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![Michel Lespinasse](/assets/img/avatar_default.png)
This reverts commit 1869305009
("mm: introduce VM_POPULATE flag to
better deal with racy userspace programs").
VM_POPULATE only has any effect when userspace plays racy games with
vmas by trying to unmap and remap memory regions that mmap or mlock are
operating on.
Also, the only effect of VM_POPULATE when userspace plays such games is
that it avoids populating new memory regions that get remapped into the
address range that was being operated on by the original mmap or mlock
calls.
Let's remove VM_POPULATE as there isn't any strong argument to mandate a
new vm_flag.
Signed-off-by: Michel Lespinasse <walken@google.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
259 lines
6.6 KiB
C
259 lines
6.6 KiB
C
/*
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* linux/mm/fremap.c
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*
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* Explicit pagetable population and nonlinear (random) mappings support.
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*
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* started by Ingo Molnar, Copyright (C) 2002, 2003
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*/
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#include <linux/export.h>
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#include <linux/backing-dev.h>
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#include <linux/mm.h>
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#include <linux/swap.h>
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#include <linux/file.h>
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#include <linux/mman.h>
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#include <linux/pagemap.h>
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#include <linux/swapops.h>
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#include <linux/rmap.h>
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#include <linux/syscalls.h>
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#include <linux/mmu_notifier.h>
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#include <asm/mmu_context.h>
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#include <asm/cacheflush.h>
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#include <asm/tlbflush.h>
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#include "internal.h"
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static void zap_pte(struct mm_struct *mm, struct vm_area_struct *vma,
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unsigned long addr, pte_t *ptep)
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{
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pte_t pte = *ptep;
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if (pte_present(pte)) {
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struct page *page;
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flush_cache_page(vma, addr, pte_pfn(pte));
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pte = ptep_clear_flush(vma, addr, ptep);
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page = vm_normal_page(vma, addr, pte);
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if (page) {
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if (pte_dirty(pte))
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set_page_dirty(page);
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page_remove_rmap(page);
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page_cache_release(page);
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update_hiwater_rss(mm);
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dec_mm_counter(mm, MM_FILEPAGES);
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}
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} else {
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if (!pte_file(pte))
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free_swap_and_cache(pte_to_swp_entry(pte));
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pte_clear_not_present_full(mm, addr, ptep, 0);
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}
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}
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/*
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* Install a file pte to a given virtual memory address, release any
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* previously existing mapping.
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*/
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static int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
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unsigned long addr, unsigned long pgoff, pgprot_t prot)
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{
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int err = -ENOMEM;
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pte_t *pte;
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spinlock_t *ptl;
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pte = get_locked_pte(mm, addr, &ptl);
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if (!pte)
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goto out;
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if (!pte_none(*pte))
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zap_pte(mm, vma, addr, pte);
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set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));
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/*
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* We don't need to run update_mmu_cache() here because the "file pte"
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* being installed by install_file_pte() is not a real pte - it's a
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* non-present entry (like a swap entry), noting what file offset should
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* be mapped there when there's a fault (in a non-linear vma where
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* that's not obvious).
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*/
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pte_unmap_unlock(pte, ptl);
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err = 0;
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out:
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return err;
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}
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int generic_file_remap_pages(struct vm_area_struct *vma, unsigned long addr,
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unsigned long size, pgoff_t pgoff)
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{
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struct mm_struct *mm = vma->vm_mm;
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int err;
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do {
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err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot);
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if (err)
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return err;
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size -= PAGE_SIZE;
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addr += PAGE_SIZE;
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pgoff++;
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} while (size);
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return 0;
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}
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EXPORT_SYMBOL(generic_file_remap_pages);
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/**
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* sys_remap_file_pages - remap arbitrary pages of an existing VM_SHARED vma
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* @start: start of the remapped virtual memory range
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* @size: size of the remapped virtual memory range
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* @prot: new protection bits of the range (see NOTE)
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* @pgoff: to-be-mapped page of the backing store file
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* @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
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*
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* sys_remap_file_pages remaps arbitrary pages of an existing VM_SHARED vma
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* (shared backing store file).
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*
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* This syscall works purely via pagetables, so it's the most efficient
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* way to map the same (large) file into a given virtual window. Unlike
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* mmap()/mremap() it does not create any new vmas. The new mappings are
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* also safe across swapout.
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*
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* NOTE: the @prot parameter right now is ignored (but must be zero),
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* and the vma's default protection is used. Arbitrary protections
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* might be implemented in the future.
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*/
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SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
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unsigned long, prot, unsigned long, pgoff, unsigned long, flags)
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{
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struct mm_struct *mm = current->mm;
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struct address_space *mapping;
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struct vm_area_struct *vma;
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int err = -EINVAL;
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int has_write_lock = 0;
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vm_flags_t vm_flags = 0;
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if (prot)
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return err;
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/*
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* Sanitize the syscall parameters:
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*/
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start = start & PAGE_MASK;
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size = size & PAGE_MASK;
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/* Does the address range wrap, or is the span zero-sized? */
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if (start + size <= start)
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return err;
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/* Does pgoff wrap? */
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if (pgoff + (size >> PAGE_SHIFT) < pgoff)
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return err;
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/* Can we represent this offset inside this architecture's pte's? */
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#if PTE_FILE_MAX_BITS < BITS_PER_LONG
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if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
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return err;
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#endif
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/* We need down_write() to change vma->vm_flags. */
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down_read(&mm->mmap_sem);
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retry:
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vma = find_vma(mm, start);
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/*
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* Make sure the vma is shared, that it supports prefaulting,
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* and that the remapped range is valid and fully within
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* the single existing vma.
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*/
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if (!vma || !(vma->vm_flags & VM_SHARED))
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goto out;
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if (!vma->vm_ops || !vma->vm_ops->remap_pages)
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goto out;
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if (start < vma->vm_start || start + size > vma->vm_end)
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goto out;
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/* Must set VM_NONLINEAR before any pages are populated. */
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if (!(vma->vm_flags & VM_NONLINEAR)) {
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/*
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* vm_private_data is used as a swapout cursor
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* in a VM_NONLINEAR vma.
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*/
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if (vma->vm_private_data)
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goto out;
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/* Don't need a nonlinear mapping, exit success */
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if (pgoff == linear_page_index(vma, start)) {
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err = 0;
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goto out;
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}
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if (!has_write_lock) {
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get_write_lock:
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up_read(&mm->mmap_sem);
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down_write(&mm->mmap_sem);
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has_write_lock = 1;
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goto retry;
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}
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mapping = vma->vm_file->f_mapping;
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/*
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* page_mkclean doesn't work on nonlinear vmas, so if
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* dirty pages need to be accounted, emulate with linear
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* vmas.
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*/
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if (mapping_cap_account_dirty(mapping)) {
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unsigned long addr;
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struct file *file = get_file(vma->vm_file);
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addr = mmap_region(file, start, size,
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vma->vm_flags, pgoff);
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fput(file);
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if (IS_ERR_VALUE(addr)) {
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err = addr;
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} else {
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BUG_ON(addr != start);
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err = 0;
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}
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goto out;
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}
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mutex_lock(&mapping->i_mmap_mutex);
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flush_dcache_mmap_lock(mapping);
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vma->vm_flags |= VM_NONLINEAR;
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vma_interval_tree_remove(vma, &mapping->i_mmap);
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vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
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flush_dcache_mmap_unlock(mapping);
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mutex_unlock(&mapping->i_mmap_mutex);
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}
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if (vma->vm_flags & VM_LOCKED) {
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/*
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* drop PG_Mlocked flag for over-mapped range
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*/
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if (!has_write_lock)
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goto get_write_lock;
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vm_flags = vma->vm_flags;
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munlock_vma_pages_range(vma, start, start + size);
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vma->vm_flags = vm_flags;
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}
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mmu_notifier_invalidate_range_start(mm, start, start + size);
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err = vma->vm_ops->remap_pages(vma, start, size, pgoff);
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mmu_notifier_invalidate_range_end(mm, start, start + size);
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/*
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* We can't clear VM_NONLINEAR because we'd have to do
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* it after ->populate completes, and that would prevent
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* downgrading the lock. (Locks can't be upgraded).
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*/
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out:
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if (vma)
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vm_flags = vma->vm_flags;
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if (likely(!has_write_lock))
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up_read(&mm->mmap_sem);
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else
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up_write(&mm->mmap_sem);
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if (!err && ((vm_flags & VM_LOCKED) || !(flags & MAP_NONBLOCK)))
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mm_populate(start, size);
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return err;
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}
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