1197 строки
37 KiB
C
1197 строки
37 KiB
C
/*P:700
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* 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 then point the CPU to the
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* converted Guest pages when running the Guest.
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:*/
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/* Copyright (C) Rusty Russell IBM Corporation 2013.
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* GPL v2 and any later version */
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#include <linux/mm.h>
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#include <linux/gfp.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
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* 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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:*/
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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, or three-level with PAE. If
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* you're not entirely comfortable with virtual addresses, physical addresses
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* and page tables then I recommend you review arch/x86/lguest/boot.c's "Page
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* Table Handling" (with 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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/*
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* The Switcher uses the complete top PTE page. That's 1024 PTE entries (4MB)
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* or 512 PTE entries with PAE (2MB).
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*/
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#define SWITCHER_PGD_INDEX (PTRS_PER_PGD - 1)
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/*
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* For PAE we need the PMD index as well. We use the last 2MB, so we
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* will need the last pmd entry of the last pmd page.
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*/
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#ifdef CONFIG_X86_PAE
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#define CHECK_GPGD_MASK _PAGE_PRESENT
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#else
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#define CHECK_GPGD_MASK _PAGE_TABLE
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#endif
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/*H:320
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* The page table code is curly enough to need helper functions to keep it
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* clear and clean. The kernel itself provides many of them; one advantage
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* of insisting that the Guest and Host use the same CONFIG_X86_PAE setting.
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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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*/
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static pgd_t *spgd_addr(struct lg_cpu *cpu, u32 i, unsigned long vaddr)
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{
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unsigned int index = pgd_index(vaddr);
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/* Return a pointer index'th pgd entry for the i'th page table. */
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return &cpu->lg->pgdirs[i].pgdir[index];
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}
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#ifdef CONFIG_X86_PAE
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/*
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* This routine then takes the PGD entry given above, which contains the
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* address of the PMD page. It then returns a pointer to the PMD entry for the
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* given address.
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*/
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static pmd_t *spmd_addr(struct lg_cpu *cpu, pgd_t spgd, unsigned long vaddr)
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{
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unsigned int index = pmd_index(vaddr);
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pmd_t *page;
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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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page = __va(pgd_pfn(spgd) << PAGE_SHIFT);
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return &page[index];
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}
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#endif
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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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*/
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static pte_t *spte_addr(struct lg_cpu *cpu, pgd_t spgd, unsigned long vaddr)
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{
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#ifdef CONFIG_X86_PAE
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pmd_t *pmd = spmd_addr(cpu, spgd, vaddr);
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pte_t *page = __va(pmd_pfn(*pmd) << PAGE_SHIFT);
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/* You should never call this if the PMD entry wasn't valid */
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BUG_ON(!(pmd_flags(*pmd) & _PAGE_PRESENT));
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#else
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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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#endif
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return &page[pte_index(vaddr)];
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}
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/*
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* These functions are just like the above, except they access the Guest
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* page tables. Hence they return a Guest address.
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*/
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static unsigned long gpgd_addr(struct lg_cpu *cpu, unsigned long vaddr)
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{
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unsigned int index = vaddr >> (PGDIR_SHIFT);
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return cpu->lg->pgdirs[cpu->cpu_pgd].gpgdir + index * sizeof(pgd_t);
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}
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#ifdef CONFIG_X86_PAE
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/* Follow the PGD to the PMD. */
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static unsigned long gpmd_addr(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 + pmd_index(vaddr) * sizeof(pmd_t);
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}
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/* Follow the PMD to the PTE. */
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static unsigned long gpte_addr(struct lg_cpu *cpu,
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pmd_t gpmd, unsigned long vaddr)
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{
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unsigned long gpage = pmd_pfn(gpmd) << PAGE_SHIFT;
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BUG_ON(!(pmd_flags(gpmd) & _PAGE_PRESENT));
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return gpage + pte_index(vaddr) * sizeof(pte_t);
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}
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#else
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/* Follow the PGD to the PTE (no mid-level for !PAE). */
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static unsigned long gpte_addr(struct lg_cpu *cpu,
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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 + pte_index(vaddr) * sizeof(pte_t);
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}
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#endif
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/*:*/
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/*M:007
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* get_pfn is slow: we could probably try to grab batches of pages here as
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* an optimization (ie. pre-faulting).
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:*/
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/*H:350
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* 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 put that
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* back.
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*/
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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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/* gup me one page at this address please! */
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if (get_user_pages_fast(virtpfn << PAGE_SHIFT, 1, write, &page) == 1)
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return page_to_pfn(page);
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/* This value indicates failure. */
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return -1UL;
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}
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/*H:340
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* 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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*/
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static pte_t gpte_to_spte(struct lg_cpu *cpu, pte_t gpte, int write)
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{
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unsigned long pfn, base, flags;
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/*
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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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*/
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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)cpu->lg->mem_base / PAGE_SIZE;
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/*
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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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*/
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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(cpu, "failed to get page %lu", pte_pfn(gpte));
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/*
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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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*/
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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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/*
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* Remember that get_user_pages_fast() took a reference to the page, in
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* get_pfn()? We have to put it back now.
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*/
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if (pte_flags(pte) & _PAGE_PRESENT)
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put_page(pte_page(pte));
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}
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/*:*/
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static bool check_gpte(struct lg_cpu *cpu, pte_t gpte)
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{
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if ((pte_flags(gpte) & _PAGE_PSE) ||
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pte_pfn(gpte) >= cpu->lg->pfn_limit) {
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kill_guest(cpu, "bad page table entry");
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return false;
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}
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return true;
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}
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static bool check_gpgd(struct lg_cpu *cpu, pgd_t gpgd)
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{
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if ((pgd_flags(gpgd) & ~CHECK_GPGD_MASK) ||
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(pgd_pfn(gpgd) >= cpu->lg->pfn_limit)) {
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kill_guest(cpu, "bad page directory entry");
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return false;
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}
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return true;
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}
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#ifdef CONFIG_X86_PAE
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static bool check_gpmd(struct lg_cpu *cpu, pmd_t gpmd)
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{
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if ((pmd_flags(gpmd) & ~_PAGE_TABLE) ||
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(pmd_pfn(gpmd) >= cpu->lg->pfn_limit)) {
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kill_guest(cpu, "bad page middle directory entry");
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return false;
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}
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return true;
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}
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#endif
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/*H:331
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* This is the core routine to walk the shadow page tables and find the page
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* table entry for a specific address.
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*
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* If allocate is set, then we allocate any missing levels, setting the flags
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* on the new page directory and mid-level directories using the arguments
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* (which are copied from the Guest's page table entries).
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*/
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static pte_t *find_spte(struct lg_cpu *cpu, unsigned long vaddr, bool allocate,
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int pgd_flags, int pmd_flags)
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{
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pgd_t *spgd;
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/* Mid level for PAE. */
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#ifdef CONFIG_X86_PAE
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pmd_t *spmd;
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#endif
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/* Get top level entry. */
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spgd = spgd_addr(cpu, cpu->cpu_pgd, 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;
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/* If they didn't want us to allocate anything, stop. */
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if (!allocate)
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return NULL;
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ptepage = get_zeroed_page(GFP_KERNEL);
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/*
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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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*/
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if (!ptepage) {
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kill_guest(cpu, "out of memory allocating pte page");
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return NULL;
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}
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/*
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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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*/
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set_pgd(spgd, __pgd(__pa(ptepage) | pgd_flags));
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}
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/*
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* Intel's Physical Address Extension actually uses three levels of
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* page tables, so we need to look in the mid-level.
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*/
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#ifdef CONFIG_X86_PAE
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/* Now look at the mid-level shadow entry. */
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spmd = spmd_addr(cpu, *spgd, vaddr);
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if (!(pmd_flags(*spmd) & _PAGE_PRESENT)) {
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/* No shadow entry: allocate a new shadow PTE page. */
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unsigned long ptepage;
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/* If they didn't want us to allocate anything, stop. */
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if (!allocate)
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return NULL;
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ptepage = get_zeroed_page(GFP_KERNEL);
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/*
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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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*/
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if (!ptepage) {
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kill_guest(cpu, "out of memory allocating pmd page");
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return NULL;
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}
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/*
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* And we copy the flags to the shadow PMD entry. The page
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* number in the shadow PMD is the page we just allocated.
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*/
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set_pmd(spmd, __pmd(__pa(ptepage) | pmd_flags));
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}
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#endif
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/* Get the pointer to the shadow PTE entry we're going to set. */
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return spte_addr(cpu, *spgd, vaddr);
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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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*/
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bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
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{
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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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pmd_t gpmd;
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pgd_t gpgd;
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/* We never demand page the Switcher, so trying is a mistake. */
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if (vaddr >= switcher_addr)
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return false;
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/* First step: get the top-level Guest page table entry. */
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if (unlikely(cpu->linear_pages)) {
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/* Faking up a linear mapping. */
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gpgd = __pgd(CHECK_GPGD_MASK);
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} else {
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gpgd = lgread(cpu, gpgd_addr(cpu, 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 false;
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/*
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* This kills the Guest if it has weird flags or tries to
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* refer to a "physical" address outside the bounds.
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*/
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if (!check_gpgd(cpu, gpgd))
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return false;
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}
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/* This "mid-level" entry is only used for non-linear, PAE mode. */
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gpmd = __pmd(_PAGE_TABLE);
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#ifdef CONFIG_X86_PAE
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if (likely(!cpu->linear_pages)) {
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gpmd = lgread(cpu, gpmd_addr(gpgd, vaddr), pmd_t);
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/* Middle level not present? We can't map it in. */
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if (!(pmd_flags(gpmd) & _PAGE_PRESENT))
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return false;
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/*
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* This kills the Guest if it has weird flags or tries to
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* refer to a "physical" address outside the bounds.
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*/
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if (!check_gpmd(cpu, gpmd))
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return false;
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}
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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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*/
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gpte_ptr = gpte_addr(cpu, gpmd, vaddr);
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#else
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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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*/
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gpte_ptr = gpte_addr(cpu, gpgd, vaddr);
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#endif
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if (unlikely(cpu->linear_pages)) {
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/* Linear? Make up a PTE which points to same page. */
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gpte = __pte((vaddr & PAGE_MASK) | _PAGE_RW | _PAGE_PRESENT);
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} else {
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/* Read the actual PTE value. */
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gpte = lgread(cpu, gpte_ptr, pte_t);
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}
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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 false;
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/*
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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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*/
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if ((errcode & 2) && !(pte_flags(gpte) & _PAGE_RW))
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return false;
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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 false;
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/*
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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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*/
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if (!check_gpte(cpu, gpte))
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return false;
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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 = find_spte(cpu, vaddr, true, pgd_flags(gpgd), pmd_flags(gpmd));
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if (!spte)
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return false;
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/*
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* 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.
|
|
*/
|
|
if (likely(!cpu->linear_pages))
|
|
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)
|
|
{
|
|
pte_t *spte;
|
|
unsigned long flags;
|
|
|
|
/* You can't put your stack in the Switcher! */
|
|
if (vaddr >= switcher_addr)
|
|
return false;
|
|
|
|
/* If there's no shadow PTE, it's not writable. */
|
|
spte = find_spte(cpu, vaddr, false, 0, 0);
|
|
if (!spte)
|
|
return false;
|
|
|
|
/*
|
|
* Check the flags on the pte entry itself: it must be present and
|
|
* writable.
|
|
*/
|
|
flags = pte_flags(*spte);
|
|
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
|
|
|
|
/* Still not set up? Just map 1:1. */
|
|
if (unlikely(cpu->linear_pages))
|
|
return vaddr;
|
|
|
|
/* 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);
|
|
return -1UL;
|
|
}
|
|
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;
|
|
|
|
/*
|
|
* We pick one entry at random to throw out. Choosing the Least
|
|
* Recently Used might be better, but this is easy.
|
|
*/
|
|
next = prandom_u32() % 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 {
|
|
/*
|
|
* This is a blank page, so there are no kernel
|
|
* mappings: caller must map the stack!
|
|
*/
|
|
*blank_pgdir = 1;
|
|
}
|
|
}
|
|
/* Record which Guest toplevel this shadows. */
|
|
cpu->lg->pgdirs[next].gpgdir = gpgdir;
|
|
/* Release all the non-kernel mappings. */
|
|
flush_user_mappings(cpu->lg, next);
|
|
|
|
/* This hasn't run on any CPU at all. */
|
|
cpu->lg->pgdirs[next].last_host_cpu = -1;
|
|
|
|
return next;
|
|
}
|
|
|
|
/*H:501
|
|
* We do need the Switcher code mapped at all times, so we allocate that
|
|
* part of the Guest page table here. We map the Switcher code immediately,
|
|
* but defer mapping of the guest register page and IDT/LDT etc page until
|
|
* just before we run the guest in map_switcher_in_guest().
|
|
*
|
|
* We *could* do this setup in map_switcher_in_guest(), but at that point
|
|
* we've interrupts disabled, and allocating pages like that is fraught: we
|
|
* can't sleep if we need to free up some memory.
|
|
*/
|
|
static bool allocate_switcher_mapping(struct lg_cpu *cpu)
|
|
{
|
|
int i;
|
|
|
|
for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
|
|
pte_t *pte = find_spte(cpu, switcher_addr + i * PAGE_SIZE, true,
|
|
CHECK_GPGD_MASK, _PAGE_TABLE);
|
|
if (!pte)
|
|
return false;
|
|
|
|
/*
|
|
* Map the switcher page if not already there. It might
|
|
* already be there because we call allocate_switcher_mapping()
|
|
* in guest_set_pgd() just in case it did discard our Switcher
|
|
* mapping, but it probably didn't.
|
|
*/
|
|
if (i == 0 && !(pte_flags(*pte) & _PAGE_PRESENT)) {
|
|
/* Get a reference to the Switcher page. */
|
|
get_page(lg_switcher_pages[0]);
|
|
/* Create a read-only, exectuable, kernel-style PTE */
|
|
set_pte(pte,
|
|
mk_pte(lg_switcher_pages[0], PAGE_KERNEL_RX));
|
|
}
|
|
}
|
|
cpu->lg->pgdirs[cpu->cpu_pgd].switcher_mapped = true;
|
|
return true;
|
|
}
|
|
|
|
/*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)
|
|
continue;
|
|
|
|
/* Every PGD entry. */
|
|
for (j = 0; j < PTRS_PER_PGD; j++)
|
|
release_pgd(lg->pgdirs[i].pgdir + j);
|
|
lg->pgdirs[i].switcher_mapped = false;
|
|
lg->pgdirs[i].last_host_cpu = -1;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* 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);
|
|
/* And we need Switcher allocated. */
|
|
if (!allocate_switcher_mapping(cpu))
|
|
kill_guest(cpu, "Cannot populate switcher mapping");
|
|
}
|
|
|
|
/*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;
|
|
|
|
/*
|
|
* The very first time they call this, we're actually running without
|
|
* any page tables; we've been making it up. Throw them away now.
|
|
*/
|
|
if (unlikely(cpu->linear_pages)) {
|
|
release_all_pagetables(cpu->lg);
|
|
cpu->linear_pages = false;
|
|
/* Force allocation of a new pgdir. */
|
|
newpgdir = ARRAY_SIZE(cpu->lg->pgdirs);
|
|
} else {
|
|
/* 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 and
|
|
* the Switcher.
|
|
*/
|
|
if (repin)
|
|
pin_stack_pages(cpu);
|
|
|
|
if (!cpu->lg->pgdirs[cpu->cpu_pgd].switcher_mapped) {
|
|
if (!allocate_switcher_mapping(cpu))
|
|
kill_guest(cpu, "Cannot populate switcher mapping");
|
|
}
|
|
}
|
|
/*:*/
|
|
|
|
/*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 __guest_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)) {
|
|
if (!check_gpte(cpu, gpte))
|
|
return;
|
|
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)
|
|
{
|
|
/* We don't let you remap the Switcher; we need it to get back! */
|
|
if (vaddr >= switcher_addr) {
|
|
kill_guest(cpu, "attempt to set pte into Switcher pages");
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* 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)
|
|
__guest_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. */
|
|
__guest_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 > PTRS_PER_PGD) {
|
|
kill_guest(&lg->cpus[0], "Attempt to set pgd %u/%u",
|
|
idx, PTRS_PER_PGD);
|
|
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);
|
|
/* That might have been the Switcher mapping, remap it. */
|
|
if (!allocate_switcher_mapping(&lg->cpus[0])) {
|
|
kill_guest(&lg->cpus[0],
|
|
"Cannot populate switcher mapping");
|
|
}
|
|
lg->pgdirs[pgdir].last_host_cpu = -1;
|
|
}
|
|
}
|
|
|
|
#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:500
|
|
* (vii) Setting up the page tables initially.
|
|
*
|
|
* When a Guest is first created, set initialize a shadow page table which
|
|
* we will populate on future faults. The Guest doesn't have any actual
|
|
* pagetables yet, so we set linear_pages to tell demand_page() to fake it
|
|
* for the moment.
|
|
*
|
|
* We do need the Switcher to be mapped at all times, so we allocate that
|
|
* part of the Guest page table here.
|
|
*/
|
|
int init_guest_pagetable(struct lguest *lg)
|
|
{
|
|
struct lg_cpu *cpu = &lg->cpus[0];
|
|
int allocated = 0;
|
|
|
|
/* lg (and lg->cpus[]) starts zeroed: this allocates a new pgdir */
|
|
cpu->cpu_pgd = new_pgdir(cpu, 0, &allocated);
|
|
if (!allocated)
|
|
return -ENOMEM;
|
|
|
|
/* We start with a linear mapping until the initialize. */
|
|
cpu->linear_pages = true;
|
|
|
|
/* Allocate the page tables for the Switcher. */
|
|
if (!allocate_switcher_mapping(cpu)) {
|
|
release_all_pagetables(lg);
|
|
return -ENOMEM;
|
|
}
|
|
|
|
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 tell the Guest that it can't use the virtual addresses
|
|
* used by the Switcher. This trick is equivalent to 4GB -
|
|
* switcher_addr.
|
|
*/
|
|
u32 top = ~switcher_addr + 1;
|
|
|
|
/* 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 virtual
|
|
* addresses (used by the Switcher).
|
|
*/
|
|
|| put_user(top, &cpu->lg->lguest_data->reserve_mem)) {
|
|
kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* 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 (cpu->lg->kernel_address >= switcher_addr)
|
|
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:481
|
|
* This clears the Switcher mappings for cpu #i.
|
|
*/
|
|
static void remove_switcher_percpu_map(struct lg_cpu *cpu, unsigned int i)
|
|
{
|
|
unsigned long base = switcher_addr + PAGE_SIZE + i * PAGE_SIZE*2;
|
|
pte_t *pte;
|
|
|
|
/* Clear the mappings for both pages. */
|
|
pte = find_spte(cpu, base, false, 0, 0);
|
|
release_pte(*pte);
|
|
set_pte(pte, __pte(0));
|
|
|
|
pte = find_spte(cpu, base + PAGE_SIZE, false, 0, 0);
|
|
release_pte(*pte);
|
|
set_pte(pte, __pte(0));
|
|
}
|
|
|
|
/*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).
|
|
*
|
|
* The pages for the pagetables have all been allocated before: we just need
|
|
* to make sure the actual PTEs are up-to-date for the CPU we're about to run
|
|
* on.
|
|
*/
|
|
void map_switcher_in_guest(struct lg_cpu *cpu, struct lguest_pages *pages)
|
|
{
|
|
unsigned long base;
|
|
struct page *percpu_switcher_page, *regs_page;
|
|
pte_t *pte;
|
|
struct pgdir *pgdir = &cpu->lg->pgdirs[cpu->cpu_pgd];
|
|
|
|
/* Switcher page should always be mapped by now! */
|
|
BUG_ON(!pgdir->switcher_mapped);
|
|
|
|
/*
|
|
* Remember that we have two pages for each Host CPU, so we can run a
|
|
* Guest on each CPU without them interfering. We need to make sure
|
|
* those pages are mapped correctly in the Guest, but since we usually
|
|
* run on the same CPU, we cache that, and only update the mappings
|
|
* when we move.
|
|
*/
|
|
if (pgdir->last_host_cpu == raw_smp_processor_id())
|
|
return;
|
|
|
|
/* -1 means unknown so we remove everything. */
|
|
if (pgdir->last_host_cpu == -1) {
|
|
unsigned int i;
|
|
for_each_possible_cpu(i)
|
|
remove_switcher_percpu_map(cpu, i);
|
|
} else {
|
|
/* We know exactly what CPU mapping to remove. */
|
|
remove_switcher_percpu_map(cpu, pgdir->last_host_cpu);
|
|
}
|
|
|
|
/*
|
|
* 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.
|
|
*/
|
|
/* Find the shadow PTE for this regs page. */
|
|
base = switcher_addr + PAGE_SIZE
|
|
+ raw_smp_processor_id() * sizeof(struct lguest_pages);
|
|
pte = find_spte(cpu, base, false, 0, 0);
|
|
regs_page = pfn_to_page(__pa(cpu->regs_page) >> PAGE_SHIFT);
|
|
get_page(regs_page);
|
|
set_pte(pte, mk_pte(regs_page, __pgprot(__PAGE_KERNEL & ~_PAGE_GLOBAL)));
|
|
|
|
/*
|
|
* We map the second page of the struct lguest_pages read-only in
|
|
* the Guest: the IDT, GDT and other things it's not supposed to
|
|
* change.
|
|
*/
|
|
pte = find_spte(cpu, base + PAGE_SIZE, false, 0, 0);
|
|
percpu_switcher_page
|
|
= lg_switcher_pages[1 + raw_smp_processor_id()*2 + 1];
|
|
get_page(percpu_switcher_page);
|
|
set_pte(pte, mk_pte(percpu_switcher_page,
|
|
__pgprot(__PAGE_KERNEL_RO & ~_PAGE_GLOBAL)));
|
|
|
|
pgdir->last_host_cpu = raw_smp_processor_id();
|
|
}
|
|
|
|
/*H:490
|
|
* 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.
|
|
*/
|