/* * linux/mm/fremap.c * * Explicit pagetable population and nonlinear (random) mappings support. * * started by Ingo Molnar, Copyright (C) 2002, 2003 */ #include <linux/backing-dev.h> #include <linux/mm.h> #include <linux/swap.h> #include <linux/file.h> #include <linux/mman.h> #include <linux/pagemap.h> #include <linux/swapops.h> #include <linux/rmap.h> #include <linux/module.h> #include <linux/syscalls.h> #include <asm/mmu_context.h> #include <asm/cacheflush.h> #include <asm/tlbflush.h> static void zap_pte(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long addr, pte_t *ptep) { pte_t pte = *ptep; if (pte_present(pte)) { struct page *page; flush_cache_page(vma, addr, pte_pfn(pte)); pte = ptep_clear_flush(vma, addr, ptep); page = vm_normal_page(vma, addr, pte); if (page) { if (pte_dirty(pte)) set_page_dirty(page); page_remove_rmap(page, vma); page_cache_release(page); update_hiwater_rss(mm); dec_mm_counter(mm, file_rss); } } else { if (!pte_file(pte)) free_swap_and_cache(pte_to_swp_entry(pte)); pte_clear_not_present_full(mm, addr, ptep, 0); } } /* * Install a file pte to a given virtual memory address, release any * previously existing mapping. */ static int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long addr, unsigned long pgoff, pgprot_t prot) { int err = -ENOMEM; pte_t *pte; spinlock_t *ptl; pte = get_locked_pte(mm, addr, &ptl); if (!pte) goto out; if (!pte_none(*pte)) zap_pte(mm, vma, addr, pte); set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff)); /* * We don't need to run update_mmu_cache() here because the "file pte" * being installed by install_file_pte() is not a real pte - it's a * non-present entry (like a swap entry), noting what file offset should * be mapped there when there's a fault (in a non-linear vma where * that's not obvious). */ pte_unmap_unlock(pte, ptl); err = 0; out: return err; } static int populate_range(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long addr, unsigned long size, pgoff_t pgoff) { int err; do { err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot); if (err) return err; size -= PAGE_SIZE; addr += PAGE_SIZE; pgoff++; } while (size); return 0; } /** * sys_remap_file_pages - remap arbitrary pages of an existing VM_SHARED vma * @start: start of the remapped virtual memory range * @size: size of the remapped virtual memory range * @prot: new protection bits of the range (see NOTE) * @pgoff: to-be-mapped page of the backing store file * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO. * * sys_remap_file_pages remaps arbitrary pages of an existing VM_SHARED vma * (shared backing store file). * * This syscall works purely via pagetables, so it's the most efficient * way to map the same (large) file into a given virtual window. Unlike * mmap()/mremap() it does not create any new vmas. The new mappings are * also safe across swapout. * * NOTE: the 'prot' parameter right now is ignored (but must be zero), * and the vma's default protection is used. Arbitrary protections * might be implemented in the future. */ asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size, unsigned long prot, unsigned long pgoff, unsigned long flags) { struct mm_struct *mm = current->mm; struct address_space *mapping; unsigned long end = start + size; struct vm_area_struct *vma; int err = -EINVAL; int has_write_lock = 0; if (prot) return err; /* * Sanitize the syscall parameters: */ start = start & PAGE_MASK; size = size & PAGE_MASK; /* Does the address range wrap, or is the span zero-sized? */ if (start + size <= start) return err; /* Can we represent this offset inside this architecture's pte's? */ #if PTE_FILE_MAX_BITS < BITS_PER_LONG if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS)) return err; #endif /* We need down_write() to change vma->vm_flags. */ down_read(&mm->mmap_sem); retry: vma = find_vma(mm, start); /* * Make sure the vma is shared, that it supports prefaulting, * and that the remapped range is valid and fully within * the single existing vma. vm_private_data is used as a * swapout cursor in a VM_NONLINEAR vma. */ if (!vma || !(vma->vm_flags & VM_SHARED)) goto out; if (vma->vm_private_data && !(vma->vm_flags & VM_NONLINEAR)) goto out; if (!(vma->vm_flags & VM_CAN_NONLINEAR)) goto out; if (end <= start || start < vma->vm_start || end > vma->vm_end) goto out; /* Must set VM_NONLINEAR before any pages are populated. */ if (!(vma->vm_flags & VM_NONLINEAR)) { /* Don't need a nonlinear mapping, exit success */ if (pgoff == linear_page_index(vma, start)) { err = 0; goto out; } if (!has_write_lock) { up_read(&mm->mmap_sem); down_write(&mm->mmap_sem); has_write_lock = 1; goto retry; } mapping = vma->vm_file->f_mapping; /* * page_mkclean doesn't work on nonlinear vmas, so if * dirty pages need to be accounted, emulate with linear * vmas. */ if (mapping_cap_account_dirty(mapping)) { unsigned long addr; struct file *file = vma->vm_file; flags &= MAP_NONBLOCK; get_file(file); addr = mmap_region(file, start, size, flags, vma->vm_flags, pgoff, 1); fput(file); if (IS_ERR_VALUE(addr)) { err = addr; } else { BUG_ON(addr != start); err = 0; } goto out; } spin_lock(&mapping->i_mmap_lock); flush_dcache_mmap_lock(mapping); vma->vm_flags |= VM_NONLINEAR; vma_prio_tree_remove(vma, &mapping->i_mmap); vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear); flush_dcache_mmap_unlock(mapping); spin_unlock(&mapping->i_mmap_lock); } err = populate_range(mm, vma, start, size, pgoff); if (!err && !(flags & MAP_NONBLOCK)) { if (unlikely(has_write_lock)) { downgrade_write(&mm->mmap_sem); has_write_lock = 0; } make_pages_present(start, start+size); } /* * We can't clear VM_NONLINEAR because we'd have to do * it after ->populate completes, and that would prevent * downgrading the lock. (Locks can't be upgraded). */ out: if (likely(!has_write_lock)) up_read(&mm->mmap_sem); else up_write(&mm->mmap_sem); return err; }