blob: b7a924ace68426d85167adb6121f7e39364e9be4 [file] [log] [blame]
/*P:700 The pagetable code, on the other hand, still shows the scars of
* previous encounters. It's functional, and as neat as it can be in the
* circumstances, but be wary, for these things are subtle and break easily.
* The Guest provides a virtual to physical mapping, but we can neither trust
* it nor use it: we verify and convert it here to point the hardware to the
* actual Guest pages when running the Guest. :*/
/* 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"
/*M:008 We hold reference to pages, which prevents them from being swapped.
* It'd be nice to have a callback in the "struct mm_struct" when Linux wants
* to swap out. If we had this, and a shrinker callback to trim PTE pages, we
* could probably consider launching Guests as non-root. :*/
* The Page Table Code
* We use two-level page tables for the Guest. If you're not entirely
* comfortable with virtual addresses, physical addresses and page tables then
* I recommend you review lguest.c's "Page Table Handling" (with diagrams!).
* The Guest keeps page tables, but we maintain the actual ones here: these are
* called "shadow" page tables. Which is a very Guest-centric name: these are
* the real page tables the CPU uses, although we keep them up to date to
* reflect the Guest's. (See what I mean about weird naming? Since when do
* shadows reflect anything?)
* Anyway, this is the most complicated part of the Host code. There are seven
* parts to this:
* (i) Setting up a page table entry for the Guest when it faults,
* (ii) Setting up the page table entry for the Guest stack,
* (iii) Setting up a page table entry when the Guest tells us it has changed,
* (iv) Switching page tables,
* (v) Flushing (thowing away) page tables,
* (vi) Mapping the Switcher when the Guest is about to run,
* (vii) Setting up the page tables initially.
/* Pages a 4k long, and each page table entry is 4 bytes long, giving us 1024
* (or 2^10) entries per page. */
/* 1024 entries in a page table page maps 1024 pages: 4MB. The Switcher is
* conveniently placed at the top 4MB, so it uses a separate, complete PTE
* page. */
/* We actually need a separate PTE page for each CPU. Remember that after the
* Switcher code itself comes two pages for each CPU, and we don't want this
* CPU's guest to see the pages of any other CPU. */
static DEFINE_PER_CPU(spte_t *, switcher_pte_pages);
#define switcher_pte_page(cpu) per_cpu(switcher_pte_pages, cpu)
/*H:320 With our shadow and Guest types established, we need to deal with
* them: the page table code is curly enough to need helper functions to keep
* it clear and clean.
* The first helper takes a virtual address, and says which entry in the top
* level page table deals with that address. Since each top level entry deals
* with 4M, this effectively divides by 4M. */
static unsigned vaddr_to_pgd_index(unsigned long vaddr)
return vaddr >> (PAGE_SHIFT + PTES_PER_PAGE_SHIFT);
/* There are two functions which return pointers to the shadow (aka "real")
* page tables.
* spgd_addr() takes the virtual address and returns a pointer to the top-level
* page directory entry for that address. Since we keep track of several page
* tables, the "i" argument tells us which one we're interested in (it's
* usually the current one). */
static spgd_t *spgd_addr(struct lguest *lg, u32 i, unsigned long vaddr)
unsigned int index = vaddr_to_pgd_index(vaddr);
/* We kill any Guest trying to touch the Switcher addresses. */
if (index >= SWITCHER_PGD_INDEX) {
kill_guest(lg, "attempt to access switcher pages");
index = 0;
/* Return a pointer index'th pgd entry for the i'th page table. */
return &lg->pgdirs[i].pgdir[index];
/* This routine then takes the PGD entry given above, which contains the
* address of the PTE page. It then returns a pointer to the PTE entry for the
* given address. */
static spte_t *spte_addr(struct lguest *lg, spgd_t spgd, unsigned long vaddr)
spte_t *page = __va(spgd.pfn << PAGE_SHIFT);
/* You should never call this if the PGD entry wasn't valid */
BUG_ON(!(spgd.flags & _PAGE_PRESENT));
return &page[(vaddr >> PAGE_SHIFT) % PTES_PER_PAGE];
/* These two functions just like the above two, except they access the Guest
* page tables. Hence they return a Guest address. */
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);
/*H:350 This routine takes a page number given by the Guest and converts it to
* an actual, physical page number. It can fail for several reasons: the
* virtual address might not be mapped by the Launcher, the write flag is set
* and the page is read-only, or the write flag was set and the page was
* shared so had to be copied, but we ran out of memory.
* This holds a reference to the page, so release_pte() is careful to
* put that back. */
static unsigned long get_pfn(unsigned long virtpfn, int write)
struct page *page;
/* This value indicates failure. */
unsigned long ret = -1UL;
/* get_user_pages() is a complex interface: it gets the "struct
* vm_area_struct" and "struct page" assocated with a range of pages.
* It also needs the task's mmap_sem held, and is not very quick.
* It returns the number of pages it got. */
if (get_user_pages(current, current->mm, virtpfn << PAGE_SHIFT,
1, write, 1, &page, NULL) == 1)
ret = page_to_pfn(page);
return ret;
/*H:340 Converting a Guest page table entry to a shadow (ie. real) page table
* entry can be a little tricky. The flags are (almost) the same, but the
* Guest PTE contains a virtual page number: the CPU needs the real page
* number. */
static spte_t gpte_to_spte(struct lguest *lg, gpte_t gpte, int write)
spte_t spte;
unsigned long pfn;
/* The Guest sets the global flag, because it thinks that it is using
* PGE. We only told it to use PGE so it would tell us whether it was
* flushing a kernel mapping or a userspace mapping. We don't actually
* use the global bit, so throw it away. */
spte.flags = (gpte.flags & ~_PAGE_GLOBAL);
/* We need a temporary "unsigned long" variable to hold the answer from
* get_pfn(), because it returns 0xFFFFFFFF on failure, which wouldn't
* fit in spte.pfn. get_pfn() finds the real physical number of the
* page, given the virtual number. */
pfn = get_pfn(gpte.pfn, write);
if (pfn == -1UL) {
kill_guest(lg, "failed to get page %u", gpte.pfn);
/* When we destroy the Guest, we'll go through the shadow page
* tables and release_pte() them. Make sure we don't think
* this one is valid! */
spte.flags = 0;
/* Now we assign the page number, and our shadow PTE is complete. */
spte.pfn = pfn;
return spte;
/*H:460 And to complete the chain, release_pte() looks like this: */
static void release_pte(spte_t pte)
/* Remember that get_user_pages() took a reference to the page, in
* get_pfn()? We have to put it back now. */
if (pte.flags & _PAGE_PRESENT)
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");
* (i) Setting up a page table entry for the Guest when it faults
* We saw this call in run_guest(): when we see a page fault in the Guest, we
* come here. That's because we only set up the shadow page tables lazily as
* they're needed, so we get page faults all the time and quietly fix them up
* and return to the Guest without it knowing.
* If we fixed up the fault (ie. we mapped the address), this routine returns
* true. */
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;
/* First step: get the top-level Guest page table entry. */
gpgd = mkgpgd(lgread_u32(lg, gpgd_addr(lg, vaddr)));
/* Toplevel not present? We can't map it in. */
if (!(gpgd.flags & _PAGE_PRESENT))
return 0;
/* Now look at the matching shadow entry. */
spgd = spgd_addr(lg, lg->pgdidx, vaddr);
if (!(spgd->flags & _PAGE_PRESENT)) {
/* No shadow entry: allocate a new shadow PTE page. */
unsigned long ptepage = get_zeroed_page(GFP_KERNEL);
/* This is not really the Guest's fault, but killing it is
* simple for this corner case. */
if (!ptepage) {
kill_guest(lg, "out of memory allocating pte page");
return 0;
/* We check that the Guest pgd is OK. */
check_gpgd(lg, gpgd);
/* And we copy the flags to the shadow PGD entry. The page
* number in the shadow PGD is the page we just allocated. */
spgd->raw.val = (__pa(ptepage) | gpgd.flags);
/* OK, now we look at the lower level in the Guest page table: keep its
* address, because we might update it later. */
gpte_ptr = gpte_addr(lg, gpgd, vaddr);
gpte = mkgpte(lgread_u32(lg, gpte_ptr));
/* If this page isn't in the Guest page tables, we can't page it in. */
if (!(gpte.flags & _PAGE_PRESENT))
return 0;
/* Check they're not trying to write to a page the Guest wants
* read-only (bit 2 of errcode == write). */
if ((errcode & 2) && !(gpte.flags & _PAGE_RW))
return 0;
/* User access to a kernel page? (bit 3 == user access) */
if ((errcode & 4) && !(gpte.flags & _PAGE_USER))
return 0;
/* Check that the Guest PTE flags are OK, and the page number is below
* the pfn_limit (ie. not mapping the Launcher binary). */
check_gpte(lg, gpte);
/* Add the _PAGE_ACCESSED and (for a write) _PAGE_DIRTY flag */
gpte.flags |= _PAGE_ACCESSED;
if (errcode & 2)
gpte.flags |= _PAGE_DIRTY;
/* Get the pointer to the shadow PTE entry we're going to set. */
spte = spte_addr(lg, *spgd, vaddr);
/* If there was a valid shadow PTE entry here before, we release it.
* This can happen with a write to a previously read-only entry. */
/* If this is a write, we insist that the Guest page is writable (the
* final arg to gpte_to_spte()). */
if (gpte.flags & _PAGE_DIRTY)
*spte = gpte_to_spte(lg, gpte, 1);
else {
/* If this is a read, don't set the "writable" bit in the page
* table entry, even if the Guest says it's writable. That way
* we come back here when a write does actually ocur, so we can
* update the Guest's _PAGE_DIRTY flag. */
gpte_t ro_gpte = gpte;
ro_gpte.flags &= ~_PAGE_RW;
*spte = gpte_to_spte(lg, ro_gpte, 0);
/* Finally, we write the Guest PTE entry back: we've set the
* _PAGE_ACCESSED and maybe the _PAGE_DIRTY flags. */
lgwrite_u32(lg, gpte_ptr, gpte.raw.val);
/* We succeeded in mapping the page! */
return 1;
/*H:360 (ii) Setting up the page table entry for the Guest stack.
* Remember pin_stack_pages() which makes sure the stack is mapped? It could
* simply call demand_page(), but as we've seen that logic is quite long, and
* usually the stack pages are already mapped anyway, so it's not required.
* This is a quick version which answers the question: is this virtual address
* mapped by the shadow page tables, and is it writable? */
static int page_writable(struct lguest *lg, unsigned long vaddr)
spgd_t *spgd;
unsigned long flags;
/* Look at the top level entry: is it present? */
spgd = spgd_addr(lg, lg->pgdidx, vaddr);
if (!(spgd->flags & _PAGE_PRESENT))
return 0;
/* Check the flags on the pte entry itself: it must be present and
* writable. */
flags = spte_addr(lg, *spgd, vaddr)->flags;
return (flags & (_PAGE_PRESENT|_PAGE_RW)) == (_PAGE_PRESENT|_PAGE_RW);
/* So, when pin_stack_pages() asks us to pin a page, we check if it's already
* in the page tables, and if not, we call demand_page() with error code 2
* (meaning "write"). */
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);
/*H:450 If we chase down the release_pgd() code, it looks like this: */
static void release_pgd(struct lguest *lg, spgd_t *spgd)
/* If the entry's not present, there's nothing to release. */
if (spgd->flags & _PAGE_PRESENT) {
unsigned int i;
/* Converting the pfn to find the actual PTE page is easy: turn
* the page number into a physical address, then convert to a
* virtual address (easy for kernel pages like this one). */
spte_t *ptepage = __va(spgd->pfn << PAGE_SHIFT);
/* For each entry in the page, we might need to release it. */
for (i = 0; i < PTES_PER_PAGE; i++)
/* Now we can free the page of PTEs */
/* And zero out the PGD entry we we never release it twice. */
spgd->raw.val = 0;
/*H:440 (v) Flushing (thowing away) page tables,
* We saw flush_user_mappings() called when we re-used a top-level pgdir page.
* It simply releases every PTE page from 0 up to the kernel address. */
static void flush_user_mappings(struct lguest *lg, int idx)
unsigned int i;
/* Release every pgd entry up to the kernel's address. */
for (i = 0; i < vaddr_to_pgd_index(lg->page_offset); i++)
release_pgd(lg, lg->pgdirs[idx].pgdir + i);
/* The Guest also has a hypercall to do this manually: it's used when a large
* number of mappings have been changed. */
void guest_pagetable_flush_user(struct lguest *lg)
/* Drop the userspace part of the current page table. */
flush_user_mappings(lg, lg->pgdidx);
/* We keep several page tables. This is a simple routine to find the page
* table (if any) corresponding to this top-level address the Guest has given
* us. */
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)
return i;
/*H:435 And this is us, creating the new page directory. If we really do
* allocate a new one (and so the kernel parts are not there), we set
* blank_pgdir. */
static unsigned int new_pgdir(struct lguest *lg,
unsigned long cr3,
int *blank_pgdir)
unsigned int next;
/* We pick one entry at random to throw out. Choosing the Least
* Recently Used might be better, but this is easy. */
next = random32() % ARRAY_SIZE(lg->pgdirs);
/* If it's never been allocated at all before, try now. */
if (!lg->pgdirs[next].pgdir) {
lg->pgdirs[next].pgdir = (spgd_t *)get_zeroed_page(GFP_KERNEL);
/* If the allocation fails, just keep using the one we have */
if (!lg->pgdirs[next].pgdir)
next = lg->pgdidx;
/* This is a blank page, so there are no kernel
* mappings: caller must map the stack! */
*blank_pgdir = 1;
/* Record which Guest toplevel this shadows. */
lg->pgdirs[next].cr3 = cr3;
/* Release all the non-kernel mappings. */
flush_user_mappings(lg, next);
return next;
/*H:430 (iv) Switching page tables
* This is what happens when the Guest changes page tables (ie. changes the
* top-level pgdir). This happens on almost every context switch. */
void guest_new_pagetable(struct lguest *lg, unsigned long pgtable)
int newpgdir, repin = 0;
/* Look to see if we have this one already. */
newpgdir = find_pgdir(lg, pgtable);
/* If not, we allocate or mug an existing one: if it's a fresh one,
* repin gets set to 1. */
if (newpgdir == ARRAY_SIZE(lg->pgdirs))
newpgdir = new_pgdir(lg, pgtable, &repin);
/* Change the current pgd index to the new one. */
lg->pgdidx = newpgdir;
/* If it was completely blank, we map in the Guest kernel stack */
if (repin)
/*H:470 Finally, a routine which throws away everything: all PGD entries in all
* the shadow page tables. This is used when we destroy the Guest. */
static void release_all_pagetables(struct lguest *lg)
unsigned int i, j;
/* Every shadow pagetable this Guest has */
for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
if (lg->pgdirs[i].pgdir)
/* Every PGD entry except the Switcher at the top */
for (j = 0; j < SWITCHER_PGD_INDEX; j++)
release_pgd(lg, lg->pgdirs[i].pgdir + j);
/* We also throw away everything when a Guest tells us it's changed a kernel
* mapping. Since kernel mappings are in every page table, it's easiest to
* throw them all away. This is amazingly slow, but thankfully rare. */
void guest_pagetable_clear_all(struct lguest *lg)
/* We need the Guest kernel stack mapped again. */
/*H:420 This is the routine which actually sets the page table entry for then
* "idx"'th shadow page table.
* Normally, we can just throw out the old entry and replace it with 0: if they
* use it demand_page() will put the new entry in. We need to do this anyway:
* The Guest expects _PAGE_ACCESSED to be set on its PTE the first time a page
* is read from, and _PAGE_DIRTY when it's written to.
* But Avi Kivity pointed out that most Operating Systems (Linux included) set
* these bits on PTEs immediately anyway. This is done to save the CPU from
* having to update them, but it helps us the same way: if they set
* _PAGE_ACCESSED then we can put a read-only PTE entry in immediately, and if
* they set _PAGE_DIRTY then we can put a writable PTE entry in immediately.
static void do_set_pte(struct lguest *lg, int idx,
unsigned long vaddr, gpte_t gpte)
/* Look up the matching shadow page directot entry. */
spgd_t *spgd = spgd_addr(lg, idx, vaddr);
/* If the top level isn't present, there's no entry to update. */
if (spgd->flags & _PAGE_PRESENT) {
/* Otherwise, we start by releasing the existing entry. */
spte_t *spte = spte_addr(lg, *spgd, vaddr);
/* If they're setting this entry as dirty or accessed, we might
* as well put that entry they've given us in now. This shaves
* 10% off a copy-on-write micro-benchmark. */
if (gpte.flags & (_PAGE_DIRTY | _PAGE_ACCESSED)) {
check_gpte(lg, gpte);
*spte = gpte_to_spte(lg, gpte, gpte.flags&_PAGE_DIRTY);
} else
/* Otherwise we can demand_page() it in later. */
spte->raw.val = 0;
/*H:410 Updating a PTE entry is a little trickier.
* We keep track of several different page tables (the Guest uses one for each
* process, so it makes sense to cache at least a few). Each of these have
* identical kernel parts: ie. every mapping above PAGE_OFFSET is the same for
* all processes. So when the page table above that address changes, we update
* all the page tables, not just the current one. This is rare.
* The benefit is that when we have to track a new page table, we can copy keep
* all the kernel mappings. This speeds up context switch immensely. */
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. Slow, but
* doesn't happen often. */
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 {
/* Is this page table one we have a shadow for? */
int pgdir = find_pgdir(lg, cr3);
if (pgdir != ARRAY_SIZE(lg->pgdirs))
/* If so, do the update. */
do_set_pte(lg, pgdir, vaddr, gpte);
* (iii) Setting up a page table entry when the Guest tells us it has changed.
* Just like we did in interrupts_and_traps.c, it makes sense for us to deal
* with the other side of page tables while we're here: what happens when the
* Guest asks for a page table to be updated?
* We already saw that demand_page() will fill in the shadow page tables when
* needed, so we can simply remove shadow page table entries whenever the Guest
* tells us they've changed. When the Guest tries to use the new entry it will
* fault and demand_page() will fix it up.
* So with that in mind here's our code to to update a (top-level) PGD entry:
void guest_set_pmd(struct lguest *lg, unsigned long cr3, u32 idx)
int pgdir;
/* The kernel seems to try to initialize this early on: we ignore its
* attempts to map over the Switcher. */
/* If they're talking about a page table we have a shadow for... */
pgdir = find_pgdir(lg, cr3);
if (pgdir < ARRAY_SIZE(lg->pgdirs))
/* ... throw it away. */
release_pgd(lg, lg->pgdirs[pgdir].pgdir + idx);
/*H:500 (vii) Setting up the page tables initially.
* When a Guest is first created, the Launcher tells us where the toplevel of
* its first page table is. We set some things up here: */
int init_guest_pagetable(struct lguest *lg, unsigned long pgtable)
/* In flush_user_mappings() we loop from 0 to
* "vaddr_to_pgd_index(lg->page_offset)". This assumes it won't hit
* the Switcher mappings, so check that now. */
if (vaddr_to_pgd_index(lg->page_offset) >= SWITCHER_PGD_INDEX)
return -EINVAL;
/* We start on the first shadow page table, and give it a blank PGD
* page. */
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;
/* When a Guest dies, our cleanup is fairly simple. */
void free_guest_pagetable(struct lguest *lg)
unsigned int i;
/* Throw away all page table pages. */
/* Now free the top levels: free_page() can handle 0 just fine. */
for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
/*H:480 (vi) Mapping the Switcher when the Guest is about to run.
* The Switcher and the two pages for this CPU need to be available to the
* Guest (and not the pages for other CPUs). We have the appropriate PTE pages
* for each CPU already set up, we just need to hook them in. */
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;
/* Make the last PGD entry for this Guest point to the Switcher's PTE
* page for this CPU (with appropriate flags). */
switcher_pgd.pfn = __pa(switcher_pte_page) >> PAGE_SHIFT;
switcher_pgd.flags = _PAGE_KERNEL;
lg->pgdirs[lg->pgdidx].pgdir[SWITCHER_PGD_INDEX] = switcher_pgd;
/* We also change the Switcher PTE page. When we're running the Guest,
* we want the Guest's "regs" page to appear where the first Switcher
* page for this CPU is. This is an optimization: when the Switcher
* saves the Guest registers, it saves them into the first page of this
* CPU's "struct lguest_pages": if we make sure the Guest's register
* page is already mapped there, we don't have to copy them out
* again. */
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;
/*H:520 Setting up the Switcher PTE page for given CPU is fairly easy, given
* the CPU number and the "struct page"s for the Switcher code itself.
* Currently the Switcher is less than a page long, so "pages" is always 1. */
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);
/* The first entries are easy: they map the Switcher code. */
for (i = 0; i < pages; i++) {
pte[i].pfn = page_to_pfn(switcher_page[i]);
/* The only other thing we map is this CPU's pair of pages. */
i = pages + cpu*2;
/* First page (Guest registers) is writable from the Guest */
pte[i].pfn = page_to_pfn(switcher_page[i]);
/* The second page contains the "struct lguest_ro_state", and is
* read-only. */
pte[i+1].pfn = page_to_pfn(switcher_page[i+1]);
pte[i+1].flags = _PAGE_PRESENT|_PAGE_ACCESSED;
/*H:510 At boot or module load time, init_pagetables() allocates and populates
* the Switcher PTE page for each CPU. */
__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)) {
return -ENOMEM;
populate_switcher_pte_page(i, switcher_page, pages);
return 0;
/* Cleaning up simply involves freeing the PTE page for each CPU. */
void free_pagetables(void)