linux/drivers/lguest/page_tables.c
Rusty Russell f938d2c892 lguest: documentation I: Preparation
The netfilter code had very good documentation: the Netfilter Hacking HOWTO.
Noone ever read it.

So this time I'm trying something different, using a bit of Knuthiness.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-07-26 11:35:16 -07:00

418 lines
11 KiB
C

/*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"
#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();
}