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![Michael S. Tsirkin](/assets/img/avatar_default.png)
Currently, copy-on-write may change the physical address of a page even if the user requested that the page is pinned in memory (either by mlock or by get_user_pages). This happens if the process forks meanwhile, and the parent writes to that page. As a result, the page is orphaned: in case of get_user_pages, the application will never see any data hardware DMA's into this page after the COW. In case of mlock'd memory, the parent is not getting the realtime/security benefits of mlock. In particular, this affects the Infiniband modules which do DMA from and into user pages all the time. This patch adds madvise options to control whether memory range is inherited across fork. Useful e.g. for when hardware is doing DMA from/into these pages. Could also be useful to an application wanting to speed up its forks by cutting large areas out of consideration. Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il> Acked-by: Hugh Dickins <hugh@veritas.com> Cc: Michael Kerrisk <mtk-manpages@gmx.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
322 lines
8.5 KiB
C
322 lines
8.5 KiB
C
/*
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* linux/mm/madvise.c
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*
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* Copyright (C) 1999 Linus Torvalds
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* Copyright (C) 2002 Christoph Hellwig
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*/
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#include <linux/mman.h>
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#include <linux/pagemap.h>
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#include <linux/syscalls.h>
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#include <linux/mempolicy.h>
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#include <linux/hugetlb.h>
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/*
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* We can potentially split a vm area into separate
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* areas, each area with its own behavior.
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*/
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static long madvise_behavior(struct vm_area_struct * vma,
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struct vm_area_struct **prev,
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unsigned long start, unsigned long end, int behavior)
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{
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struct mm_struct * mm = vma->vm_mm;
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int error = 0;
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pgoff_t pgoff;
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int new_flags = vma->vm_flags;
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switch (behavior) {
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case MADV_NORMAL:
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new_flags = new_flags & ~VM_RAND_READ & ~VM_SEQ_READ;
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break;
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case MADV_SEQUENTIAL:
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new_flags = (new_flags & ~VM_RAND_READ) | VM_SEQ_READ;
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break;
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case MADV_RANDOM:
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new_flags = (new_flags & ~VM_SEQ_READ) | VM_RAND_READ;
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break;
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case MADV_DONTFORK:
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new_flags |= VM_DONTCOPY;
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break;
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case MADV_DOFORK:
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new_flags &= ~VM_DONTCOPY;
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break;
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}
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if (new_flags == vma->vm_flags) {
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*prev = vma;
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goto out;
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}
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pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
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*prev = vma_merge(mm, *prev, start, end, new_flags, vma->anon_vma,
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vma->vm_file, pgoff, vma_policy(vma));
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if (*prev) {
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vma = *prev;
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goto success;
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}
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*prev = vma;
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if (start != vma->vm_start) {
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error = split_vma(mm, vma, start, 1);
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if (error)
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goto out;
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}
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if (end != vma->vm_end) {
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error = split_vma(mm, vma, end, 0);
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if (error)
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goto out;
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}
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success:
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/*
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* vm_flags is protected by the mmap_sem held in write mode.
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*/
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vma->vm_flags = new_flags;
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out:
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if (error == -ENOMEM)
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error = -EAGAIN;
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return error;
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}
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/*
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* Schedule all required I/O operations. Do not wait for completion.
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*/
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static long madvise_willneed(struct vm_area_struct * vma,
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struct vm_area_struct ** prev,
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unsigned long start, unsigned long end)
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{
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struct file *file = vma->vm_file;
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if (!file)
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return -EBADF;
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if (file->f_mapping->a_ops->get_xip_page) {
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/* no bad return value, but ignore advice */
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return 0;
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}
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*prev = vma;
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start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
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if (end > vma->vm_end)
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end = vma->vm_end;
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end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
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force_page_cache_readahead(file->f_mapping,
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file, start, max_sane_readahead(end - start));
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return 0;
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}
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/*
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* Application no longer needs these pages. If the pages are dirty,
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* it's OK to just throw them away. The app will be more careful about
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* data it wants to keep. Be sure to free swap resources too. The
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* zap_page_range call sets things up for refill_inactive to actually free
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* these pages later if no one else has touched them in the meantime,
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* although we could add these pages to a global reuse list for
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* refill_inactive to pick up before reclaiming other pages.
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*
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* NB: This interface discards data rather than pushes it out to swap,
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* as some implementations do. This has performance implications for
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* applications like large transactional databases which want to discard
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* pages in anonymous maps after committing to backing store the data
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* that was kept in them. There is no reason to write this data out to
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* the swap area if the application is discarding it.
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*
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* An interface that causes the system to free clean pages and flush
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* dirty pages is already available as msync(MS_INVALIDATE).
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*/
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static long madvise_dontneed(struct vm_area_struct * vma,
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struct vm_area_struct ** prev,
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unsigned long start, unsigned long end)
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{
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*prev = vma;
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if (vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP))
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return -EINVAL;
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if (unlikely(vma->vm_flags & VM_NONLINEAR)) {
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struct zap_details details = {
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.nonlinear_vma = vma,
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.last_index = ULONG_MAX,
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};
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zap_page_range(vma, start, end - start, &details);
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} else
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zap_page_range(vma, start, end - start, NULL);
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return 0;
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}
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/*
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* Application wants to free up the pages and associated backing store.
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* This is effectively punching a hole into the middle of a file.
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*
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* NOTE: Currently, only shmfs/tmpfs is supported for this operation.
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* Other filesystems return -ENOSYS.
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*/
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static long madvise_remove(struct vm_area_struct *vma,
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unsigned long start, unsigned long end)
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{
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struct address_space *mapping;
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loff_t offset, endoff;
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if (vma->vm_flags & (VM_LOCKED|VM_NONLINEAR|VM_HUGETLB))
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return -EINVAL;
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if (!vma->vm_file || !vma->vm_file->f_mapping
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|| !vma->vm_file->f_mapping->host) {
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return -EINVAL;
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}
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mapping = vma->vm_file->f_mapping;
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offset = (loff_t)(start - vma->vm_start)
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+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
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endoff = (loff_t)(end - vma->vm_start - 1)
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+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
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return vmtruncate_range(mapping->host, offset, endoff);
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}
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static long
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madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
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unsigned long start, unsigned long end, int behavior)
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{
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long error;
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switch (behavior) {
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case MADV_DOFORK:
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if (vma->vm_flags & VM_IO) {
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error = -EINVAL;
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break;
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}
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case MADV_DONTFORK:
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case MADV_NORMAL:
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case MADV_SEQUENTIAL:
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case MADV_RANDOM:
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error = madvise_behavior(vma, prev, start, end, behavior);
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break;
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case MADV_REMOVE:
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error = madvise_remove(vma, start, end);
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break;
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case MADV_WILLNEED:
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error = madvise_willneed(vma, prev, start, end);
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break;
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case MADV_DONTNEED:
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error = madvise_dontneed(vma, prev, start, end);
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break;
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default:
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error = -EINVAL;
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break;
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}
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return error;
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}
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/*
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* The madvise(2) system call.
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*
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* Applications can use madvise() to advise the kernel how it should
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* handle paging I/O in this VM area. The idea is to help the kernel
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* use appropriate read-ahead and caching techniques. The information
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* provided is advisory only, and can be safely disregarded by the
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* kernel without affecting the correct operation of the application.
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*
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* behavior values:
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* MADV_NORMAL - the default behavior is to read clusters. This
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* results in some read-ahead and read-behind.
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* MADV_RANDOM - the system should read the minimum amount of data
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* on any access, since it is unlikely that the appli-
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* cation will need more than what it asks for.
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* MADV_SEQUENTIAL - pages in the given range will probably be accessed
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* once, so they can be aggressively read ahead, and
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* can be freed soon after they are accessed.
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* MADV_WILLNEED - the application is notifying the system to read
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* some pages ahead.
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* MADV_DONTNEED - the application is finished with the given range,
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* so the kernel can free resources associated with it.
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* MADV_REMOVE - the application wants to free up the given range of
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* pages and associated backing store.
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*
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* return values:
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* zero - success
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* -EINVAL - start + len < 0, start is not page-aligned,
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* "behavior" is not a valid value, or application
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* is attempting to release locked or shared pages.
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* -ENOMEM - addresses in the specified range are not currently
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* mapped, or are outside the AS of the process.
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* -EIO - an I/O error occurred while paging in data.
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* -EBADF - map exists, but area maps something that isn't a file.
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* -EAGAIN - a kernel resource was temporarily unavailable.
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*/
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asmlinkage long sys_madvise(unsigned long start, size_t len_in, int behavior)
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{
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unsigned long end, tmp;
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struct vm_area_struct * vma, *prev;
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int unmapped_error = 0;
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int error = -EINVAL;
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size_t len;
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down_write(¤t->mm->mmap_sem);
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if (start & ~PAGE_MASK)
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goto out;
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len = (len_in + ~PAGE_MASK) & PAGE_MASK;
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/* Check to see whether len was rounded up from small -ve to zero */
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if (len_in && !len)
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goto out;
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end = start + len;
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if (end < start)
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goto out;
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error = 0;
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if (end == start)
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goto out;
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/*
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* If the interval [start,end) covers some unmapped address
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* ranges, just ignore them, but return -ENOMEM at the end.
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* - different from the way of handling in mlock etc.
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*/
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vma = find_vma_prev(current->mm, start, &prev);
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if (vma && start > vma->vm_start)
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prev = vma;
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for (;;) {
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/* Still start < end. */
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error = -ENOMEM;
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if (!vma)
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goto out;
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/* Here start < (end|vma->vm_end). */
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if (start < vma->vm_start) {
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unmapped_error = -ENOMEM;
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start = vma->vm_start;
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if (start >= end)
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goto out;
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}
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/* Here vma->vm_start <= start < (end|vma->vm_end) */
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tmp = vma->vm_end;
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if (end < tmp)
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tmp = end;
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/* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
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error = madvise_vma(vma, &prev, start, tmp, behavior);
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if (error)
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goto out;
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start = tmp;
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if (start < prev->vm_end)
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start = prev->vm_end;
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error = unmapped_error;
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if (start >= end)
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goto out;
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vma = prev->vm_next;
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}
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out:
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up_write(¤t->mm->mmap_sem);
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return error;
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}
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