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e1e72965ec
Went through the documentation doing typo and content fixes. This patch contains only comment and whitespace changes. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
734 lines
27 KiB
C
734 lines
27 KiB
C
/*P:700 The pagetable code, on the other hand, still shows the scars of
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* previous encounters. It's functional, and as neat as it can be in the
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* circumstances, but be wary, for these things are subtle and break easily.
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* The Guest provides a virtual to physical mapping, but we can neither trust
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* it nor use it: we verify and convert it here to point the hardware to the
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* actual Guest pages when running the Guest. :*/
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/* Copyright (C) Rusty Russell IBM Corporation 2006.
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* GPL v2 and any later version */
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#include <linux/mm.h>
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#include <linux/types.h>
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#include <linux/spinlock.h>
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#include <linux/random.h>
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#include <linux/percpu.h>
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#include <asm/tlbflush.h>
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#include <asm/uaccess.h>
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#include "lg.h"
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/*M:008 We hold reference to pages, which prevents them from being swapped.
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* It'd be nice to have a callback in the "struct mm_struct" when Linux wants
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* to swap out. If we had this, and a shrinker callback to trim PTE pages, we
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* could probably consider launching Guests as non-root. :*/
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/*H:300
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* The Page Table Code
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*
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* We use two-level page tables for the Guest. If you're not entirely
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* comfortable with virtual addresses, physical addresses and page tables then
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* I recommend you review arch/x86/lguest/boot.c's "Page Table Handling" (with
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* diagrams!).
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*
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* The Guest keeps page tables, but we maintain the actual ones here: these are
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* called "shadow" page tables. Which is a very Guest-centric name: these are
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* the real page tables the CPU uses, although we keep them up to date to
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* reflect the Guest's. (See what I mean about weird naming? Since when do
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* shadows reflect anything?)
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*
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* Anyway, this is the most complicated part of the Host code. There are seven
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* parts to this:
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* (i) Looking up a page table entry when the Guest faults,
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* (ii) Making sure the Guest stack is mapped,
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* (iii) Setting up a page table entry when the Guest tells us one has changed,
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* (iv) Switching page tables,
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* (v) Flushing (throwing away) page tables,
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* (vi) Mapping the Switcher when the Guest is about to run,
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* (vii) Setting up the page tables initially.
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:*/
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/* 1024 entries in a page table page maps 1024 pages: 4MB. The Switcher is
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* conveniently placed at the top 4MB, so it uses a separate, complete PTE
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* page. */
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#define SWITCHER_PGD_INDEX (PTRS_PER_PGD - 1)
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/* We actually need a separate PTE page for each CPU. Remember that after the
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* Switcher code itself comes two pages for each CPU, and we don't want this
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* CPU's guest to see the pages of any other CPU. */
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static DEFINE_PER_CPU(pte_t *, switcher_pte_pages);
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#define switcher_pte_page(cpu) per_cpu(switcher_pte_pages, cpu)
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/*H:320 The page table code is curly enough to need helper functions to keep it
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* clear and clean.
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*
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* There are two functions which return pointers to the shadow (aka "real")
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* page tables.
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*
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* spgd_addr() takes the virtual address and returns a pointer to the top-level
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* page directory entry (PGD) for that address. Since we keep track of several
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* page tables, the "i" argument tells us which one we're interested in (it's
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* usually the current one). */
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static pgd_t *spgd_addr(struct lguest *lg, u32 i, unsigned long vaddr)
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{
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unsigned int index = pgd_index(vaddr);
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/* We kill any Guest trying to touch the Switcher addresses. */
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if (index >= SWITCHER_PGD_INDEX) {
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kill_guest(lg, "attempt to access switcher pages");
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index = 0;
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}
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/* Return a pointer index'th pgd entry for the i'th page table. */
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return &lg->pgdirs[i].pgdir[index];
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}
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/* This routine then takes the page directory entry returned above, which
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* contains the address of the page table entry (PTE) page. It then returns a
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* pointer to the PTE entry for the given address. */
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static pte_t *spte_addr(struct lguest *lg, pgd_t spgd, unsigned long vaddr)
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{
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pte_t *page = __va(pgd_pfn(spgd) << PAGE_SHIFT);
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/* You should never call this if the PGD entry wasn't valid */
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BUG_ON(!(pgd_flags(spgd) & _PAGE_PRESENT));
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return &page[(vaddr >> PAGE_SHIFT) % PTRS_PER_PTE];
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}
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/* These two functions just like the above two, except they access the Guest
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* page tables. Hence they return a Guest address. */
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static unsigned long gpgd_addr(struct lguest *lg, unsigned long vaddr)
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{
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unsigned int index = vaddr >> (PGDIR_SHIFT);
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return lg->pgdirs[lg->pgdidx].gpgdir + index * sizeof(pgd_t);
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}
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static unsigned long gpte_addr(struct lguest *lg,
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pgd_t gpgd, unsigned long vaddr)
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{
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unsigned long gpage = pgd_pfn(gpgd) << PAGE_SHIFT;
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BUG_ON(!(pgd_flags(gpgd) & _PAGE_PRESENT));
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return gpage + ((vaddr>>PAGE_SHIFT) % PTRS_PER_PTE) * sizeof(pte_t);
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}
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/*H:350 This routine takes a page number given by the Guest and converts it to
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* an actual, physical page number. It can fail for several reasons: the
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* virtual address might not be mapped by the Launcher, the write flag is set
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* and the page is read-only, or the write flag was set and the page was
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* shared so had to be copied, but we ran out of memory.
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*
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* This holds a reference to the page, so release_pte() is careful to
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* put that back. */
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static unsigned long get_pfn(unsigned long virtpfn, int write)
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{
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struct page *page;
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/* This value indicates failure. */
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unsigned long ret = -1UL;
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/* get_user_pages() is a complex interface: it gets the "struct
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* vm_area_struct" and "struct page" assocated with a range of pages.
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* It also needs the task's mmap_sem held, and is not very quick.
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* It returns the number of pages it got. */
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down_read(¤t->mm->mmap_sem);
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if (get_user_pages(current, current->mm, virtpfn << PAGE_SHIFT,
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1, write, 1, &page, NULL) == 1)
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ret = page_to_pfn(page);
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up_read(¤t->mm->mmap_sem);
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return ret;
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}
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/*H:340 Converting a Guest page table entry to a shadow (ie. real) page table
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* entry can be a little tricky. The flags are (almost) the same, but the
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* Guest PTE contains a virtual page number: the CPU needs the real page
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* number. */
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static pte_t gpte_to_spte(struct lguest *lg, pte_t gpte, int write)
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{
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unsigned long pfn, base, flags;
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/* The Guest sets the global flag, because it thinks that it is using
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* PGE. We only told it to use PGE so it would tell us whether it was
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* flushing a kernel mapping or a userspace mapping. We don't actually
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* use the global bit, so throw it away. */
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flags = (pte_flags(gpte) & ~_PAGE_GLOBAL);
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/* The Guest's pages are offset inside the Launcher. */
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base = (unsigned long)lg->mem_base / PAGE_SIZE;
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/* We need a temporary "unsigned long" variable to hold the answer from
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* get_pfn(), because it returns 0xFFFFFFFF on failure, which wouldn't
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* fit in spte.pfn. get_pfn() finds the real physical number of the
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* page, given the virtual number. */
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pfn = get_pfn(base + pte_pfn(gpte), write);
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if (pfn == -1UL) {
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kill_guest(lg, "failed to get page %lu", pte_pfn(gpte));
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/* When we destroy the Guest, we'll go through the shadow page
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* tables and release_pte() them. Make sure we don't think
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* this one is valid! */
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flags = 0;
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}
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/* Now we assemble our shadow PTE from the page number and flags. */
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return pfn_pte(pfn, __pgprot(flags));
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}
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/*H:460 And to complete the chain, release_pte() looks like this: */
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static void release_pte(pte_t pte)
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{
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/* Remember that get_user_pages() took a reference to the page, in
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* get_pfn()? We have to put it back now. */
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if (pte_flags(pte) & _PAGE_PRESENT)
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put_page(pfn_to_page(pte_pfn(pte)));
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}
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/*:*/
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static void check_gpte(struct lguest *lg, pte_t gpte)
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{
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if ((pte_flags(gpte) & (_PAGE_PWT|_PAGE_PSE))
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|| pte_pfn(gpte) >= lg->pfn_limit)
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kill_guest(lg, "bad page table entry");
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}
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static void check_gpgd(struct lguest *lg, pgd_t gpgd)
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{
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if ((pgd_flags(gpgd) & ~_PAGE_TABLE) || pgd_pfn(gpgd) >= lg->pfn_limit)
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kill_guest(lg, "bad page directory entry");
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}
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/*H:330
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* (i) Looking up a page table entry when the Guest faults.
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*
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* We saw this call in run_guest(): when we see a page fault in the Guest, we
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* come here. That's because we only set up the shadow page tables lazily as
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* they're needed, so we get page faults all the time and quietly fix them up
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* and return to the Guest without it knowing.
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*
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* If we fixed up the fault (ie. we mapped the address), this routine returns
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* true. Otherwise, it was a real fault and we need to tell the Guest. */
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int demand_page(struct lguest *lg, unsigned long vaddr, int errcode)
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{
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pgd_t gpgd;
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pgd_t *spgd;
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unsigned long gpte_ptr;
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pte_t gpte;
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pte_t *spte;
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/* First step: get the top-level Guest page table entry. */
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gpgd = lgread(lg, gpgd_addr(lg, vaddr), pgd_t);
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/* Toplevel not present? We can't map it in. */
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if (!(pgd_flags(gpgd) & _PAGE_PRESENT))
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return 0;
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/* Now look at the matching shadow entry. */
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spgd = spgd_addr(lg, lg->pgdidx, vaddr);
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if (!(pgd_flags(*spgd) & _PAGE_PRESENT)) {
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/* No shadow entry: allocate a new shadow PTE page. */
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unsigned long ptepage = get_zeroed_page(GFP_KERNEL);
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/* This is not really the Guest's fault, but killing it is
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* simple for this corner case. */
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if (!ptepage) {
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kill_guest(lg, "out of memory allocating pte page");
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return 0;
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}
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/* We check that the Guest pgd is OK. */
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check_gpgd(lg, gpgd);
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/* And we copy the flags to the shadow PGD entry. The page
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* number in the shadow PGD is the page we just allocated. */
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*spgd = __pgd(__pa(ptepage) | pgd_flags(gpgd));
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}
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/* OK, now we look at the lower level in the Guest page table: keep its
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* address, because we might update it later. */
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gpte_ptr = gpte_addr(lg, gpgd, vaddr);
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gpte = lgread(lg, gpte_ptr, pte_t);
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/* If this page isn't in the Guest page tables, we can't page it in. */
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if (!(pte_flags(gpte) & _PAGE_PRESENT))
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return 0;
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/* Check they're not trying to write to a page the Guest wants
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* read-only (bit 2 of errcode == write). */
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if ((errcode & 2) && !(pte_flags(gpte) & _PAGE_RW))
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return 0;
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/* User access to a kernel-only page? (bit 3 == user access) */
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if ((errcode & 4) && !(pte_flags(gpte) & _PAGE_USER))
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return 0;
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/* Check that the Guest PTE flags are OK, and the page number is below
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* the pfn_limit (ie. not mapping the Launcher binary). */
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check_gpte(lg, gpte);
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/* Add the _PAGE_ACCESSED and (for a write) _PAGE_DIRTY flag */
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gpte = pte_mkyoung(gpte);
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if (errcode & 2)
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gpte = pte_mkdirty(gpte);
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/* Get the pointer to the shadow PTE entry we're going to set. */
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spte = spte_addr(lg, *spgd, vaddr);
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/* If there was a valid shadow PTE entry here before, we release it.
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* This can happen with a write to a previously read-only entry. */
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release_pte(*spte);
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/* If this is a write, we insist that the Guest page is writable (the
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* final arg to gpte_to_spte()). */
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if (pte_dirty(gpte))
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*spte = gpte_to_spte(lg, gpte, 1);
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else
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/* If this is a read, don't set the "writable" bit in the page
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* table entry, even if the Guest says it's writable. That way
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* we will come back here when a write does actually occur, so
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* we can update the Guest's _PAGE_DIRTY flag. */
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*spte = gpte_to_spte(lg, pte_wrprotect(gpte), 0);
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/* Finally, we write the Guest PTE entry back: we've set the
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* _PAGE_ACCESSED and maybe the _PAGE_DIRTY flags. */
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lgwrite(lg, gpte_ptr, pte_t, gpte);
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/* The fault is fixed, the page table is populated, the mapping
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* manipulated, the result returned and the code complete. A small
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* delay and a trace of alliteration are the only indications the Guest
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* has that a page fault occurred at all. */
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return 1;
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}
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/*H:360
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* (ii) Making sure the Guest stack is mapped.
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*
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* Remember that direct traps into the Guest need a mapped Guest kernel stack.
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* pin_stack_pages() calls us here: we could simply call demand_page(), but as
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* we've seen that logic is quite long, and usually the stack pages are already
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* mapped, so it's overkill.
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*
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* This is a quick version which answers the question: is this virtual address
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* mapped by the shadow page tables, and is it writable? */
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static int page_writable(struct lguest *lg, unsigned long vaddr)
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{
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pgd_t *spgd;
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unsigned long flags;
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/* Look at the current top level entry: is it present? */
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spgd = spgd_addr(lg, lg->pgdidx, vaddr);
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if (!(pgd_flags(*spgd) & _PAGE_PRESENT))
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return 0;
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/* Check the flags on the pte entry itself: it must be present and
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* writable. */
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flags = pte_flags(*(spte_addr(lg, *spgd, vaddr)));
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return (flags & (_PAGE_PRESENT|_PAGE_RW)) == (_PAGE_PRESENT|_PAGE_RW);
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}
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/* So, when pin_stack_pages() asks us to pin a page, we check if it's already
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* in the page tables, and if not, we call demand_page() with error code 2
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* (meaning "write"). */
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void pin_page(struct lguest *lg, unsigned long vaddr)
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{
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if (!page_writable(lg, vaddr) && !demand_page(lg, vaddr, 2))
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kill_guest(lg, "bad stack page %#lx", vaddr);
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}
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/*H:450 If we chase down the release_pgd() code, it looks like this: */
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static void release_pgd(struct lguest *lg, pgd_t *spgd)
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{
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/* If the entry's not present, there's nothing to release. */
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if (pgd_flags(*spgd) & _PAGE_PRESENT) {
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unsigned int i;
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/* Converting the pfn to find the actual PTE page is easy: turn
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* the page number into a physical address, then convert to a
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* virtual address (easy for kernel pages like this one). */
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pte_t *ptepage = __va(pgd_pfn(*spgd) << PAGE_SHIFT);
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/* For each entry in the page, we might need to release it. */
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for (i = 0; i < PTRS_PER_PTE; i++)
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release_pte(ptepage[i]);
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/* Now we can free the page of PTEs */
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free_page((long)ptepage);
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/* And zero out the PGD entry so we never release it twice. */
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*spgd = __pgd(0);
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}
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}
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/*H:445 We saw flush_user_mappings() twice: once from the flush_user_mappings()
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* hypercall and once in new_pgdir() when we re-used a top-level pgdir page.
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* It simply releases every PTE page from 0 up to the Guest's kernel address. */
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static void flush_user_mappings(struct lguest *lg, int idx)
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{
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unsigned int i;
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/* Release every pgd entry up to the kernel's address. */
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for (i = 0; i < pgd_index(lg->kernel_address); i++)
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release_pgd(lg, lg->pgdirs[idx].pgdir + i);
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}
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/*H:440 (v) Flushing (throwing away) page tables,
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*
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* The Guest has a hypercall to throw away the page tables: it's used when a
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* large number of mappings have been changed. */
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void guest_pagetable_flush_user(struct lguest *lg)
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{
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/* Drop the userspace part of the current page table. */
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flush_user_mappings(lg, lg->pgdidx);
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}
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/*:*/
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/* We walk down the guest page tables to get a guest-physical address */
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unsigned long guest_pa(struct lguest *lg, unsigned long vaddr)
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{
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pgd_t gpgd;
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pte_t gpte;
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/* First step: get the top-level Guest page table entry. */
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gpgd = lgread(lg, gpgd_addr(lg, vaddr), pgd_t);
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/* Toplevel not present? We can't map it in. */
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if (!(pgd_flags(gpgd) & _PAGE_PRESENT))
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kill_guest(lg, "Bad address %#lx", vaddr);
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gpte = lgread(lg, gpte_addr(lg, gpgd, vaddr), pte_t);
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if (!(pte_flags(gpte) & _PAGE_PRESENT))
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kill_guest(lg, "Bad address %#lx", vaddr);
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return pte_pfn(gpte) * PAGE_SIZE | (vaddr & ~PAGE_MASK);
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}
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/* We keep several page tables. This is a simple routine to find the page
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* table (if any) corresponding to this top-level address the Guest has given
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* us. */
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static unsigned int find_pgdir(struct lguest *lg, unsigned long pgtable)
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{
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unsigned int i;
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for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
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if (lg->pgdirs[i].gpgdir == pgtable)
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break;
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return i;
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}
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/*H:435 And this is us, creating the new page directory. If we really do
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* allocate a new one (and so the kernel parts are not there), we set
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* blank_pgdir. */
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static unsigned int new_pgdir(struct lguest *lg,
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unsigned long gpgdir,
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int *blank_pgdir)
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{
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unsigned int next;
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/* We pick one entry at random to throw out. Choosing the Least
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* Recently Used might be better, but this is easy. */
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next = random32() % ARRAY_SIZE(lg->pgdirs);
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/* If it's never been allocated at all before, try now. */
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if (!lg->pgdirs[next].pgdir) {
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lg->pgdirs[next].pgdir = (pgd_t *)get_zeroed_page(GFP_KERNEL);
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/* If the allocation fails, just keep using the one we have */
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if (!lg->pgdirs[next].pgdir)
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next = lg->pgdidx;
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else
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/* This is a blank page, so there are no kernel
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* mappings: caller must map the stack! */
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*blank_pgdir = 1;
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}
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/* Record which Guest toplevel this shadows. */
|
|
lg->pgdirs[next].gpgdir = gpgdir;
|
|
/* Release all the non-kernel mappings. */
|
|
flush_user_mappings(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
|
|
* 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 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)
|
|
pin_stack_pages(lg);
|
|
}
|
|
|
|
/*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)
|
|
/* 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 traps the Guest in amber for a while as
|
|
* everything faults back in, but it's rare. */
|
|
void guest_pagetable_clear_all(struct lguest *lg)
|
|
{
|
|
release_all_pagetables(lg);
|
|
/* We need the Guest kernel stack mapped again. */
|
|
pin_stack_pages(lg);
|
|
}
|
|
/*:*/
|
|
/*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 lguest *lg, int idx,
|
|
unsigned long vaddr, pte_t gpte)
|
|
{
|
|
/* Look up the matching shadow page directory entry. */
|
|
pgd_t *spgd = spgd_addr(lg, idx, vaddr);
|
|
|
|
/* If the top level isn't present, there's no entry to update. */
|
|
if (pgd_flags(*spgd) & _PAGE_PRESENT) {
|
|
/* Otherwise, we start by releasing the existing entry. */
|
|
pte_t *spte = spte_addr(lg, *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(lg, gpte);
|
|
*spte = gpte_to_spte(lg, gpte,
|
|
pte_flags(gpte) & _PAGE_DIRTY);
|
|
} else
|
|
/* Otherwise kill it and we can demand_page() it in
|
|
* later. */
|
|
*spte = __pte(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 gpgdir, unsigned long vaddr, pte_t gpte)
|
|
{
|
|
/* Kernel mappings must be changed on all top levels. Slow, but
|
|
* doesn't happen often. */
|
|
if (vaddr >= lg->kernel_address) {
|
|
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, gpgdir);
|
|
if (pgdir != ARRAY_SIZE(lg->pgdirs))
|
|
/* If so, do the update. */
|
|
do_set_pte(lg, 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 to update a (top-level) PGD entry:
|
|
*/
|
|
void guest_set_pmd(struct lguest *lg, unsigned long gpgdir, u32 idx)
|
|
{
|
|
int pgdir;
|
|
|
|
/* The kernel seems to try to initialize this early on: we ignore its
|
|
* attempts to map over the Switcher. */
|
|
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, 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)
|
|
{
|
|
/* We start on the first shadow page table, and give it a blank PGD
|
|
* page. */
|
|
lg->pgdidx = 0;
|
|
lg->pgdirs[lg->pgdidx].gpgdir = pgtable;
|
|
lg->pgdirs[lg->pgdidx].pgdir = (pgd_t*)get_zeroed_page(GFP_KERNEL);
|
|
if (!lg->pgdirs[lg->pgdidx].pgdir)
|
|
return -ENOMEM;
|
|
return 0;
|
|
}
|
|
|
|
/* When the Guest calls LHCALL_LGUEST_INIT we do more setup. */
|
|
void page_table_guest_data_init(struct lguest *lg)
|
|
{
|
|
/* We get the kernel address: above this is all kernel memory. */
|
|
if (get_user(lg->kernel_address, &lg->lguest_data->kernel_address)
|
|
/* We tell the Guest that it can't use the top 4MB of virtual
|
|
* addresses used by the Switcher. */
|
|
|| put_user(4U*1024*1024, &lg->lguest_data->reserve_mem)
|
|
|| put_user(lg->pgdirs[lg->pgdidx].gpgdir,&lg->lguest_data->pgdir))
|
|
kill_guest(lg, "bad guest page %p", 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. */
|
|
if (pgd_index(lg->kernel_address) >= SWITCHER_PGD_INDEX)
|
|
kill_guest(lg, "bad kernel address %#lx", 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 lguest *lg, struct lguest_pages *pages)
|
|
{
|
|
pte_t *switcher_pte_page = __get_cpu_var(switcher_pte_pages);
|
|
pgd_t switcher_pgd;
|
|
pte_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 = __pgd(__pa(switcher_pte_page) | _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_pte (__pa(lg->regs_page) >> PAGE_SHIFT, __pgprot(_PAGE_KERNEL));
|
|
switcher_pte_page[(unsigned long)pages/PAGE_SIZE%PTRS_PER_PTE] = 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++) {
|
|
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 */
|
|
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. */
|
|
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();
|
|
}
|