linux/drivers/lguest/page_tables.c
Tejun Heo 5a0e3ad6af include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h
percpu.h is included by sched.h and module.h and thus ends up being
included when building most .c files.  percpu.h includes slab.h which
in turn includes gfp.h making everything defined by the two files
universally available and complicating inclusion dependencies.

percpu.h -> slab.h dependency is about to be removed.  Prepare for
this change by updating users of gfp and slab facilities include those
headers directly instead of assuming availability.  As this conversion
needs to touch large number of source files, the following script is
used as the basis of conversion.

  http://userweb.kernel.org/~tj/misc/slabh-sweep.py

The script does the followings.

* Scan files for gfp and slab usages and update includes such that
  only the necessary includes are there.  ie. if only gfp is used,
  gfp.h, if slab is used, slab.h.

* When the script inserts a new include, it looks at the include
  blocks and try to put the new include such that its order conforms
  to its surrounding.  It's put in the include block which contains
  core kernel includes, in the same order that the rest are ordered -
  alphabetical, Christmas tree, rev-Xmas-tree or at the end if there
  doesn't seem to be any matching order.

* If the script can't find a place to put a new include (mostly
  because the file doesn't have fitting include block), it prints out
  an error message indicating which .h file needs to be added to the
  file.

The conversion was done in the following steps.

1. The initial automatic conversion of all .c files updated slightly
   over 4000 files, deleting around 700 includes and adding ~480 gfp.h
   and ~3000 slab.h inclusions.  The script emitted errors for ~400
   files.

2. Each error was manually checked.  Some didn't need the inclusion,
   some needed manual addition while adding it to implementation .h or
   embedding .c file was more appropriate for others.  This step added
   inclusions to around 150 files.

3. The script was run again and the output was compared to the edits
   from #2 to make sure no file was left behind.

4. Several build tests were done and a couple of problems were fixed.
   e.g. lib/decompress_*.c used malloc/free() wrappers around slab
   APIs requiring slab.h to be added manually.

5. The script was run on all .h files but without automatically
   editing them as sprinkling gfp.h and slab.h inclusions around .h
   files could easily lead to inclusion dependency hell.  Most gfp.h
   inclusion directives were ignored as stuff from gfp.h was usually
   wildly available and often used in preprocessor macros.  Each
   slab.h inclusion directive was examined and added manually as
   necessary.

6. percpu.h was updated not to include slab.h.

7. Build test were done on the following configurations and failures
   were fixed.  CONFIG_GCOV_KERNEL was turned off for all tests (as my
   distributed build env didn't work with gcov compiles) and a few
   more options had to be turned off depending on archs to make things
   build (like ipr on powerpc/64 which failed due to missing writeq).

   * x86 and x86_64 UP and SMP allmodconfig and a custom test config.
   * powerpc and powerpc64 SMP allmodconfig
   * sparc and sparc64 SMP allmodconfig
   * ia64 SMP allmodconfig
   * s390 SMP allmodconfig
   * alpha SMP allmodconfig
   * um on x86_64 SMP allmodconfig

8. percpu.h modifications were reverted so that it could be applied as
   a separate patch and serve as bisection point.

Given the fact that I had only a couple of failures from tests on step
6, I'm fairly confident about the coverage of this conversion patch.
If there is a breakage, it's likely to be something in one of the arch
headers which should be easily discoverable easily on most builds of
the specific arch.

Signed-off-by: Tejun Heo <tj@kernel.org>
Guess-its-ok-by: Christoph Lameter <cl@linux-foundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
2010-03-30 22:02:32 +09:00

1263 lines
39 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 then point the CPU to the
* converted 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/gfp.h>
#include <linux/types.h>
#include <linux/spinlock.h>
#include <linux/random.h>
#include <linux/percpu.h>
#include <asm/tlbflush.h>
#include <asm/uaccess.h>
#include <asm/bootparam.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.
:*/
/*H:300
* The Page Table Code
*
* We use two-level page tables for the Guest, or three-level with PAE. If
* you're not entirely comfortable with virtual addresses, physical addresses
* and page tables then I recommend you review arch/x86/lguest/boot.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) Looking up a page table entry when the Guest faults,
* (ii) Making sure the Guest stack is mapped,
* (iii) Setting up a page table entry when the Guest tells us one has changed,
* (iv) Switching page tables,
* (v) Flushing (throwing away) page tables,
* (vi) Mapping the Switcher when the Guest is about to run,
* (vii) Setting up the page tables initially.
:*/
/*
* The Switcher uses the complete top PTE page. That's 1024 PTE entries (4MB)
* or 512 PTE entries with PAE (2MB).
*/
#define SWITCHER_PGD_INDEX (PTRS_PER_PGD - 1)
/*
* For PAE we need the PMD index as well. We use the last 2MB, so we
* will need the last pmd entry of the last pmd page.
*/
#ifdef CONFIG_X86_PAE
#define SWITCHER_PMD_INDEX (PTRS_PER_PMD - 1)
#define RESERVE_MEM 2U
#define CHECK_GPGD_MASK _PAGE_PRESENT
#else
#define RESERVE_MEM 4U
#define CHECK_GPGD_MASK _PAGE_TABLE
#endif
/*
* 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(pte_t *, switcher_pte_pages);
#define switcher_pte_page(cpu) per_cpu(switcher_pte_pages, cpu)
/*H:320
* The page table code is curly enough to need helper functions to keep it
* clear and clean. The kernel itself provides many of them; one advantage
* of insisting that the Guest and Host use the same CONFIG_PAE setting.
*
* 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 (PGD) 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 pgd_t *spgd_addr(struct lg_cpu *cpu, u32 i, unsigned long vaddr)
{
unsigned int index = pgd_index(vaddr);
#ifndef CONFIG_X86_PAE
/* We kill any Guest trying to touch the Switcher addresses. */
if (index >= SWITCHER_PGD_INDEX) {
kill_guest(cpu, "attempt to access switcher pages");
index = 0;
}
#endif
/* Return a pointer index'th pgd entry for the i'th page table. */
return &cpu->lg->pgdirs[i].pgdir[index];
}
#ifdef CONFIG_X86_PAE
/*
* This routine then takes the PGD entry given above, which contains the
* address of the PMD page. It then returns a pointer to the PMD entry for the
* given address.
*/
static pmd_t *spmd_addr(struct lg_cpu *cpu, pgd_t spgd, unsigned long vaddr)
{
unsigned int index = pmd_index(vaddr);
pmd_t *page;
/* We kill any Guest trying to touch the Switcher addresses. */
if (pgd_index(vaddr) == SWITCHER_PGD_INDEX &&
index >= SWITCHER_PMD_INDEX) {
kill_guest(cpu, "attempt to access switcher pages");
index = 0;
}
/* You should never call this if the PGD entry wasn't valid */
BUG_ON(!(pgd_flags(spgd) & _PAGE_PRESENT));
page = __va(pgd_pfn(spgd) << PAGE_SHIFT);
return &page[index];
}
#endif
/*
* This routine then takes the page directory entry returned above, which
* contains the address of the page table entry (PTE) page. It then returns a
* pointer to the PTE entry for the given address.
*/
static pte_t *spte_addr(struct lg_cpu *cpu, pgd_t spgd, unsigned long vaddr)
{
#ifdef CONFIG_X86_PAE
pmd_t *pmd = spmd_addr(cpu, spgd, vaddr);
pte_t *page = __va(pmd_pfn(*pmd) << PAGE_SHIFT);
/* You should never call this if the PMD entry wasn't valid */
BUG_ON(!(pmd_flags(*pmd) & _PAGE_PRESENT));
#else
pte_t *page = __va(pgd_pfn(spgd) << PAGE_SHIFT);
/* You should never call this if the PGD entry wasn't valid */
BUG_ON(!(pgd_flags(spgd) & _PAGE_PRESENT));
#endif
return &page[pte_index(vaddr)];
}
/*
* These functions are just like the above two, except they access the Guest
* page tables. Hence they return a Guest address.
*/
static unsigned long gpgd_addr(struct lg_cpu *cpu, unsigned long vaddr)
{
unsigned int index = vaddr >> (PGDIR_SHIFT);
return cpu->lg->pgdirs[cpu->cpu_pgd].gpgdir + index * sizeof(pgd_t);
}
#ifdef CONFIG_X86_PAE
/* Follow the PGD to the PMD. */
static unsigned long gpmd_addr(pgd_t gpgd, unsigned long vaddr)
{
unsigned long gpage = pgd_pfn(gpgd) << PAGE_SHIFT;
BUG_ON(!(pgd_flags(gpgd) & _PAGE_PRESENT));
return gpage + pmd_index(vaddr) * sizeof(pmd_t);
}
/* Follow the PMD to the PTE. */
static unsigned long gpte_addr(struct lg_cpu *cpu,
pmd_t gpmd, unsigned long vaddr)
{
unsigned long gpage = pmd_pfn(gpmd) << PAGE_SHIFT;
BUG_ON(!(pmd_flags(gpmd) & _PAGE_PRESENT));
return gpage + pte_index(vaddr) * sizeof(pte_t);
}
#else
/* Follow the PGD to the PTE (no mid-level for !PAE). */
static unsigned long gpte_addr(struct lg_cpu *cpu,
pgd_t gpgd, unsigned long vaddr)
{
unsigned long gpage = pgd_pfn(gpgd) << PAGE_SHIFT;
BUG_ON(!(pgd_flags(gpgd) & _PAGE_PRESENT));
return gpage + pte_index(vaddr) * sizeof(pte_t);
}
#endif
/*:*/
/*M:014
* get_pfn is slow: we could probably try to grab batches of pages here as
* an optimization (ie. pre-faulting).
:*/
/*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;
/* gup me one page at this address please! */
if (get_user_pages_fast(virtpfn << PAGE_SHIFT, 1, write, &page) == 1)
return page_to_pfn(page);
/* This value indicates failure. */
return -1UL;
}
/*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 pte_t gpte_to_spte(struct lg_cpu *cpu, pte_t gpte, int write)
{
unsigned long pfn, base, flags;
/*
* 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.
*/
flags = (pte_flags(gpte) & ~_PAGE_GLOBAL);
/* The Guest's pages are offset inside the Launcher. */
base = (unsigned long)cpu->lg->mem_base / PAGE_SIZE;
/*
* 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(base + pte_pfn(gpte), write);
if (pfn == -1UL) {
kill_guest(cpu, "failed to get page %lu", pte_pfn(gpte));
/*
* 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!
*/
flags = 0;
}
/* Now we assemble our shadow PTE from the page number and flags. */
return pfn_pte(pfn, __pgprot(flags));
}
/*H:460 And to complete the chain, release_pte() looks like this: */
static void release_pte(pte_t pte)
{
/*
* Remember that get_user_pages_fast() took a reference to the page, in
* get_pfn()? We have to put it back now.
*/
if (pte_flags(pte) & _PAGE_PRESENT)
put_page(pte_page(pte));
}
/*:*/
static void check_gpte(struct lg_cpu *cpu, pte_t gpte)
{
if ((pte_flags(gpte) & _PAGE_PSE) ||
pte_pfn(gpte) >= cpu->lg->pfn_limit)
kill_guest(cpu, "bad page table entry");
}
static void check_gpgd(struct lg_cpu *cpu, pgd_t gpgd)
{
if ((pgd_flags(gpgd) & ~CHECK_GPGD_MASK) ||
(pgd_pfn(gpgd) >= cpu->lg->pfn_limit))
kill_guest(cpu, "bad page directory entry");
}
#ifdef CONFIG_X86_PAE
static void check_gpmd(struct lg_cpu *cpu, pmd_t gpmd)
{
if ((pmd_flags(gpmd) & ~_PAGE_TABLE) ||
(pmd_pfn(gpmd) >= cpu->lg->pfn_limit))
kill_guest(cpu, "bad page middle directory entry");
}
#endif
/*H:330
* (i) Looking up a page table entry when the Guest 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. Otherwise, it was a real fault and we need to tell the Guest.
*/
bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
{
pgd_t gpgd;
pgd_t *spgd;
unsigned long gpte_ptr;
pte_t gpte;
pte_t *spte;
/* Mid level for PAE. */
#ifdef CONFIG_X86_PAE
pmd_t *spmd;
pmd_t gpmd;
#endif
/* First step: get the top-level Guest page table entry. */
gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t);
/* Toplevel not present? We can't map it in. */
if (!(pgd_flags(gpgd) & _PAGE_PRESENT))
return false;
/* Now look at the matching shadow entry. */
spgd = spgd_addr(cpu, cpu->cpu_pgd, vaddr);
if (!(pgd_flags(*spgd) & _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(cpu, "out of memory allocating pte page");
return false;
}
/* We check that the Guest pgd is OK. */
check_gpgd(cpu, gpgd);
/*
* And we copy the flags to the shadow PGD entry. The page
* number in the shadow PGD is the page we just allocated.
*/
set_pgd(spgd, __pgd(__pa(ptepage) | pgd_flags(gpgd)));
}
#ifdef CONFIG_X86_PAE
gpmd = lgread(cpu, gpmd_addr(gpgd, vaddr), pmd_t);
/* Middle level not present? We can't map it in. */
if (!(pmd_flags(gpmd) & _PAGE_PRESENT))
return false;
/* Now look at the matching shadow entry. */
spmd = spmd_addr(cpu, *spgd, vaddr);
if (!(pmd_flags(*spmd) & _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(cpu, "out of memory allocating pte page");
return false;
}
/* We check that the Guest pmd is OK. */
check_gpmd(cpu, gpmd);
/*
* And we copy the flags to the shadow PMD entry. The page
* number in the shadow PMD is the page we just allocated.
*/
set_pmd(spmd, __pmd(__pa(ptepage) | pmd_flags(gpmd)));
}
/*
* 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(cpu, gpmd, vaddr);
#else
/*
* 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(cpu, gpgd, vaddr);
#endif
/* Read the actual PTE value. */
gpte = lgread(cpu, gpte_ptr, pte_t);
/* If this page isn't in the Guest page tables, we can't page it in. */
if (!(pte_flags(gpte) & _PAGE_PRESENT))
return false;
/*
* Check they're not trying to write to a page the Guest wants
* read-only (bit 2 of errcode == write).
*/
if ((errcode & 2) && !(pte_flags(gpte) & _PAGE_RW))
return false;
/* User access to a kernel-only page? (bit 3 == user access) */
if ((errcode & 4) && !(pte_flags(gpte) & _PAGE_USER))
return false;
/*
* 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(cpu, gpte);
/* Add the _PAGE_ACCESSED and (for a write) _PAGE_DIRTY flag */
gpte = pte_mkyoung(gpte);
if (errcode & 2)
gpte = pte_mkdirty(gpte);
/* Get the pointer to the shadow PTE entry we're going to set. */
spte = spte_addr(cpu, *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.
*/
release_pte(*spte);
/*
* If this is a write, we insist that the Guest page is writable (the
* final arg to gpte_to_spte()).
*/
if (pte_dirty(gpte))
*spte = gpte_to_spte(cpu, 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 will come back here when a write does actually occur, so
* we can update the Guest's _PAGE_DIRTY flag.
*/
set_pte(spte, gpte_to_spte(cpu, pte_wrprotect(gpte), 0));
/*
* Finally, we write the Guest PTE entry back: we've set the
* _PAGE_ACCESSED and maybe the _PAGE_DIRTY flags.
*/
lgwrite(cpu, gpte_ptr, pte_t, gpte);
/*
* The fault is fixed, the page table is populated, the mapping
* manipulated, the result returned and the code complete. A small
* delay and a trace of alliteration are the only indications the Guest
* has that a page fault occurred at all.
*/
return true;
}
/*H:360
* (ii) Making sure the Guest stack is mapped.
*
* Remember that direct traps into the Guest need a mapped Guest kernel stack.
* pin_stack_pages() calls us here: we could simply call demand_page(), but as
* we've seen that logic is quite long, and usually the stack pages are already
* mapped, so it's overkill.
*
* This is a quick version which answers the question: is this virtual address
* mapped by the shadow page tables, and is it writable?
*/
static bool page_writable(struct lg_cpu *cpu, unsigned long vaddr)
{
pgd_t *spgd;
unsigned long flags;
#ifdef CONFIG_X86_PAE
pmd_t *spmd;
#endif
/* Look at the current top level entry: is it present? */
spgd = spgd_addr(cpu, cpu->cpu_pgd, vaddr);
if (!(pgd_flags(*spgd) & _PAGE_PRESENT))
return false;
#ifdef CONFIG_X86_PAE
spmd = spmd_addr(cpu, *spgd, vaddr);
if (!(pmd_flags(*spmd) & _PAGE_PRESENT))
return false;
#endif
/*
* Check the flags on the pte entry itself: it must be present and
* writable.
*/
flags = pte_flags(*(spte_addr(cpu, *spgd, vaddr)));
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 lg_cpu *cpu, unsigned long vaddr)
{
if (!page_writable(cpu, vaddr) && !demand_page(cpu, vaddr, 2))
kill_guest(cpu, "bad stack page %#lx", vaddr);
}
/*:*/
#ifdef CONFIG_X86_PAE
static void release_pmd(pmd_t *spmd)
{
/* If the entry's not present, there's nothing to release. */
if (pmd_flags(*spmd) & _PAGE_PRESENT) {
unsigned int i;
pte_t *ptepage = __va(pmd_pfn(*spmd) << PAGE_SHIFT);
/* For each entry in the page, we might need to release it. */
for (i = 0; i < PTRS_PER_PTE; i++)
release_pte(ptepage[i]);
/* Now we can free the page of PTEs */
free_page((long)ptepage);
/* And zero out the PMD entry so we never release it twice. */
set_pmd(spmd, __pmd(0));
}
}
static void release_pgd(pgd_t *spgd)
{
/* If the entry's not present, there's nothing to release. */
if (pgd_flags(*spgd) & _PAGE_PRESENT) {
unsigned int i;
pmd_t *pmdpage = __va(pgd_pfn(*spgd) << PAGE_SHIFT);
for (i = 0; i < PTRS_PER_PMD; i++)
release_pmd(&pmdpage[i]);
/* Now we can free the page of PMDs */
free_page((long)pmdpage);
/* And zero out the PGD entry so we never release it twice. */
set_pgd(spgd, __pgd(0));
}
}
#else /* !CONFIG_X86_PAE */
/*H:450
* If we chase down the release_pgd() code, the non-PAE version looks like
* this. The PAE version is almost identical, but instead of calling
* release_pte it calls release_pmd(), which looks much like this.
*/
static void release_pgd(pgd_t *spgd)
{
/* If the entry's not present, there's nothing to release. */
if (pgd_flags(*spgd) & _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).
*/
pte_t *ptepage = __va(pgd_pfn(*spgd) << PAGE_SHIFT);
/* For each entry in the page, we might need to release it. */
for (i = 0; i < PTRS_PER_PTE; i++)
release_pte(ptepage[i]);
/* Now we can free the page of PTEs */
free_page((long)ptepage);
/* And zero out the PGD entry so we never release it twice. */
*spgd = __pgd(0);
}
}
#endif
/*H:445
* We saw flush_user_mappings() twice: once from the flush_user_mappings()
* hypercall and once in new_pgdir() when we re-used a top-level pgdir page.
* It simply releases every PTE page from 0 up to the Guest's 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 < pgd_index(lg->kernel_address); i++)
release_pgd(lg->pgdirs[idx].pgdir + i);
}
/*H:440
* (v) Flushing (throwing away) page tables,
*
* The Guest has a hypercall to throw away the page tables: it's used when a
* large number of mappings have been changed.
*/
void guest_pagetable_flush_user(struct lg_cpu *cpu)
{
/* Drop the userspace part of the current page table. */
flush_user_mappings(cpu->lg, cpu->cpu_pgd);
}
/*:*/
/* We walk down the guest page tables to get a guest-physical address */
unsigned long guest_pa(struct lg_cpu *cpu, unsigned long vaddr)
{
pgd_t gpgd;
pte_t gpte;
#ifdef CONFIG_X86_PAE
pmd_t gpmd;
#endif
/* First step: get the top-level Guest page table entry. */
gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t);
/* Toplevel not present? We can't map it in. */
if (!(pgd_flags(gpgd) & _PAGE_PRESENT)) {
kill_guest(cpu, "Bad address %#lx", vaddr);
return -1UL;
}
#ifdef CONFIG_X86_PAE
gpmd = lgread(cpu, gpmd_addr(gpgd, vaddr), pmd_t);
if (!(pmd_flags(gpmd) & _PAGE_PRESENT))
kill_guest(cpu, "Bad address %#lx", vaddr);
gpte = lgread(cpu, gpte_addr(cpu, gpmd, vaddr), pte_t);
#else
gpte = lgread(cpu, gpte_addr(cpu, gpgd, vaddr), pte_t);
#endif
if (!(pte_flags(gpte) & _PAGE_PRESENT))
kill_guest(cpu, "Bad address %#lx", vaddr);
return pte_pfn(gpte) * PAGE_SIZE | (vaddr & ~PAGE_MASK);
}
/*
* 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].pgdir && lg->pgdirs[i].gpgdir == pgtable)
break;
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 lg_cpu *cpu,
unsigned long gpgdir,
int *blank_pgdir)
{
unsigned int next;
#ifdef CONFIG_X86_PAE
pmd_t *pmd_table;
#endif
/*
* 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(cpu->lg->pgdirs);
/* If it's never been allocated at all before, try now. */
if (!cpu->lg->pgdirs[next].pgdir) {
cpu->lg->pgdirs[next].pgdir =
(pgd_t *)get_zeroed_page(GFP_KERNEL);
/* If the allocation fails, just keep using the one we have */
if (!cpu->lg->pgdirs[next].pgdir)
next = cpu->cpu_pgd;
else {
#ifdef CONFIG_X86_PAE
/*
* In PAE mode, allocate a pmd page and populate the
* last pgd entry.
*/
pmd_table = (pmd_t *)get_zeroed_page(GFP_KERNEL);
if (!pmd_table) {
free_page((long)cpu->lg->pgdirs[next].pgdir);
set_pgd(cpu->lg->pgdirs[next].pgdir, __pgd(0));
next = cpu->cpu_pgd;
} else {
set_pgd(cpu->lg->pgdirs[next].pgdir +
SWITCHER_PGD_INDEX,
__pgd(__pa(pmd_table) | _PAGE_PRESENT));
/*
* This is a blank page, so there are no kernel
* mappings: caller must map the stack!
*/
*blank_pgdir = 1;
}
#else
*blank_pgdir = 1;
#endif
}
}
/* Record which Guest toplevel this shadows. */
cpu->lg->pgdirs[next].gpgdir = gpgdir;
/* Release all the non-kernel mappings. */
flush_user_mappings(cpu->lg, next);
return next;
}
/*H:430
* (iv) Switching page tables
*
* Now we've seen all the page table setting and manipulation, let's see
* what happens when the Guest changes page tables (ie. changes the top-level
* pgdir). This occurs on almost every context switch.
*/
void guest_new_pagetable(struct lg_cpu *cpu, unsigned long pgtable)
{
int newpgdir, repin = 0;
/* Look to see if we have this one already. */
newpgdir = find_pgdir(cpu->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(cpu->lg->pgdirs))
newpgdir = new_pgdir(cpu, pgtable, &repin);
/* Change the current pgd index to the new one. */
cpu->cpu_pgd = newpgdir;
/* If it was completely blank, we map in the Guest kernel stack */
if (repin)
pin_stack_pages(cpu);
}
/*H:470
* Finally, a routine which throws away everything: all PGD entries in all
* the shadow page tables, including the Guest's kernel mappings. 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) {
#ifdef CONFIG_X86_PAE
pgd_t *spgd;
pmd_t *pmdpage;
unsigned int k;
/* Get the last pmd page. */
spgd = lg->pgdirs[i].pgdir + SWITCHER_PGD_INDEX;
pmdpage = __va(pgd_pfn(*spgd) << PAGE_SHIFT);
/*
* And release the pmd entries of that pmd page,
* except for the switcher pmd.
*/
for (k = 0; k < SWITCHER_PMD_INDEX; k++)
release_pmd(&pmdpage[k]);
#endif
/* Every PGD entry except the Switcher at the top */
for (j = 0; j < SWITCHER_PGD_INDEX; j++)
release_pgd(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 traps the Guest in amber for a while as
* everything faults back in, but it's rare.
*/
void guest_pagetable_clear_all(struct lg_cpu *cpu)
{
release_all_pagetables(cpu->lg);
/* We need the Guest kernel stack mapped again. */
pin_stack_pages(cpu);
}
/*:*/
/*M:009
* Since we throw away all mappings when a kernel mapping changes, our
* performance sucks for guests using highmem. In fact, a guest with
* PAGE_OFFSET 0xc0000000 (the default) and more than about 700MB of RAM is
* usually slower than a Guest with less memory.
*
* This, of course, cannot be fixed. It would take some kind of... well, I
* don't know, but the term "puissant code-fu" comes to mind.
:*/
/*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 lg_cpu *cpu, int idx,
unsigned long vaddr, pte_t gpte)
{
/* Look up the matching shadow page directory entry. */
pgd_t *spgd = spgd_addr(cpu, idx, vaddr);
#ifdef CONFIG_X86_PAE
pmd_t *spmd;
#endif
/* If the top level isn't present, there's no entry to update. */
if (pgd_flags(*spgd) & _PAGE_PRESENT) {
#ifdef CONFIG_X86_PAE
spmd = spmd_addr(cpu, *spgd, vaddr);
if (pmd_flags(*spmd) & _PAGE_PRESENT) {
#endif
/* Otherwise, start by releasing the existing entry. */
pte_t *spte = spte_addr(cpu, *spgd, vaddr);
release_pte(*spte);
/*
* 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 (pte_flags(gpte) & (_PAGE_DIRTY | _PAGE_ACCESSED)) {
check_gpte(cpu, gpte);
set_pte(spte,
gpte_to_spte(cpu, gpte,
pte_flags(gpte) & _PAGE_DIRTY));
} else {
/*
* Otherwise kill it and we can demand_page()
* it in later.
*/
set_pte(spte, __pte(0));
}
#ifdef CONFIG_X86_PAE
}
#endif
}
}
/*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 keep all
* the kernel mappings. This speeds up context switch immensely.
*/
void guest_set_pte(struct lg_cpu *cpu,
unsigned long gpgdir, unsigned long vaddr, pte_t gpte)
{
/*
* Kernel mappings must be changed on all top levels. Slow, but doesn't
* happen often.
*/
if (vaddr >= cpu->lg->kernel_address) {
unsigned int i;
for (i = 0; i < ARRAY_SIZE(cpu->lg->pgdirs); i++)
if (cpu->lg->pgdirs[i].pgdir)
do_set_pte(cpu, i, vaddr, gpte);
} else {
/* Is this page table one we have a shadow for? */
int pgdir = find_pgdir(cpu->lg, gpgdir);
if (pgdir != ARRAY_SIZE(cpu->lg->pgdirs))
/* If so, do the update. */
do_set_pte(cpu, pgdir, vaddr, gpte);
}
}
/*H:400
* (iii) Setting up a page table entry when the Guest tells us one 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 update a (top-level) PGD entry:
*/
void guest_set_pgd(struct lguest *lg, unsigned long gpgdir, u32 idx)
{
int pgdir;
if (idx >= SWITCHER_PGD_INDEX)
return;
/* If they're talking about a page table we have a shadow for... */
pgdir = find_pgdir(lg, gpgdir);
if (pgdir < ARRAY_SIZE(lg->pgdirs))
/* ... throw it away. */
release_pgd(lg->pgdirs[pgdir].pgdir + idx);
}
#ifdef CONFIG_X86_PAE
/* For setting a mid-level, we just throw everything away. It's easy. */
void guest_set_pmd(struct lguest *lg, unsigned long pmdp, u32 idx)
{
guest_pagetable_clear_all(&lg->cpus[0]);
}
#endif
/*H:505
* To get through boot, we construct simple identity page mappings (which
* set virtual == physical) and linear mappings which will get the Guest far
* enough into the boot to create its own. The linear mapping means we
* simplify the Guest boot, but it makes assumptions about their PAGE_OFFSET,
* as you'll see.
*
* We lay them out of the way, just below the initrd (which is why we need to
* know its size here).
*/
static unsigned long setup_pagetables(struct lguest *lg,
unsigned long mem,
unsigned long initrd_size)
{
pgd_t __user *pgdir;
pte_t __user *linear;
unsigned long mem_base = (unsigned long)lg->mem_base;
unsigned int mapped_pages, i, linear_pages;
#ifdef CONFIG_X86_PAE
pmd_t __user *pmds;
unsigned int j;
pgd_t pgd;
pmd_t pmd;
#else
unsigned int phys_linear;
#endif
/*
* We have mapped_pages frames to map, so we need linear_pages page
* tables to map them.
*/
mapped_pages = mem / PAGE_SIZE;
linear_pages = (mapped_pages + PTRS_PER_PTE - 1) / PTRS_PER_PTE;
/* We put the toplevel page directory page at the top of memory. */
pgdir = (pgd_t *)(mem + mem_base - initrd_size - PAGE_SIZE);
/* Now we use the next linear_pages pages as pte pages */
linear = (void *)pgdir - linear_pages * PAGE_SIZE;
#ifdef CONFIG_X86_PAE
/*
* And the single mid page goes below that. We only use one, but
* that's enough to map 1G, which definitely gets us through boot.
*/
pmds = (void *)linear - PAGE_SIZE;
#endif
/*
* Linear mapping is easy: put every page's address into the
* mapping in order.
*/
for (i = 0; i < mapped_pages; i++) {
pte_t pte;
pte = pfn_pte(i, __pgprot(_PAGE_PRESENT|_PAGE_RW|_PAGE_USER));
if (copy_to_user(&linear[i], &pte, sizeof(pte)) != 0)
return -EFAULT;
}
#ifdef CONFIG_X86_PAE
/*
* Make the Guest PMD entries point to the corresponding place in the
* linear mapping (up to one page worth of PMD).
*/
for (i = j = 0; i < mapped_pages && j < PTRS_PER_PMD;
i += PTRS_PER_PTE, j++) {
pmd = pfn_pmd(((unsigned long)&linear[i] - mem_base)/PAGE_SIZE,
__pgprot(_PAGE_PRESENT | _PAGE_RW | _PAGE_USER));
if (copy_to_user(&pmds[j], &pmd, sizeof(pmd)) != 0)
return -EFAULT;
}
/* One PGD entry, pointing to that PMD page. */
pgd = __pgd(((unsigned long)pmds - mem_base) | _PAGE_PRESENT);
/* Copy it in as the first PGD entry (ie. addresses 0-1G). */
if (copy_to_user(&pgdir[0], &pgd, sizeof(pgd)) != 0)
return -EFAULT;
/*
* And the other PGD entry to make the linear mapping at PAGE_OFFSET
*/
if (copy_to_user(&pgdir[KERNEL_PGD_BOUNDARY], &pgd, sizeof(pgd)))
return -EFAULT;
#else
/*
* The top level points to the linear page table pages above.
* We setup the identity and linear mappings here.
*/
phys_linear = (unsigned long)linear - mem_base;
for (i = 0; i < mapped_pages; i += PTRS_PER_PTE) {
pgd_t pgd;
/*
* Create a PGD entry which points to the right part of the
* linear PTE pages.
*/
pgd = __pgd((phys_linear + i * sizeof(pte_t)) |
(_PAGE_PRESENT | _PAGE_RW | _PAGE_USER));
/*
* Copy it into the PGD page at 0 and PAGE_OFFSET.
*/
if (copy_to_user(&pgdir[i / PTRS_PER_PTE], &pgd, sizeof(pgd))
|| copy_to_user(&pgdir[pgd_index(PAGE_OFFSET)
+ i / PTRS_PER_PTE],
&pgd, sizeof(pgd)))
return -EFAULT;
}
#endif
/*
* We return the top level (guest-physical) address: we remember where
* this is to write it into lguest_data when the Guest initializes.
*/
return (unsigned long)pgdir - mem_base;
}
/*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)
{
u64 mem;
u32 initrd_size;
struct boot_params __user *boot = (struct boot_params *)lg->mem_base;
#ifdef CONFIG_X86_PAE
pgd_t *pgd;
pmd_t *pmd_table;
#endif
/*
* Get the Guest memory size and the ramdisk size from the boot header
* located at lg->mem_base (Guest address 0).
*/
if (copy_from_user(&mem, &boot->e820_map[0].size, sizeof(mem))
|| get_user(initrd_size, &boot->hdr.ramdisk_size))
return -EFAULT;
/*
* We start on the first shadow page table, and give it a blank PGD
* page.
*/
lg->pgdirs[0].gpgdir = setup_pagetables(lg, mem, initrd_size);
if (IS_ERR_VALUE(lg->pgdirs[0].gpgdir))
return lg->pgdirs[0].gpgdir;
lg->pgdirs[0].pgdir = (pgd_t *)get_zeroed_page(GFP_KERNEL);
if (!lg->pgdirs[0].pgdir)
return -ENOMEM;
#ifdef CONFIG_X86_PAE
/* For PAE, we also create the initial mid-level. */
pgd = lg->pgdirs[0].pgdir;
pmd_table = (pmd_t *) get_zeroed_page(GFP_KERNEL);
if (!pmd_table)
return -ENOMEM;
set_pgd(pgd + SWITCHER_PGD_INDEX,
__pgd(__pa(pmd_table) | _PAGE_PRESENT));
#endif
/* This is the current page table. */
lg->cpus[0].cpu_pgd = 0;
return 0;
}
/*H:508 When the Guest calls LHCALL_LGUEST_INIT we do more setup. */
void page_table_guest_data_init(struct lg_cpu *cpu)
{
/* We get the kernel address: above this is all kernel memory. */
if (get_user(cpu->lg->kernel_address,
&cpu->lg->lguest_data->kernel_address)
/*
* We tell the Guest that it can't use the top 2 or 4 MB
* of virtual addresses used by the Switcher.
*/
|| put_user(RESERVE_MEM * 1024 * 1024,
&cpu->lg->lguest_data->reserve_mem)
|| put_user(cpu->lg->pgdirs[0].gpgdir,
&cpu->lg->lguest_data->pgdir))
kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
/*
* In flush_user_mappings() we loop from 0 to
* "pgd_index(lg->kernel_address)". This assumes it won't hit the
* Switcher mappings, so check that now.
*/
#ifdef CONFIG_X86_PAE
if (pgd_index(cpu->lg->kernel_address) == SWITCHER_PGD_INDEX &&
pmd_index(cpu->lg->kernel_address) == SWITCHER_PMD_INDEX)
#else
if (pgd_index(cpu->lg->kernel_address) >= SWITCHER_PGD_INDEX)
#endif
kill_guest(cpu, "bad kernel address %#lx",
cpu->lg->kernel_address);
}
/* 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. */
release_all_pagetables(lg);
/* Now free the top levels: free_page() can handle 0 just fine. */
for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
free_page((long)lg->pgdirs[i].pgdir);
}
/*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 visible in 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 now we know which
* Guest is about to run on this CPU.
*/
void map_switcher_in_guest(struct lg_cpu *cpu, struct lguest_pages *pages)
{
pte_t *switcher_pte_page = __get_cpu_var(switcher_pte_pages);
pte_t regs_pte;
#ifdef CONFIG_X86_PAE
pmd_t switcher_pmd;
pmd_t *pmd_table;
switcher_pmd = pfn_pmd(__pa(switcher_pte_page) >> PAGE_SHIFT,
PAGE_KERNEL_EXEC);
/* Figure out where the pmd page is, by reading the PGD, and converting
* it to a virtual address. */
pmd_table = __va(pgd_pfn(cpu->lg->
pgdirs[cpu->cpu_pgd].pgdir[SWITCHER_PGD_INDEX])
<< PAGE_SHIFT);
/* Now write it into the shadow page table. */
set_pmd(&pmd_table[SWITCHER_PMD_INDEX], switcher_pmd);
#else
pgd_t switcher_pgd;
/*
* Make the last PGD entry for this Guest point to the Switcher's PTE
* page for this CPU (with appropriate flags).
*/
switcher_pgd = __pgd(__pa(switcher_pte_page) | __PAGE_KERNEL_EXEC);
cpu->lg->pgdirs[cpu->cpu_pgd].pgdir[SWITCHER_PGD_INDEX] = switcher_pgd;
#endif
/*
* 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_pte(__pa(cpu->regs_page) >> PAGE_SHIFT, PAGE_KERNEL);
set_pte(&switcher_pte_page[pte_index((unsigned long)pages)], regs_pte);
}
/*:*/
static void free_switcher_pte_pages(void)
{
unsigned int i;
for_each_possible_cpu(i)
free_page((long)switcher_pte_page(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;
pte_t *pte = switcher_pte_page(cpu);
/* The first entries are easy: they map the Switcher code. */
for (i = 0; i < pages; i++) {
set_pte(&pte[i], mk_pte(switcher_page[i],
__pgprot(_PAGE_PRESENT|_PAGE_ACCESSED)));
}
/* 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 */
set_pte(&pte[i], pfn_pte(page_to_pfn(switcher_page[i]),
__pgprot(_PAGE_PRESENT|_PAGE_ACCESSED|_PAGE_RW)));
/*
* The second page contains the "struct lguest_ro_state", and is
* read-only.
*/
set_pte(&pte[i+1], pfn_pte(page_to_pfn(switcher_page[i+1]),
__pgprot(_PAGE_PRESENT|_PAGE_ACCESSED)));
}
/*
* We've made it through the page table code. Perhaps our tired brains are
* still processing the details, or perhaps we're simply glad it's over.
*
* If nothing else, note that all this complexity in juggling shadow page tables
* in sync with the Guest's page tables is for one reason: for most Guests this
* page table dance determines how bad performance will be. This is why Xen
* uses exotic direct Guest pagetable manipulation, and why both Intel and AMD
* have implemented shadow page table support directly into hardware.
*
* There is just one file remaining in the Host.
*/
/*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) = (pte_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;
}
/*:*/
/* Cleaning up simply involves freeing the PTE page for each CPU. */
void free_pagetables(void)
{
free_switcher_pte_pages();
}