drivers/lguest/core.c - arm/linux - Git at Google

 /*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/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 <asm/uaccess.h>
 #include <asm/poll.h>
 #include <asm/asm-offsets.h>
 #include "lg.h"


 static struct vm_struct *switcher_vma;
 static struct page **switcher_page;

 /* 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;
 	struct page **pagep;

 	/*
 	 * 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 allocate an array of struct page pointers.  map_vm_area() wants
 	 * this, rather than just an array of pages.
 	 */
 	switcher_page = kmalloc(sizeof(switcher_page[0])*TOTAL_SWITCHER_PAGES,
 				GFP_KERNEL);
 	if (!switcher_page) {
 		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++) {
 		switcher_page[i] = alloc_page(GFP_KERNEL|__GFP_ZERO);
 		if (!switcher_page[i]) {
 			err = -ENOMEM;
 			goto free_some_pages;
 		}
 	}

 	/*
 	 * First we check that the Switcher won't overlap the fixmap area at
 	 * the top of memory.  It's currently nowhere near, but it could have
 	 * very strange effects if it ever happened.
 	 */
 	if (SWITCHER_ADDR + (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE > FIXADDR_START){
 		err = -ENOMEM;
 		printk("lguest: mapping switcher would thwack fixmap\n");
 		goto free_pages;
 	}

 	/*
 	 * Now we reserve the "virtual memory area" we want: 0xFFC00000
 	 * (SWITCHER_ADDR).  We might not get it in theory, but in practice
 	 * it's worked so far.  The end address needs +1 because __get_vm_area
 	 * allocates an extra guard page, so we need space for that.
 	 */
 	switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
 				     VM_ALLOC, SWITCHER_ADDR, SWITCHER_ADDR
 				     + (TOTAL_SWITCHER_PAGES+1) * PAGE_SIZE);
 	if (!switcher_vma) {
 		err = -ENOMEM;
 		printk("lguest: could not map switcher pages high\n");
 		goto free_pages;
 	}

 	/*
 	 * 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 pages), and a pointer to our
 	 * array of struct pages.  It increments that pointer, but we don't
 	 * care.
 	 */
 	pagep = switcher_page;
 	err = map_vm_area(switcher_vma, PAGE_KERNEL_EXEC, &pagep);
 	if (err) {
 		printk("lguest: map_vm_area failed: %i\n", err);
 		goto free_vma;
 	}

 	/*
 	 * Now the Switcher is mapped at the right address, we can't fail!
 	 * Copy in the compiled-in Switcher code (from <arch>_switcher.S).
 	 */
 	memcpy(switcher_vma->addr, start_switcher_text,
 	       end_switcher_text - start_switcher_text);

 	printk(KERN_INFO "lguest: mapped switcher at %p\n",
 	       switcher_vma->addr);
 	/* And we succeeded... */
 	return 0;

 free_vma:
 	vunmap(switcher_vma->addr);
 free_pages:
 	i = TOTAL_SWITCHER_PAGES;
 free_some_pages:
 	for (--i; i >= 0; i--)
 		__free_pages(switcher_page[i], 0);
 	kfree(switcher_page);
 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_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(switcher_page[i], 0);
 	kfree(switcher_page);
 }

 /*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) / PAGE_SIZE < lg->pfn_limit && (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)
 {
 	/* 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);

 		/*
 		 * It's possible the Guest did a NOTIFY hypercall to the
 		 * Launcher.
 		 */
 		if (cpu->pending_notify) {
 			/*
 			 * Does it just needs to write to a registered
 			 * eventfd (ie. the appropriate virtqueue thread)?
 			 */
 			if (!send_notify_to_eventfd(cpu)) {
 				/* OK, we tell the main Laucher. */
 				if (put_user(cpu->pending_notify, user))
 					return -EFAULT;
 				return sizeof(cpu->pending_notify);
 			}
 		}

 		/* 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);

 		/*
 		 * 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();

 		/*
 		 * 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 (paravirt_enabled()) {
 		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;

 	/* Now we set up the pagetable implementation for the Guests. */
 	err = init_pagetables(switcher_page, SHARED_SWITCHER_PAGES);
 	if (err)
 		goto unmap;

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

 	/* /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();
 free_pgtables:
 	free_pagetables();
 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();
 	free_pagetables();
 	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/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 <asm/uaccess.h>
	#include <asm/poll.h>
	#include <asm/asm-offsets.h>
	#include "lg.h"


	static struct vm_struct *switcher_vma;
	static struct page **switcher_page;

	/* 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;
	struct page **pagep;

	/*
	* 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 allocate an array of struct page pointers. map_vm_area() wants
	* this, rather than just an array of pages.
	*/
	switcher_page = kmalloc(sizeof(switcher_page[0])*TOTAL_SWITCHER_PAGES,
	GFP_KERNEL);
	if (!switcher_page) {
	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++) {
	switcher_page[i] = alloc_page(GFP_KERNEL\|__GFP_ZERO);
	if (!switcher_page[i]) {
	err = -ENOMEM;
	goto free_some_pages;
	}
	}

	/*
	* First we check that the Switcher won't overlap the fixmap area at
	* the top of memory. It's currently nowhere near, but it could have
	* very strange effects if it ever happened.
	*/
	if (SWITCHER_ADDR + (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE > FIXADDR_START){
	err = -ENOMEM;
	printk("lguest: mapping switcher would thwack fixmap\n");
	goto free_pages;
	}

	/*
	* Now we reserve the "virtual memory area" we want: 0xFFC00000
	* (SWITCHER_ADDR). We might not get it in theory, but in practice
	* it's worked so far. The end address needs +1 because __get_vm_area
	* allocates an extra guard page, so we need space for that.
	*/
	switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
	VM_ALLOC, SWITCHER_ADDR, SWITCHER_ADDR
	+ (TOTAL_SWITCHER_PAGES+1) * PAGE_SIZE);
	if (!switcher_vma) {
	err = -ENOMEM;
	printk("lguest: could not map switcher pages high\n");
	goto free_pages;
	}

	/*
	* 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 pages), and a pointer to our
	* array of struct pages. It increments that pointer, but we don't
	* care.
	*/
	pagep = switcher_page;
	err = map_vm_area(switcher_vma, PAGE_KERNEL_EXEC, &pagep);
	if (err) {
	printk("lguest: map_vm_area failed: %i\n", err);
	goto free_vma;
	}

	/*
	* Now the Switcher is mapped at the right address, we can't fail!
	* Copy in the compiled-in Switcher code (from <arch>_switcher.S).
	*/
	memcpy(switcher_vma->addr, start_switcher_text,
	end_switcher_text - start_switcher_text);

	printk(KERN_INFO "lguest: mapped switcher at %p\n",
	switcher_vma->addr);
	/* And we succeeded... */
	return 0;

	free_vma:
	vunmap(switcher_vma->addr);
	free_pages:
	i = TOTAL_SWITCHER_PAGES;
	free_some_pages:
	for (--i; i >= 0; i--)
	__free_pages(switcher_page[i], 0);
	kfree(switcher_page);
	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_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(switcher_page[i], 0);
	kfree(switcher_page);
	}

	/*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) / PAGE_SIZE < lg->pfn_limit && (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)
	{
	/* 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);

	/*
	* It's possible the Guest did a NOTIFY hypercall to the
	* Launcher.
	*/
	if (cpu->pending_notify) {
	/*
	* Does it just needs to write to a registered
	* eventfd (ie. the appropriate virtqueue thread)?
	*/
	if (!send_notify_to_eventfd(cpu)) {
	/* OK, we tell the main Laucher. */
	if (put_user(cpu->pending_notify, user))
	return -EFAULT;
	return sizeof(cpu->pending_notify);
	}
	}

	/* 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);

	/*
	* 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();

	/*
	* 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 (paravirt_enabled()) {
	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;

	/* Now we set up the pagetable implementation for the Guests. */
	err = init_pagetables(switcher_page, SHARED_SWITCHER_PAGES);
	if (err)
	goto unmap;

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

	/* /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();
	free_pgtables:
	free_pagetables();
	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();
	free_pagetables();
	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>");