drivers/lguest/page_tables.c - linux - Git at Google

 /* Shadow page table operations.
  * Copyright (C) Rusty Russell IBM Corporation 2006.
  * GPL v2 and any later version */
 #include <linux/mm.h>
 #include <linux/types.h>
 #include <linux/spinlock.h>
 #include <linux/random.h>
 #include <linux/percpu.h>
 #include <asm/tlbflush.h>
 #include "lg.h"

 #define PTES_PER_PAGE_SHIFT 10
 #define PTES_PER_PAGE (1 << PTES_PER_PAGE_SHIFT)
 #define SWITCHER_PGD_INDEX (PTES_PER_PAGE - 1)

 static DEFINE_PER_CPU(spte_t *, switcher_pte_pages);
 #define switcher_pte_page(cpu) per_cpu(switcher_pte_pages, cpu)

 static unsigned vaddr_to_pgd_index(unsigned long vaddr)
 {
 	return vaddr >> (PAGE_SHIFT + PTES_PER_PAGE_SHIFT);
 }

 /* These access the shadow versions (ie. the ones used by the CPU). */
 static spgd_t *spgd_addr(struct lguest *lg, u32 i, unsigned long vaddr)
 {
 	unsigned int index = vaddr_to_pgd_index(vaddr);

 	if (index >= SWITCHER_PGD_INDEX) {
 		kill_guest(lg, "attempt to access switcher pages");
 		index = 0;
 	}
 	return &lg->pgdirs[i].pgdir[index];
 }

 static spte_t *spte_addr(struct lguest *lg, spgd_t spgd, unsigned long vaddr)
 {
 	spte_t *page = __va(spgd.pfn << PAGE_SHIFT);
 	BUG_ON(!(spgd.flags & _PAGE_PRESENT));
 	return &page[(vaddr >> PAGE_SHIFT) % PTES_PER_PAGE];
 }

 /* These access the guest versions. */
 static unsigned long gpgd_addr(struct lguest *lg, unsigned long vaddr)
 {
 	unsigned int index = vaddr >> (PAGE_SHIFT + PTES_PER_PAGE_SHIFT);
 	return lg->pgdirs[lg->pgdidx].cr3 + index * sizeof(gpgd_t);
 }

 static unsigned long gpte_addr(struct lguest *lg,
 			       gpgd_t gpgd, unsigned long vaddr)
 {
 	unsigned long gpage = gpgd.pfn << PAGE_SHIFT;
 	BUG_ON(!(gpgd.flags & _PAGE_PRESENT));
 	return gpage + ((vaddr>>PAGE_SHIFT) % PTES_PER_PAGE) * sizeof(gpte_t);
 }

 /* Do a virtual -> physical mapping on a user page. */
 static unsigned long get_pfn(unsigned long virtpfn, int write)
 {
 	struct page *page;
 	unsigned long ret = -1UL;

 	down_read(&current->mm->mmap_sem);
 	if (get_user_pages(current, current->mm, virtpfn << PAGE_SHIFT,
 			   1, write, 1, &page, NULL) == 1)
 		ret = page_to_pfn(page);
 	up_read(&current->mm->mmap_sem);
 	return ret;
 }

 static spte_t gpte_to_spte(struct lguest *lg, gpte_t gpte, int write)
 {
 	spte_t spte;
 	unsigned long pfn;

 	/* We ignore the global flag. */
 	spte.flags = (gpte.flags & ~_PAGE_GLOBAL);
 	pfn = get_pfn(gpte.pfn, write);
 	if (pfn == -1UL) {
 		kill_guest(lg, "failed to get page %u", gpte.pfn);
 		/* Must not put_page() bogus page on cleanup. */
 		spte.flags = 0;
 	}
 	spte.pfn = pfn;
 	return spte;
 }

 static void release_pte(spte_t pte)
 {
 	if (pte.flags & _PAGE_PRESENT)
 		put_page(pfn_to_page(pte.pfn));
 }

 static void check_gpte(struct lguest *lg, gpte_t gpte)
 {
 	if ((gpte.flags & (_PAGE_PWT|_PAGE_PSE)) || gpte.pfn >= lg->pfn_limit)
 		kill_guest(lg, "bad page table entry");
 }

 static void check_gpgd(struct lguest *lg, gpgd_t gpgd)
 {
 	if ((gpgd.flags & ~_PAGE_TABLE) || gpgd.pfn >= lg->pfn_limit)
 		kill_guest(lg, "bad page directory entry");
 }

 /* FIXME: We hold reference to pages, which prevents them from being
    swapped.  It'd be nice to have a callback when Linux wants to swap out. */

 /* We fault pages in, which allows us to update accessed/dirty bits.
  * Return true if we got page. */
 int demand_page(struct lguest *lg, unsigned long vaddr, int errcode)
 {
 	gpgd_t gpgd;
 	spgd_t *spgd;
 	unsigned long gpte_ptr;
 	gpte_t gpte;
 	spte_t *spte;

 	gpgd = mkgpgd(lgread_u32(lg, gpgd_addr(lg, vaddr)));
 	if (!(gpgd.flags & _PAGE_PRESENT))
 		return 0;

 	spgd = spgd_addr(lg, lg->pgdidx, vaddr);
 	if (!(spgd->flags & _PAGE_PRESENT)) {
 		/* Get a page of PTEs for them. */
 		unsigned long ptepage = get_zeroed_page(GFP_KERNEL);
 		/* FIXME: Steal from self in this case? */
 		if (!ptepage) {
 			kill_guest(lg, "out of memory allocating pte page");
 			return 0;
 		}
 		check_gpgd(lg, gpgd);
 		spgd->raw.val = (__pa(ptepage) | gpgd.flags);
 	}

 	gpte_ptr = gpte_addr(lg, gpgd, vaddr);
 	gpte = mkgpte(lgread_u32(lg, gpte_ptr));

 	/* No page? */
 	if (!(gpte.flags & _PAGE_PRESENT))
 		return 0;

 	/* Write to read-only page? */
 	if ((errcode & 2) && !(gpte.flags & _PAGE_RW))
 		return 0;

 	/* User access to a non-user page? */
 	if ((errcode & 4) && !(gpte.flags & _PAGE_USER))
 		return 0;

 	check_gpte(lg, gpte);
 	gpte.flags |= _PAGE_ACCESSED;
 	if (errcode & 2)
 		gpte.flags |= _PAGE_DIRTY;

 	/* We're done with the old pte. */
 	spte = spte_addr(lg, *spgd, vaddr);
 	release_pte(*spte);

 	/* We don't make it writable if this isn't a write: later
 	 * write will fault so we can set dirty bit in guest. */
 	if (gpte.flags & _PAGE_DIRTY)
 		*spte = gpte_to_spte(lg, gpte, 1);
 	else {
 		gpte_t ro_gpte = gpte;
 		ro_gpte.flags &= ~_PAGE_RW;
 		*spte = gpte_to_spte(lg, ro_gpte, 0);
 	}

 	/* Now we update dirty/accessed on guest. */
 	lgwrite_u32(lg, gpte_ptr, gpte.raw.val);
 	return 1;
 }

 /* This is much faster than the full demand_page logic. */
 static int page_writable(struct lguest *lg, unsigned long vaddr)
 {
 	spgd_t *spgd;
 	unsigned long flags;

 	spgd = spgd_addr(lg, lg->pgdidx, vaddr);
 	if (!(spgd->flags & _PAGE_PRESENT))
 		return 0;

 	flags = spte_addr(lg, *spgd, vaddr)->flags;
 	return (flags & (_PAGE_PRESENT|_PAGE_RW)) == (_PAGE_PRESENT|_PAGE_RW);
 }

 void pin_page(struct lguest *lg, unsigned long vaddr)
 {
 	if (!page_writable(lg, vaddr) && !demand_page(lg, vaddr, 2))
 		kill_guest(lg, "bad stack page %#lx", vaddr);
 }

 static void release_pgd(struct lguest *lg, spgd_t *spgd)
 {
 	if (spgd->flags & _PAGE_PRESENT) {
 		unsigned int i;
 		spte_t *ptepage = __va(spgd->pfn << PAGE_SHIFT);
 		for (i = 0; i < PTES_PER_PAGE; i++)
 			release_pte(ptepage[i]);
 		free_page((long)ptepage);
 		spgd->raw.val = 0;
 	}
 }

 static void flush_user_mappings(struct lguest *lg, int idx)
 {
 	unsigned int i;
 	for (i = 0; i < vaddr_to_pgd_index(lg->page_offset); i++)
 		release_pgd(lg, lg->pgdirs[idx].pgdir + i);
 }

 void guest_pagetable_flush_user(struct lguest *lg)
 {
 	flush_user_mappings(lg, lg->pgdidx);
 }

 static unsigned int find_pgdir(struct lguest *lg, unsigned long pgtable)
 {
 	unsigned int i;
 	for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
 		if (lg->pgdirs[i].cr3 == pgtable)
 			break;
 	return i;
 }

 static unsigned int new_pgdir(struct lguest *lg,
 			      unsigned long cr3,
 			      int *blank_pgdir)
 {
 	unsigned int next;

 	next = random32() % ARRAY_SIZE(lg->pgdirs);
 	if (!lg->pgdirs[next].pgdir) {
 		lg->pgdirs[next].pgdir = (spgd_t *)get_zeroed_page(GFP_KERNEL);
 		if (!lg->pgdirs[next].pgdir)
 			next = lg->pgdidx;
 		else
 			/* There are no mappings: you'll need to re-pin */
 			*blank_pgdir = 1;
 	}
 	lg->pgdirs[next].cr3 = cr3;
 	/* Release all the non-kernel mappings. */
 	flush_user_mappings(lg, next);

 	return next;
 }

 void guest_new_pagetable(struct lguest *lg, unsigned long pgtable)
 {
 	int newpgdir, repin = 0;

 	newpgdir = find_pgdir(lg, pgtable);
 	if (newpgdir == ARRAY_SIZE(lg->pgdirs))
 		newpgdir = new_pgdir(lg, pgtable, &repin);
 	lg->pgdidx = newpgdir;
 	if (repin)
 		pin_stack_pages(lg);
 }

 static void release_all_pagetables(struct lguest *lg)
 {
 	unsigned int i, j;

 	for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
 		if (lg->pgdirs[i].pgdir)
 			for (j = 0; j < SWITCHER_PGD_INDEX; j++)
 				release_pgd(lg, lg->pgdirs[i].pgdir + j);
 }

 void guest_pagetable_clear_all(struct lguest *lg)
 {
 	release_all_pagetables(lg);
 	pin_stack_pages(lg);
 }

 static void do_set_pte(struct lguest *lg, int idx,
 		       unsigned long vaddr, gpte_t gpte)
 {
 	spgd_t *spgd = spgd_addr(lg, idx, vaddr);
 	if (spgd->flags & _PAGE_PRESENT) {
 		spte_t *spte = spte_addr(lg, *spgd, vaddr);
 		release_pte(*spte);
 		if (gpte.flags & (_PAGE_DIRTY | _PAGE_ACCESSED)) {
 			check_gpte(lg, gpte);
 			*spte = gpte_to_spte(lg, gpte, gpte.flags&_PAGE_DIRTY);
 		} else
 			spte->raw.val = 0;
 	}
 }

 void guest_set_pte(struct lguest *lg,
 		   unsigned long cr3, unsigned long vaddr, gpte_t gpte)
 {
 	/* Kernel mappings must be changed on all top levels. */
 	if (vaddr >= lg->page_offset) {
 		unsigned int i;
 		for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
 			if (lg->pgdirs[i].pgdir)
 				do_set_pte(lg, i, vaddr, gpte);
 	} else {
 		int pgdir = find_pgdir(lg, cr3);
 		if (pgdir != ARRAY_SIZE(lg->pgdirs))
 			do_set_pte(lg, pgdir, vaddr, gpte);
 	}
 }

 void guest_set_pmd(struct lguest *lg, unsigned long cr3, u32 idx)
 {
 	int pgdir;

 	if (idx >= SWITCHER_PGD_INDEX)
 		return;

 	pgdir = find_pgdir(lg, cr3);
 	if (pgdir < ARRAY_SIZE(lg->pgdirs))
 		release_pgd(lg, lg->pgdirs[pgdir].pgdir + idx);
 }

 int init_guest_pagetable(struct lguest *lg, unsigned long pgtable)
 {
 	/* We assume this in flush_user_mappings, so check now */
 	if (vaddr_to_pgd_index(lg->page_offset) >= SWITCHER_PGD_INDEX)
 		return -EINVAL;
 	lg->pgdidx = 0;
 	lg->pgdirs[lg->pgdidx].cr3 = pgtable;
 	lg->pgdirs[lg->pgdidx].pgdir = (spgd_t*)get_zeroed_page(GFP_KERNEL);
 	if (!lg->pgdirs[lg->pgdidx].pgdir)
 		return -ENOMEM;
 	return 0;
 }

 void free_guest_pagetable(struct lguest *lg)
 {
 	unsigned int i;

 	release_all_pagetables(lg);
 	for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
 		free_page((long)lg->pgdirs[i].pgdir);
 }

 /* Caller must be preempt-safe */
 void map_switcher_in_guest(struct lguest *lg, struct lguest_pages *pages)
 {
 	spte_t *switcher_pte_page = __get_cpu_var(switcher_pte_pages);
 	spgd_t switcher_pgd;
 	spte_t regs_pte;

 	/* Since switcher less that 4MB, we simply mug top pte page. */
 	switcher_pgd.pfn = __pa(switcher_pte_page) >> PAGE_SHIFT;
 	switcher_pgd.flags = _PAGE_KERNEL;
 	lg->pgdirs[lg->pgdidx].pgdir[SWITCHER_PGD_INDEX] = switcher_pgd;

 	/* Map our regs page over stack page. */
 	regs_pte.pfn = __pa(lg->regs_page) >> PAGE_SHIFT;
 	regs_pte.flags = _PAGE_KERNEL;
 	switcher_pte_page[(unsigned long)pages/PAGE_SIZE%PTES_PER_PAGE]
 		= regs_pte;
 }

 static void free_switcher_pte_pages(void)
 {
 	unsigned int i;

 	for_each_possible_cpu(i)
 		free_page((long)switcher_pte_page(i));
 }

 static __init void populate_switcher_pte_page(unsigned int cpu,
 					      struct page *switcher_page[],
 					      unsigned int pages)
 {
 	unsigned int i;
 	spte_t *pte = switcher_pte_page(cpu);

 	for (i = 0; i < pages; i++) {
 		pte[i].pfn = page_to_pfn(switcher_page[i]);
 		pte[i].flags = _PAGE_PRESENT|_PAGE_ACCESSED;
 	}

 	/* We only map this CPU's pages, so guest can't see others. */
 	i = pages + cpu*2;

 	/* First page (regs) is rw, second (state) is ro. */
 	pte[i].pfn = page_to_pfn(switcher_page[i]);
 	pte[i].flags = _PAGE_PRESENT|_PAGE_ACCESSED|_PAGE_RW;
 	pte[i+1].pfn = page_to_pfn(switcher_page[i+1]);
 	pte[i+1].flags = _PAGE_PRESENT|_PAGE_ACCESSED;
 }

 __init int init_pagetables(struct page **switcher_page, unsigned int pages)
 {
 	unsigned int i;

 	for_each_possible_cpu(i) {
 		switcher_pte_page(i) = (spte_t *)get_zeroed_page(GFP_KERNEL);
 		if (!switcher_pte_page(i)) {
 			free_switcher_pte_pages();
 			return -ENOMEM;
 		}
 		populate_switcher_pte_page(i, switcher_page, pages);
 	}
 	return 0;
 }

 void free_pagetables(void)
 {
 	free_switcher_pte_pages();
 }
	/* Shadow page table operations.
	* Copyright (C) Rusty Russell IBM Corporation 2006.
	* GPL v2 and any later version */
	#include <linux/mm.h>
	#include <linux/types.h>
	#include <linux/spinlock.h>
	#include <linux/random.h>
	#include <linux/percpu.h>
	#include <asm/tlbflush.h>
	#include "lg.h"

	#define PTES_PER_PAGE_SHIFT 10
	#define PTES_PER_PAGE (1 << PTES_PER_PAGE_SHIFT)
	#define SWITCHER_PGD_INDEX (PTES_PER_PAGE - 1)

	static DEFINE_PER_CPU(spte_t *, switcher_pte_pages);
	#define switcher_pte_page(cpu) per_cpu(switcher_pte_pages, cpu)

	static unsigned vaddr_to_pgd_index(unsigned long vaddr)
	{
	return vaddr >> (PAGE_SHIFT + PTES_PER_PAGE_SHIFT);
	}

	/* These access the shadow versions (ie. the ones used by the CPU). */
	static spgd_t spgd_addr(struct lguest lg, u32 i, unsigned long vaddr)
	{
	unsigned int index = vaddr_to_pgd_index(vaddr);

	if (index >= SWITCHER_PGD_INDEX) {
	kill_guest(lg, "attempt to access switcher pages");
	index = 0;
	}
	return &lg->pgdirs[i].pgdir[index];
	}

	static spte_t spte_addr(struct lguest lg, spgd_t spgd, unsigned long vaddr)
	{
	spte_t *page = __va(spgd.pfn << PAGE_SHIFT);
	BUG_ON(!(spgd.flags & _PAGE_PRESENT));
	return &page[(vaddr >> PAGE_SHIFT) % PTES_PER_PAGE];
	}

	/* These access the guest versions. */
	static unsigned long gpgd_addr(struct lguest *lg, unsigned long vaddr)
	{
	unsigned int index = vaddr >> (PAGE_SHIFT + PTES_PER_PAGE_SHIFT);
	return lg->pgdirs[lg->pgdidx].cr3 + index * sizeof(gpgd_t);
	}

	static unsigned long gpte_addr(struct lguest *lg,
	gpgd_t gpgd, unsigned long vaddr)
	{
	unsigned long gpage = gpgd.pfn << PAGE_SHIFT;
	BUG_ON(!(gpgd.flags & _PAGE_PRESENT));
	return gpage + ((vaddr>>PAGE_SHIFT) % PTES_PER_PAGE) * sizeof(gpte_t);
	}

	/* Do a virtual -> physical mapping on a user page. */
	static unsigned long get_pfn(unsigned long virtpfn, int write)
	{
	struct page *page;
	unsigned long ret = -1UL;

	down_read(&current->mm->mmap_sem);
	if (get_user_pages(current, current->mm, virtpfn << PAGE_SHIFT,
	1, write, 1, &page, NULL) == 1)
	ret = page_to_pfn(page);
	up_read(&current->mm->mmap_sem);
	return ret;
	}

	static spte_t gpte_to_spte(struct lguest *lg, gpte_t gpte, int write)
	{
	spte_t spte;
	unsigned long pfn;

	/* We ignore the global flag. */
	spte.flags = (gpte.flags & ~_PAGE_GLOBAL);
	pfn = get_pfn(gpte.pfn, write);
	if (pfn == -1UL) {
	kill_guest(lg, "failed to get page %u", gpte.pfn);
	/* Must not put_page() bogus page on cleanup. */
	spte.flags = 0;
	}
	spte.pfn = pfn;
	return spte;
	}

	static void release_pte(spte_t pte)
	{
	if (pte.flags & _PAGE_PRESENT)
	put_page(pfn_to_page(pte.pfn));
	}

	static void check_gpte(struct lguest *lg, gpte_t gpte)
	{
	if ((gpte.flags & (_PAGE_PWT\|_PAGE_PSE)) \|\| gpte.pfn >= lg->pfn_limit)
	kill_guest(lg, "bad page table entry");
	}

	static void check_gpgd(struct lguest *lg, gpgd_t gpgd)
	{
	if ((gpgd.flags & ~_PAGE_TABLE) \|\| gpgd.pfn >= lg->pfn_limit)
	kill_guest(lg, "bad page directory entry");
	}

	/* FIXME: We hold reference to pages, which prevents them from being
	swapped. It'd be nice to have a callback when Linux wants to swap out. */

	/* We fault pages in, which allows us to update accessed/dirty bits.
	* Return true if we got page. */
	int demand_page(struct lguest *lg, unsigned long vaddr, int errcode)
	{
	gpgd_t gpgd;
	spgd_t *spgd;
	unsigned long gpte_ptr;
	gpte_t gpte;
	spte_t *spte;

	gpgd = mkgpgd(lgread_u32(lg, gpgd_addr(lg, vaddr)));
	if (!(gpgd.flags & _PAGE_PRESENT))
	return 0;

	spgd = spgd_addr(lg, lg->pgdidx, vaddr);
	if (!(spgd->flags & _PAGE_PRESENT)) {
	/* Get a page of PTEs for them. */
	unsigned long ptepage = get_zeroed_page(GFP_KERNEL);
	/* FIXME: Steal from self in this case? */
	if (!ptepage) {
	kill_guest(lg, "out of memory allocating pte page");
	return 0;
	}
	check_gpgd(lg, gpgd);
	spgd->raw.val = (__pa(ptepage) \| gpgd.flags);
	}

	gpte_ptr = gpte_addr(lg, gpgd, vaddr);
	gpte = mkgpte(lgread_u32(lg, gpte_ptr));

	/* No page? */
	if (!(gpte.flags & _PAGE_PRESENT))
	return 0;

	/* Write to read-only page? */
	if ((errcode & 2) && !(gpte.flags & _PAGE_RW))
	return 0;

	/* User access to a non-user page? */
	if ((errcode & 4) && !(gpte.flags & _PAGE_USER))
	return 0;

	check_gpte(lg, gpte);
	gpte.flags \|= _PAGE_ACCESSED;
	if (errcode & 2)
	gpte.flags \|= _PAGE_DIRTY;

	/* We're done with the old pte. */
	spte = spte_addr(lg, *spgd, vaddr);
	release_pte(*spte);

	/* We don't make it writable if this isn't a write: later
	* write will fault so we can set dirty bit in guest. */
	if (gpte.flags & _PAGE_DIRTY)
	*spte = gpte_to_spte(lg, gpte, 1);
	else {
	gpte_t ro_gpte = gpte;
	ro_gpte.flags &= ~_PAGE_RW;
	*spte = gpte_to_spte(lg, ro_gpte, 0);
	}

	/* Now we update dirty/accessed on guest. */
	lgwrite_u32(lg, gpte_ptr, gpte.raw.val);
	return 1;
	}

	/* This is much faster than the full demand_page logic. */
	static int page_writable(struct lguest *lg, unsigned long vaddr)
	{
	spgd_t *spgd;
	unsigned long flags;

	spgd = spgd_addr(lg, lg->pgdidx, vaddr);
	if (!(spgd->flags & _PAGE_PRESENT))
	return 0;

	flags = spte_addr(lg, *spgd, vaddr)->flags;
	return (flags & (_PAGE_PRESENT\|_PAGE_RW)) == (_PAGE_PRESENT\|_PAGE_RW);
	}

	void pin_page(struct lguest *lg, unsigned long vaddr)
	{
	if (!page_writable(lg, vaddr) && !demand_page(lg, vaddr, 2))
	kill_guest(lg, "bad stack page %#lx", vaddr);
	}

	static void release_pgd(struct lguest lg, spgd_t spgd)
	{
	if (spgd->flags & _PAGE_PRESENT) {
	unsigned int i;
	spte_t *ptepage = __va(spgd->pfn << PAGE_SHIFT);
	for (i = 0; i < PTES_PER_PAGE; i++)
	release_pte(ptepage[i]);
	free_page((long)ptepage);
	spgd->raw.val = 0;
	}
	}

	static void flush_user_mappings(struct lguest *lg, int idx)
	{
	unsigned int i;
	for (i = 0; i < vaddr_to_pgd_index(lg->page_offset); i++)
	release_pgd(lg, lg->pgdirs[idx].pgdir + i);
	}

	void guest_pagetable_flush_user(struct lguest *lg)
	{
	flush_user_mappings(lg, lg->pgdidx);
	}

	static unsigned int find_pgdir(struct lguest *lg, unsigned long pgtable)
	{
	unsigned int i;
	for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
	if (lg->pgdirs[i].cr3 == pgtable)
	break;
	return i;
	}

	static unsigned int new_pgdir(struct lguest *lg,
	unsigned long cr3,
	int *blank_pgdir)
	{
	unsigned int next;

	next = random32() % ARRAY_SIZE(lg->pgdirs);
	if (!lg->pgdirs[next].pgdir) {
	lg->pgdirs[next].pgdir = (spgd_t *)get_zeroed_page(GFP_KERNEL);
	if (!lg->pgdirs[next].pgdir)
	next = lg->pgdidx;
	else
	/* There are no mappings: you'll need to re-pin */
	*blank_pgdir = 1;
	}
	lg->pgdirs[next].cr3 = cr3;
	/* Release all the non-kernel mappings. */
	flush_user_mappings(lg, next);

	return next;
	}

	void guest_new_pagetable(struct lguest *lg, unsigned long pgtable)
	{
	int newpgdir, repin = 0;

	newpgdir = find_pgdir(lg, pgtable);
	if (newpgdir == ARRAY_SIZE(lg->pgdirs))
	newpgdir = new_pgdir(lg, pgtable, &repin);
	lg->pgdidx = newpgdir;
	if (repin)
	pin_stack_pages(lg);
	}

	static void release_all_pagetables(struct lguest *lg)
	{
	unsigned int i, j;

	for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
	if (lg->pgdirs[i].pgdir)
	for (j = 0; j < SWITCHER_PGD_INDEX; j++)
	release_pgd(lg, lg->pgdirs[i].pgdir + j);
	}

	void guest_pagetable_clear_all(struct lguest *lg)
	{
	release_all_pagetables(lg);
	pin_stack_pages(lg);
	}

	static void do_set_pte(struct lguest *lg, int idx,
	unsigned long vaddr, gpte_t gpte)
	{
	spgd_t *spgd = spgd_addr(lg, idx, vaddr);
	if (spgd->flags & _PAGE_PRESENT) {
	spte_t spte = spte_addr(lg, spgd, vaddr);
	release_pte(*spte);
	if (gpte.flags & (_PAGE_DIRTY \| _PAGE_ACCESSED)) {
	check_gpte(lg, gpte);
	*spte = gpte_to_spte(lg, gpte, gpte.flags&_PAGE_DIRTY);
	} else
	spte->raw.val = 0;
	}
	}

	void guest_set_pte(struct lguest *lg,
	unsigned long cr3, unsigned long vaddr, gpte_t gpte)
	{
	/* Kernel mappings must be changed on all top levels. */
	if (vaddr >= lg->page_offset) {
	unsigned int i;
	for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
	if (lg->pgdirs[i].pgdir)
	do_set_pte(lg, i, vaddr, gpte);
	} else {
	int pgdir = find_pgdir(lg, cr3);
	if (pgdir != ARRAY_SIZE(lg->pgdirs))
	do_set_pte(lg, pgdir, vaddr, gpte);
	}
	}

	void guest_set_pmd(struct lguest *lg, unsigned long cr3, u32 idx)
	{
	int pgdir;

	if (idx >= SWITCHER_PGD_INDEX)
	return;

	pgdir = find_pgdir(lg, cr3);
	if (pgdir < ARRAY_SIZE(lg->pgdirs))
	release_pgd(lg, lg->pgdirs[pgdir].pgdir + idx);
	}

	int init_guest_pagetable(struct lguest *lg, unsigned long pgtable)
	{
	/* We assume this in flush_user_mappings, so check now */
	if (vaddr_to_pgd_index(lg->page_offset) >= SWITCHER_PGD_INDEX)
	return -EINVAL;
	lg->pgdidx = 0;
	lg->pgdirs[lg->pgdidx].cr3 = pgtable;
	lg->pgdirs[lg->pgdidx].pgdir = (spgd_t*)get_zeroed_page(GFP_KERNEL);
	if (!lg->pgdirs[lg->pgdidx].pgdir)
	return -ENOMEM;
	return 0;
	}

	void free_guest_pagetable(struct lguest *lg)
	{
	unsigned int i;

	release_all_pagetables(lg);
	for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
	free_page((long)lg->pgdirs[i].pgdir);
	}

	/* Caller must be preempt-safe */
	void map_switcher_in_guest(struct lguest lg, struct lguest_pages pages)
	{
	spte_t *switcher_pte_page = __get_cpu_var(switcher_pte_pages);
	spgd_t switcher_pgd;
	spte_t regs_pte;

	/* Since switcher less that 4MB, we simply mug top pte page. */
	switcher_pgd.pfn = __pa(switcher_pte_page) >> PAGE_SHIFT;
	switcher_pgd.flags = _PAGE_KERNEL;
	lg->pgdirs[lg->pgdidx].pgdir[SWITCHER_PGD_INDEX] = switcher_pgd;

	/* Map our regs page over stack page. */
	regs_pte.pfn = __pa(lg->regs_page) >> PAGE_SHIFT;
	regs_pte.flags = _PAGE_KERNEL;
	switcher_pte_page[(unsigned long)pages/PAGE_SIZE%PTES_PER_PAGE]
	= regs_pte;
	}

	static void free_switcher_pte_pages(void)
	{
	unsigned int i;

	for_each_possible_cpu(i)
	free_page((long)switcher_pte_page(i));
	}

	static __init void populate_switcher_pte_page(unsigned int cpu,
	struct page *switcher_page[],
	unsigned int pages)
	{
	unsigned int i;
	spte_t *pte = switcher_pte_page(cpu);

	for (i = 0; i < pages; i++) {
	pte[i].pfn = page_to_pfn(switcher_page[i]);
	pte[i].flags = _PAGE_PRESENT\|_PAGE_ACCESSED;
	}

	/* We only map this CPU's pages, so guest can't see others. */
	i = pages + cpu*2;

	/* First page (regs) is rw, second (state) is ro. */
	pte[i].pfn = page_to_pfn(switcher_page[i]);
	pte[i].flags = _PAGE_PRESENT\|_PAGE_ACCESSED\|_PAGE_RW;
	pte[i+1].pfn = page_to_pfn(switcher_page[i+1]);
	pte[i+1].flags = _PAGE_PRESENT\|_PAGE_ACCESSED;
	}

	__init int init_pagetables(struct page **switcher_page, unsigned int pages)
	{
	unsigned int i;

	for_each_possible_cpu(i) {
	switcher_pte_page(i) = (spte_t *)get_zeroed_page(GFP_KERNEL);
	if (!switcher_pte_page(i)) {
	free_switcher_pte_pages();
	return -ENOMEM;
	}
	populate_switcher_pte_page(i, switcher_page, pages);
	}
	return 0;
	}

	void free_pagetables(void)
	{
	free_switcher_pte_pages();
	}