guestid = i;
- lg->pfn_limit = args[0];
- lg->page_offset = args[3];
+
+ /* 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);
- err = init_guest_pagetable(lg, args[1]);
+ /* 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;
- setup_regs(lg->regs, args[2]);
- setup_guest_gdt(lg);
+ /* 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:
return err;
}
-static ssize_t write(struct file *file, const char __user *input,
+/*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;
- u32 req;
+ const unsigned long __user *input = (const unsigned long __user *)in;
+ unsigned long req;
if (get_user(req, input) != 0)
return -EFAULT;
- input += sizeof(req);
+ 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;
switch (req) {
case LHREQ_INITIALIZE:
- return initialize(file, (const u32 __user *)input);
- case LHREQ_GETDMA:
- return user_get_dma(lg, (const u32 __user *)input);
+ return initialize(file, input);
case LHREQ_IRQ:
- return user_send_irq(lg, (const u32 __user *)input);
+ return user_send_irq(lg, input);
case LHREQ_BREAK:
- return break_guest_out(lg, (const u32 __user *)input);
+ 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);
- release_all_dma(lg);
+ /* 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",
git.samba.org / sfrench / cifs-2.6.git / blobdiff