-/* 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 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)
{
- /* Write out stack in format lguest expects, so we can switch to it. */
+ /* 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;
- regs->eflags = 0x202; /* Interrupts enabled. */
+
+ /* 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 (physical address 0) */
+
+ /* %esi points to our boot information, at physical address 0, so don't
+ * touch it. */
}
-/* + addr */
+/*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 put irq number in udma->used_len. */
+ /* 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;
}
-/* To force the Guest to stop running and return to the Launcher, the
+/*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)
}
}
-/* + irq */
+/*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;
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 (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);
}
-/* Take: pfnlimit, pgdir, start, pageoffset. */
+/*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. */
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;
}
+ /* 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. */
setup_guest_gdt(lg);
+
+ /* 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;
}
+/*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;
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;
}
}
+/*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 any DMA buffers the Guest had bound. */
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. 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 = {
.minor = MISC_DYNAMIC_MINOR,
.name = "lguest",
projects / linux-2.6-omap-h63xx.git / blobdiff