fremap.c revision d0217ac04ca6591841e5665f518e38064f4e65bd
1/* 2 * linux/mm/fremap.c 3 * 4 * Explicit pagetable population and nonlinear (random) mappings support. 5 * 6 * started by Ingo Molnar, Copyright (C) 2002, 2003 7 */ 8 9#include <linux/mm.h> 10#include <linux/swap.h> 11#include <linux/file.h> 12#include <linux/mman.h> 13#include <linux/pagemap.h> 14#include <linux/swapops.h> 15#include <linux/rmap.h> 16#include <linux/module.h> 17#include <linux/syscalls.h> 18 19#include <asm/mmu_context.h> 20#include <asm/cacheflush.h> 21#include <asm/tlbflush.h> 22 23static void zap_pte(struct mm_struct *mm, struct vm_area_struct *vma, 24 unsigned long addr, pte_t *ptep) 25{ 26 pte_t pte = *ptep; 27 28 if (pte_present(pte)) { 29 struct page *page; 30 31 flush_cache_page(vma, addr, pte_pfn(pte)); 32 pte = ptep_clear_flush(vma, addr, ptep); 33 page = vm_normal_page(vma, addr, pte); 34 if (page) { 35 if (pte_dirty(pte)) 36 set_page_dirty(page); 37 page_remove_rmap(page, vma); 38 page_cache_release(page); 39 update_hiwater_rss(mm); 40 dec_mm_counter(mm, file_rss); 41 } 42 } else { 43 if (!pte_file(pte)) 44 free_swap_and_cache(pte_to_swp_entry(pte)); 45 pte_clear_not_present_full(mm, addr, ptep, 0); 46 } 47} 48 49/* 50 * Install a file pte to a given virtual memory address, release any 51 * previously existing mapping. 52 */ 53static int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma, 54 unsigned long addr, unsigned long pgoff, pgprot_t prot) 55{ 56 int err = -ENOMEM; 57 pte_t *pte; 58 spinlock_t *ptl; 59 60 pte = get_locked_pte(mm, addr, &ptl); 61 if (!pte) 62 goto out; 63 64 if (!pte_none(*pte)) 65 zap_pte(mm, vma, addr, pte); 66 67 set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff)); 68 /* 69 * We don't need to run update_mmu_cache() here because the "file pte" 70 * being installed by install_file_pte() is not a real pte - it's a 71 * non-present entry (like a swap entry), noting what file offset should 72 * be mapped there when there's a fault (in a non-linear vma where 73 * that's not obvious). 74 */ 75 pte_unmap_unlock(pte, ptl); 76 err = 0; 77out: 78 return err; 79} 80 81static int populate_range(struct mm_struct *mm, struct vm_area_struct *vma, 82 unsigned long addr, unsigned long size, pgoff_t pgoff) 83{ 84 int err; 85 86 do { 87 err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot); 88 if (err) 89 return err; 90 91 size -= PAGE_SIZE; 92 addr += PAGE_SIZE; 93 pgoff++; 94 } while (size); 95 96 return 0; 97 98} 99 100/*** 101 * sys_remap_file_pages - remap arbitrary pages of a shared backing store 102 * file within an existing vma. 103 * @start: start of the remapped virtual memory range 104 * @size: size of the remapped virtual memory range 105 * @prot: new protection bits of the range 106 * @pgoff: to be mapped page of the backing store file 107 * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO. 108 * 109 * this syscall works purely via pagetables, so it's the most efficient 110 * way to map the same (large) file into a given virtual window. Unlike 111 * mmap()/mremap() it does not create any new vmas. The new mappings are 112 * also safe across swapout. 113 * 114 * NOTE: the 'prot' parameter right now is ignored, and the vma's default 115 * protection is used. Arbitrary protections might be implemented in the 116 * future. 117 */ 118asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size, 119 unsigned long __prot, unsigned long pgoff, unsigned long flags) 120{ 121 struct mm_struct *mm = current->mm; 122 struct address_space *mapping; 123 unsigned long end = start + size; 124 struct vm_area_struct *vma; 125 int err = -EINVAL; 126 int has_write_lock = 0; 127 128 if (__prot) 129 return err; 130 /* 131 * Sanitize the syscall parameters: 132 */ 133 start = start & PAGE_MASK; 134 size = size & PAGE_MASK; 135 136 /* Does the address range wrap, or is the span zero-sized? */ 137 if (start + size <= start) 138 return err; 139 140 /* Can we represent this offset inside this architecture's pte's? */ 141#if PTE_FILE_MAX_BITS < BITS_PER_LONG 142 if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS)) 143 return err; 144#endif 145 146 /* We need down_write() to change vma->vm_flags. */ 147 down_read(&mm->mmap_sem); 148 retry: 149 vma = find_vma(mm, start); 150 151 /* 152 * Make sure the vma is shared, that it supports prefaulting, 153 * and that the remapped range is valid and fully within 154 * the single existing vma. vm_private_data is used as a 155 * swapout cursor in a VM_NONLINEAR vma. 156 */ 157 if (!vma || !(vma->vm_flags & VM_SHARED)) 158 goto out; 159 160 if (vma->vm_private_data && !(vma->vm_flags & VM_NONLINEAR)) 161 goto out; 162 163 if (!vma->vm_flags & VM_CAN_NONLINEAR) 164 goto out; 165 166 if (end <= start || start < vma->vm_start || end > vma->vm_end) 167 goto out; 168 169 /* Must set VM_NONLINEAR before any pages are populated. */ 170 if (!(vma->vm_flags & VM_NONLINEAR)) { 171 /* Don't need a nonlinear mapping, exit success */ 172 if (pgoff == linear_page_index(vma, start)) { 173 err = 0; 174 goto out; 175 } 176 177 if (!has_write_lock) { 178 up_read(&mm->mmap_sem); 179 down_write(&mm->mmap_sem); 180 has_write_lock = 1; 181 goto retry; 182 } 183 mapping = vma->vm_file->f_mapping; 184 spin_lock(&mapping->i_mmap_lock); 185 flush_dcache_mmap_lock(mapping); 186 vma->vm_flags |= VM_NONLINEAR; 187 vma_prio_tree_remove(vma, &mapping->i_mmap); 188 vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear); 189 flush_dcache_mmap_unlock(mapping); 190 spin_unlock(&mapping->i_mmap_lock); 191 } 192 193 err = populate_range(mm, vma, start, size, pgoff); 194 if (!err && !(flags & MAP_NONBLOCK)) { 195 if (unlikely(has_write_lock)) { 196 downgrade_write(&mm->mmap_sem); 197 has_write_lock = 0; 198 } 199 make_pages_present(start, start+size); 200 } 201 202 /* 203 * We can't clear VM_NONLINEAR because we'd have to do 204 * it after ->populate completes, and that would prevent 205 * downgrading the lock. (Locks can't be upgraded). 206 */ 207 208out: 209 if (likely(!has_write_lock)) 210 up_read(&mm->mmap_sem); 211 else 212 up_write(&mm->mmap_sem); 213 214 return err; 215} 216 217