drivers/lguest/core.c - kernel/msm-5.4 - Gitiles

 /*P:400
  * This contains run_guest() which actually calls into the Host<->Guest
  * Switcher and analyzes the return, such as determining if the Guest wants the
  * Host to do something.  This file also contains useful helper routines.
 :*/
 #include <linux/module.h>
 #include <linux/stringify.h>
 #include <linux/stddef.h>
 #include <linux/io.h>
 #include <linux/mm.h>
 #include <linux/sched/signal.h>
 #include <linux/vmalloc.h>
 #include <linux/cpu.h>
 #include <linux/freezer.h>
 #include <linux/highmem.h>
 #include <linux/slab.h>
 #include <asm/paravirt.h>
 #include <asm/pgtable.h>
 #include <linux/uaccess.h>
 #include <asm/poll.h>
 #include <asm/asm-offsets.h>
 #include "lg.h"

 unsigned long switcher_addr;
 struct page **lg_switcher_pages;
 static struct vm_struct *switcher_text_vma;
 static struct vm_struct *switcher_stacks_vma;

 /* This One Big lock protects all inter-guest data structures. */
 DEFINE_MUTEX(lguest_lock);

 /*H:010
  * We need to set up the Switcher at a high virtual address.  Remember the
  * Switcher is a few hundred bytes of assembler code which actually changes the
  * CPU to run the Guest, and then changes back to the Host when a trap or
  * interrupt happens.
  *
  * The Switcher code must be at the same virtual address in the Guest as the
  * Host since it will be running as the switchover occurs.
  *
  * Trying to map memory at a particular address is an unusual thing to do, so
  * it's not a simple one-liner.
  */
 static __init int map_switcher(void)
 {
 	int i, err;

 	/*
 	 * Map the Switcher in to high memory.
 	 *
 	 * It turns out that if we choose the address 0xFFC00000 (4MB under the
 	 * top virtual address), it makes setting up the page tables really
 	 * easy.
 	 */

 	/* We assume Switcher text fits into a single page. */
 	if (end_switcher_text - start_switcher_text > PAGE_SIZE) {
 		printk(KERN_ERR "lguest: switcher text too large (%zu)\n",
 		       end_switcher_text - start_switcher_text);
 		return -EINVAL;
 	}

 	/*
 	 * We allocate an array of struct page pointers.  map_vm_area() wants
 	 * this, rather than just an array of pages.
 	 */
 	lg_switcher_pages = kmalloc(sizeof(lg_switcher_pages[0])
 				    * TOTAL_SWITCHER_PAGES,
 				    GFP_KERNEL);
 	if (!lg_switcher_pages) {
 		err = -ENOMEM;
 		goto out;
 	}

 	/*
 	 * Now we actually allocate the pages.  The Guest will see these pages,
 	 * so we make sure they're zeroed.
 	 */
 	for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
 		lg_switcher_pages[i] = alloc_page(GFP_KERNEL|__GFP_ZERO);
 		if (!lg_switcher_pages[i]) {
 			err = -ENOMEM;
 			goto free_some_pages;
 		}
 	}

 	/*
 	 * Copy in the compiled-in Switcher code (from x86/switcher_32.S).
 	 * It goes in the first page, which we map in momentarily.
 	 */
 	memcpy(kmap(lg_switcher_pages[0]), start_switcher_text,
 	       end_switcher_text - start_switcher_text);
 	kunmap(lg_switcher_pages[0]);

 	/*
 	 * We place the Switcher underneath the fixmap area, which is the
 	 * highest virtual address we can get.  This is important, since we
 	 * tell the Guest it can't access this memory, so we want its ceiling
 	 * as high as possible.
 	 */
 	switcher_addr = FIXADDR_START - TOTAL_SWITCHER_PAGES*PAGE_SIZE;

 	/*
 	 * Now we reserve the "virtual memory area"s we want.  We might
 	 * not get them in theory, but in practice it's worked so far.
 	 *
 	 * We want the switcher text to be read-only and executable, and
 	 * the stacks to be read-write and non-executable.
 	 */
 	switcher_text_vma = __get_vm_area(PAGE_SIZE, VM_ALLOC|VM_NO_GUARD,
 					  switcher_addr,
 					  switcher_addr + PAGE_SIZE);

 	if (!switcher_text_vma) {
 		err = -ENOMEM;
 		printk("lguest: could not map switcher pages high\n");
 		goto free_pages;
 	}

 	switcher_stacks_vma = __get_vm_area(SWITCHER_STACK_PAGES * PAGE_SIZE,
 					    VM_ALLOC|VM_NO_GUARD,
 					    switcher_addr + PAGE_SIZE,
 					    switcher_addr + TOTAL_SWITCHER_PAGES * PAGE_SIZE);
 	if (!switcher_stacks_vma) {
 		err = -ENOMEM;
 		printk("lguest: could not map switcher pages high\n");
 		goto free_text_vma;
 	}

 	/*
 	 * This code actually sets up the pages we've allocated to appear at
 	 * switcher_addr.  map_vm_area() takes the vma we allocated above, the
 	 * kind of pages we're mapping (kernel text pages and kernel writable
 	 * pages respectively), and a pointer to our array of struct pages.
 	 */
 	err = map_vm_area(switcher_text_vma, PAGE_KERNEL_RX, lg_switcher_pages);
 	if (err) {
 		printk("lguest: text map_vm_area failed: %i\n", err);
 		goto free_vmas;
 	}

 	err = map_vm_area(switcher_stacks_vma, PAGE_KERNEL,
 			  lg_switcher_pages + SWITCHER_TEXT_PAGES);
 	if (err) {
 		printk("lguest: stacks map_vm_area failed: %i\n", err);
 		goto free_vmas;
 	}

 	/*
 	 * Now the Switcher is mapped at the right address, we can't fail!
 	 */
 	printk(KERN_INFO "lguest: mapped switcher at %p\n",
 	       switcher_text_vma->addr);
 	/* And we succeeded... */
 	return 0;

 free_vmas:
 	/* Undoes map_vm_area and __get_vm_area */
 	vunmap(switcher_stacks_vma->addr);
 free_text_vma:
 	vunmap(switcher_text_vma->addr);
 free_pages:
 	i = TOTAL_SWITCHER_PAGES;
 free_some_pages:
 	for (--i; i >= 0; i--)
 		__free_pages(lg_switcher_pages[i], 0);
 	kfree(lg_switcher_pages);
 out:
 	return err;
 }
 /*:*/

 /* Cleaning up the mapping when the module is unloaded is almost... too easy. */
 static void unmap_switcher(void)
 {
 	unsigned int i;

 	/* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */
 	vunmap(switcher_text_vma->addr);
 	vunmap(switcher_stacks_vma->addr);
 	/* Now we just need to free the pages we copied the switcher into */
 	for (i = 0; i < TOTAL_SWITCHER_PAGES; i++)
 		__free_pages(lg_switcher_pages[i], 0);
 	kfree(lg_switcher_pages);
 }

 /*H:032
  * Dealing With Guest Memory.
  *
  * Before we go too much further into the Host, we need to grok the routines
  * we use to deal with Guest memory.
  *
  * When the Guest gives us (what it thinks is) a physical address, we can use
  * the normal copy_from_user() & copy_to_user() on the corresponding place in
  * the memory region allocated by the Launcher.
  *
  * But we can't trust the Guest: it might be trying to access the Launcher
  * code.  We have to check that the range is below the pfn_limit the Launcher
  * gave us.  We have to make sure that addr + len doesn't give us a false
  * positive by overflowing, too.
  */
 bool lguest_address_ok(const struct lguest *lg,
 		       unsigned long addr, unsigned long len)
 {
 	return addr+len <= lg->pfn_limit * PAGE_SIZE && (addr+len >= addr);
 }

 /*
  * This routine copies memory from the Guest.  Here we can see how useful the
  * kill_lguest() routine we met in the Launcher can be: we return a random
  * value (all zeroes) instead of needing to return an error.
  */
 void __lgread(struct lg_cpu *cpu, void *b, unsigned long addr, unsigned bytes)
 {
 	if (!lguest_address_ok(cpu->lg, addr, bytes)
 	    || copy_from_user(b, cpu->lg->mem_base + addr, bytes) != 0) {
 		/* copy_from_user should do this, but as we rely on it... */
 		memset(b, 0, bytes);
 		kill_guest(cpu, "bad read address %#lx len %u", addr, bytes);
 	}
 }

 /* This is the write (copy into Guest) version. */
 void __lgwrite(struct lg_cpu *cpu, unsigned long addr, const void *b,
 	       unsigned bytes)
 {
 	if (!lguest_address_ok(cpu->lg, addr, bytes)
 	    || copy_to_user(cpu->lg->mem_base + addr, b, bytes) != 0)
 		kill_guest(cpu, "bad write address %#lx len %u", addr, bytes);
 }
 /*:*/

 /*H:030
  * Let's jump straight to the the main loop which runs the Guest.
  * Remember, this is called by the Launcher reading /dev/lguest, and we keep
  * going around and around until something interesting happens.
  */
 int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
 {
 	/* If the launcher asked for a register with LHREQ_GETREG */
 	if (cpu->reg_read) {
 		if (put_user(*cpu->reg_read, user))
 			return -EFAULT;
 		cpu->reg_read = NULL;
 		return sizeof(*cpu->reg_read);
 	}

 	/* We stop running once the Guest is dead. */
 	while (!cpu->lg->dead) {
 		unsigned int irq;
 		bool more;

 		/* First we run any hypercalls the Guest wants done. */
 		if (cpu->hcall)
 			do_hypercalls(cpu);

 		/* Do we have to tell the Launcher about a trap? */
 		if (cpu->pending.trap) {
 			if (copy_to_user(user, &cpu->pending,
 					 sizeof(cpu->pending)))
 				return -EFAULT;
 			return sizeof(cpu->pending);
 		}

 		/*
 		 * All long-lived kernel loops need to check with this horrible
 		 * thing called the freezer.  If the Host is trying to suspend,
 		 * it stops us.
 		 */
 		try_to_freeze();

 		/* Check for signals */
 		if (signal_pending(current))
 			return -ERESTARTSYS;

 		/*
 		 * Check if there are any interrupts which can be delivered now:
 		 * if so, this sets up the hander to be executed when we next
 		 * run the Guest.
 		 */
 		irq = interrupt_pending(cpu, &more);
 		if (irq < LGUEST_IRQS)
 			try_deliver_interrupt(cpu, irq, more);

 		/*
 		 * Just make absolutely sure the Guest is still alive.  One of
 		 * those hypercalls could have been fatal, for example.
 		 */
 		if (cpu->lg->dead)
 			break;

 		/*
 		 * If the Guest asked to be stopped, we sleep.  The Guest's
 		 * clock timer will wake us.
 		 */
 		if (cpu->halted) {
 			set_current_state(TASK_INTERRUPTIBLE);
 			/*
 			 * Just before we sleep, make sure no interrupt snuck in
 			 * which we should be doing.
 			 */
 			if (interrupt_pending(cpu, &more) < LGUEST_IRQS)
 				set_current_state(TASK_RUNNING);
 			else
 				schedule();
 			continue;
 		}

 		/*
 		 * OK, now we're ready to jump into the Guest.  First we put up
 		 * the "Do Not Disturb" sign:
 		 */
 		local_irq_disable();

 		/* Actually run the Guest until something happens. */
 		lguest_arch_run_guest(cpu);

 		/* Now we're ready to be interrupted or moved to other CPUs */
 		local_irq_enable();

 		/* Now we deal with whatever happened to the Guest. */
 		lguest_arch_handle_trap(cpu);
 	}

 	/* Special case: Guest is 'dead' but wants a reboot. */
 	if (cpu->lg->dead == ERR_PTR(-ERESTART))
 		return -ERESTART;

 	/* The Guest is dead => "No such file or directory" */
 	return -ENOENT;
 }

 /*H:000
  * Welcome to the Host!
  *
  * By this point your brain has been tickled by the Guest code and numbed by
  * the Launcher code; prepare for it to be stretched by the Host code.  This is
  * the heart.  Let's begin at the initialization routine for the Host's lg
  * module.
  */
 static int __init init(void)
 {
 	int err;

 	/* Lguest can't run under Xen, VMI or itself.  It does Tricky Stuff. */
 	if (get_kernel_rpl() != 0) {
 		printk("lguest is afraid of being a guest\n");
 		return -EPERM;
 	}

 	/* First we put the Switcher up in very high virtual memory. */
 	err = map_switcher();
 	if (err)
 		goto out;

 	/* We might need to reserve an interrupt vector. */
 	err = init_interrupts();
 	if (err)
 		goto unmap;

 	/* /dev/lguest needs to be registered. */
 	err = lguest_device_init();
 	if (err)
 		goto free_interrupts;

 	/* Finally we do some architecture-specific setup. */
 	lguest_arch_host_init();

 	/* All good! */
 	return 0;

 free_interrupts:
 	free_interrupts();
 unmap:
 	unmap_switcher();
 out:
 	return err;
 }

 /* Cleaning up is just the same code, backwards.  With a little French. */
 static void __exit fini(void)
 {
 	lguest_device_remove();
 	free_interrupts();
 	unmap_switcher();

 	lguest_arch_host_fini();
 }
 /*:*/

 /*
  * The Host side of lguest can be a module.  This is a nice way for people to
  * play with it.
  */
 module_init(init);
 module_exit(fini);
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
	/*P:400
	* This contains run_guest() which actually calls into the Host<->Guest
	* Switcher and analyzes the return, such as determining if the Guest wants the
	* Host to do something. This file also contains useful helper routines.
	:*/
	#include <linux/module.h>
	#include <linux/stringify.h>
	#include <linux/stddef.h>
	#include <linux/io.h>
	#include <linux/mm.h>
	#include <linux/sched/signal.h>
	#include <linux/vmalloc.h>
	#include <linux/cpu.h>
	#include <linux/freezer.h>
	#include <linux/highmem.h>
	#include <linux/slab.h>
	#include <asm/paravirt.h>
	#include <asm/pgtable.h>
	#include <linux/uaccess.h>
	#include <asm/poll.h>
	#include <asm/asm-offsets.h>
	#include "lg.h"

	unsigned long switcher_addr;
	struct page **lg_switcher_pages;
	static struct vm_struct *switcher_text_vma;
	static struct vm_struct *switcher_stacks_vma;

	/* This One Big lock protects all inter-guest data structures. */
	DEFINE_MUTEX(lguest_lock);

	/*H:010
	* We need to set up the Switcher at a high virtual address. Remember the
	* Switcher is a few hundred bytes of assembler code which actually changes the
	* CPU to run the Guest, and then changes back to the Host when a trap or
	* interrupt happens.
	*
	* The Switcher code must be at the same virtual address in the Guest as the
	* Host since it will be running as the switchover occurs.
	*
	* Trying to map memory at a particular address is an unusual thing to do, so
	* it's not a simple one-liner.
	*/
	static __init int map_switcher(void)
	{
	int i, err;

	/*
	* Map the Switcher in to high memory.
	*
	* It turns out that if we choose the address 0xFFC00000 (4MB under the
	* top virtual address), it makes setting up the page tables really
	* easy.
	*/

	/* We assume Switcher text fits into a single page. */
	if (end_switcher_text - start_switcher_text > PAGE_SIZE) {
	printk(KERN_ERR "lguest: switcher text too large (%zu)\n",
	end_switcher_text - start_switcher_text);
	return -EINVAL;
	}

	/*
	* We allocate an array of struct page pointers. map_vm_area() wants
	* this, rather than just an array of pages.
	*/
	lg_switcher_pages = kmalloc(sizeof(lg_switcher_pages[0])
	* TOTAL_SWITCHER_PAGES,
	GFP_KERNEL);
	if (!lg_switcher_pages) {
	err = -ENOMEM;
	goto out;
	}

	/*
	* Now we actually allocate the pages. The Guest will see these pages,
	* so we make sure they're zeroed.
	*/
	for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
	lg_switcher_pages[i] = alloc_page(GFP_KERNEL\|__GFP_ZERO);
	if (!lg_switcher_pages[i]) {
	err = -ENOMEM;
	goto free_some_pages;
	}
	}

	/*
	* Copy in the compiled-in Switcher code (from x86/switcher_32.S).
	* It goes in the first page, which we map in momentarily.
	*/
	memcpy(kmap(lg_switcher_pages[0]), start_switcher_text,
	end_switcher_text - start_switcher_text);
	kunmap(lg_switcher_pages[0]);

	/*
	* We place the Switcher underneath the fixmap area, which is the
	* highest virtual address we can get. This is important, since we
	* tell the Guest it can't access this memory, so we want its ceiling
	* as high as possible.
	*/
	switcher_addr = FIXADDR_START - TOTAL_SWITCHER_PAGES*PAGE_SIZE;

	/*
	* Now we reserve the "virtual memory area"s we want. We might
	* not get them in theory, but in practice it's worked so far.
	*
	* We want the switcher text to be read-only and executable, and
	* the stacks to be read-write and non-executable.
	*/
	switcher_text_vma = __get_vm_area(PAGE_SIZE, VM_ALLOC\|VM_NO_GUARD,
	switcher_addr,
	switcher_addr + PAGE_SIZE);

	if (!switcher_text_vma) {
	err = -ENOMEM;
	printk("lguest: could not map switcher pages high\n");
	goto free_pages;
	}

	switcher_stacks_vma = __get_vm_area(SWITCHER_STACK_PAGES * PAGE_SIZE,
	VM_ALLOC\|VM_NO_GUARD,
	switcher_addr + PAGE_SIZE,
	switcher_addr + TOTAL_SWITCHER_PAGES * PAGE_SIZE);
	if (!switcher_stacks_vma) {
	err = -ENOMEM;
	printk("lguest: could not map switcher pages high\n");
	goto free_text_vma;
	}

	/*
	* This code actually sets up the pages we've allocated to appear at
	* switcher_addr. map_vm_area() takes the vma we allocated above, the
	* kind of pages we're mapping (kernel text pages and kernel writable
	* pages respectively), and a pointer to our array of struct pages.
	*/
	err = map_vm_area(switcher_text_vma, PAGE_KERNEL_RX, lg_switcher_pages);
	if (err) {
	printk("lguest: text map_vm_area failed: %i\n", err);
	goto free_vmas;
	}

	err = map_vm_area(switcher_stacks_vma, PAGE_KERNEL,
	lg_switcher_pages + SWITCHER_TEXT_PAGES);
	if (err) {
	printk("lguest: stacks map_vm_area failed: %i\n", err);
	goto free_vmas;
	}

	/*
	* Now the Switcher is mapped at the right address, we can't fail!
	*/
	printk(KERN_INFO "lguest: mapped switcher at %p\n",
	switcher_text_vma->addr);
	/* And we succeeded... */
	return 0;

	free_vmas:
	/* Undoes map_vm_area and __get_vm_area */
	vunmap(switcher_stacks_vma->addr);
	free_text_vma:
	vunmap(switcher_text_vma->addr);
	free_pages:
	i = TOTAL_SWITCHER_PAGES;
	free_some_pages:
	for (--i; i >= 0; i--)
	__free_pages(lg_switcher_pages[i], 0);
	kfree(lg_switcher_pages);
	out:
	return err;
	}
	/:/

	/* Cleaning up the mapping when the module is unloaded is almost... too easy. */
	static void unmap_switcher(void)
	{
	unsigned int i;

	/* vunmap() undoes both map_vm_area() and __get_vm_area(). */
	vunmap(switcher_text_vma->addr);
	vunmap(switcher_stacks_vma->addr);
	/* Now we just need to free the pages we copied the switcher into */
	for (i = 0; i < TOTAL_SWITCHER_PAGES; i++)
	__free_pages(lg_switcher_pages[i], 0);
	kfree(lg_switcher_pages);
	}

	/*H:032
	* Dealing With Guest Memory.
	*
	* Before we go too much further into the Host, we need to grok the routines
	* we use to deal with Guest memory.
	*
	* When the Guest gives us (what it thinks is) a physical address, we can use
	* the normal copy_from_user() & copy_to_user() on the corresponding place in
	* the memory region allocated by the Launcher.
	*
	* But we can't trust the Guest: it might be trying to access the Launcher
	* code. We have to check that the range is below the pfn_limit the Launcher
	* gave us. We have to make sure that addr + len doesn't give us a false
	* positive by overflowing, too.
	*/
	bool lguest_address_ok(const struct lguest *lg,
	unsigned long addr, unsigned long len)
	{
	return addr+len <= lg->pfn_limit * PAGE_SIZE && (addr+len >= addr);
	}

	/*
	* This routine copies memory from the Guest. Here we can see how useful the
	* kill_lguest() routine we met in the Launcher can be: we return a random
	* value (all zeroes) instead of needing to return an error.
	*/
	void __lgread(struct lg_cpu cpu, void b, unsigned long addr, unsigned bytes)
	{
	if (!lguest_address_ok(cpu->lg, addr, bytes)
	\|\| copy_from_user(b, cpu->lg->mem_base + addr, bytes) != 0) {
	/* copy_from_user should do this, but as we rely on it... */
	memset(b, 0, bytes);
	kill_guest(cpu, "bad read address %#lx len %u", addr, bytes);
	}
	}

	/* This is the write (copy into Guest) version. */
	void __lgwrite(struct lg_cpu cpu, unsigned long addr, const void b,
	unsigned bytes)
	{
	if (!lguest_address_ok(cpu->lg, addr, bytes)
	\|\| copy_to_user(cpu->lg->mem_base + addr, b, bytes) != 0)
	kill_guest(cpu, "bad write address %#lx len %u", addr, bytes);
	}
	/:/

	/*H:030
	* Let's jump straight to the the main loop which runs the Guest.
	* Remember, this is called by the Launcher reading /dev/lguest, and we keep
	* going around and around until something interesting happens.
	*/
	int run_guest(struct lg_cpu cpu, unsigned long __user user)
	{
	/* If the launcher asked for a register with LHREQ_GETREG */
	if (cpu->reg_read) {
	if (put_user(*cpu->reg_read, user))
	return -EFAULT;
	cpu->reg_read = NULL;
	return sizeof(*cpu->reg_read);
	}

	/* We stop running once the Guest is dead. */
	while (!cpu->lg->dead) {
	unsigned int irq;
	bool more;

	/* First we run any hypercalls the Guest wants done. */
	if (cpu->hcall)
	do_hypercalls(cpu);

	/* Do we have to tell the Launcher about a trap? */
	if (cpu->pending.trap) {
	if (copy_to_user(user, &cpu->pending,
	sizeof(cpu->pending)))
	return -EFAULT;
	return sizeof(cpu->pending);
	}

	/*
	* All long-lived kernel loops need to check with this horrible
	* thing called the freezer. If the Host is trying to suspend,
	* it stops us.
	*/
	try_to_freeze();

	/* Check for signals */
	if (signal_pending(current))
	return -ERESTARTSYS;

	/*
	* Check if there are any interrupts which can be delivered now:
	* if so, this sets up the hander to be executed when we next
	* run the Guest.
	*/
	irq = interrupt_pending(cpu, &more);
	if (irq < LGUEST_IRQS)
	try_deliver_interrupt(cpu, irq, more);

	/*
	* Just make absolutely sure the Guest is still alive. One of
	* those hypercalls could have been fatal, for example.
	*/
	if (cpu->lg->dead)
	break;

	/*
	* If the Guest asked to be stopped, we sleep. The Guest's
	* clock timer will wake us.
	*/
	if (cpu->halted) {
	set_current_state(TASK_INTERRUPTIBLE);
	/*
	* Just before we sleep, make sure no interrupt snuck in
	* which we should be doing.
	*/
	if (interrupt_pending(cpu, &more) < LGUEST_IRQS)
	set_current_state(TASK_RUNNING);
	else
	schedule();
	continue;
	}

	/*
	* OK, now we're ready to jump into the Guest. First we put up
	* the "Do Not Disturb" sign:
	*/
	local_irq_disable();

	/* Actually run the Guest until something happens. */
	lguest_arch_run_guest(cpu);

	/* Now we're ready to be interrupted or moved to other CPUs */
	local_irq_enable();

	/* Now we deal with whatever happened to the Guest. */
	lguest_arch_handle_trap(cpu);
	}

	/* Special case: Guest is 'dead' but wants a reboot. */
	if (cpu->lg->dead == ERR_PTR(-ERESTART))
	return -ERESTART;

	/* The Guest is dead => "No such file or directory" */
	return -ENOENT;
	}

	/*H:000
	* Welcome to the Host!
	*
	* By this point your brain has been tickled by the Guest code and numbed by
	* the Launcher code; prepare for it to be stretched by the Host code. This is
	* the heart. Let's begin at the initialization routine for the Host's lg
	* module.
	*/
	static int __init init(void)
	{
	int err;

	/* Lguest can't run under Xen, VMI or itself. It does Tricky Stuff. */
	if (get_kernel_rpl() != 0) {
	printk("lguest is afraid of being a guest\n");
	return -EPERM;
	}

	/* First we put the Switcher up in very high virtual memory. */
	err = map_switcher();
	if (err)
	goto out;

	/* We might need to reserve an interrupt vector. */
	err = init_interrupts();
	if (err)
	goto unmap;

	/* /dev/lguest needs to be registered. */
	err = lguest_device_init();
	if (err)
	goto free_interrupts;

	/* Finally we do some architecture-specific setup. */
	lguest_arch_host_init();

	/* All good! */
	return 0;

	free_interrupts:
	free_interrupts();
	unmap:
	unmap_switcher();
	out:
	return err;
	}

	/* Cleaning up is just the same code, backwards. With a little French. */
	static void __exit fini(void)
	{
	lguest_device_remove();
	free_interrupts();
	unmap_switcher();

	lguest_arch_host_fini();
	}
	/:/

	/*
	* The Host side of lguest can be a module. This is a nice way for people to
	* play with it.
	*/
	module_init(init);
	module_exit(fini);
	MODULE_LICENSE("GPL");
	MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");