filemap_xip.c

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/*
 *  linux/mm/filemap_xip.c
 *
 * Copyright (C) 2005 IBM Corporation
 * Author: Carsten Otte <[email protected]>
 *
 * derived from linux/mm/filemap.c - Copyright (C) Linus Torvalds
 *
 */

#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/export.h>
#include <linux/uio.h>
#include <linux/rmap.h>
#include <linux/mmu_notifier.h>
#include <linux/sched.h>
#include <linux/seqlock.h>
#include <linux/mutex.h>
#include <linux/gfp.h>
#include <asm/tlbflush.h>
#include <asm/io.h>

/*
 * We do use our own empty page to avoid interference with other users
 * of ZERO_PAGE(), such as /dev/zero
 */
static DEFINE_MUTEX(xip_sparse_mutex);
static seqcount_t xip_sparse_seq = SEQCNT_ZERO;
static struct page *__xip_sparse_page;

/* called under xip_sparse_mutex */
static struct page *xip_sparse_page(void)
{
    if (!__xip_sparse_page) {
        struct page *page = alloc_page(GFP_HIGHUSER | __GFP_ZERO);

        if (page)
            __xip_sparse_page = page;
    }
    return __xip_sparse_page;
}

/*
 * This is a file read routine for execute in place files, and uses
 * the mapping->a_ops->get_xip_mem() function for the actual low-level
 * stuff.
 *
 * Note the struct file* is not used at all.  It may be NULL.
 */
static ssize_t
do_xip_mapping_read(struct address_space *mapping,
            struct file_ra_state *_ra,
            struct file *filp,
            char __user *buf,
            size_t len,
            loff_t *ppos)
{
    struct inode *inode = mapping->host;
    pgoff_t index, end_index;
    unsigned long offset;
    loff_t isize, pos;
    size_t copied = 0, error = 0;

    BUG_ON(!mapping->a_ops->get_xip_mem);

    pos = *ppos;
    index = pos >> PAGE_CACHE_SHIFT;
    offset = pos & ~PAGE_CACHE_MASK;

    isize = i_size_read(inode);
    if (!isize)
        goto out;

    end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
    do {
        unsigned long nr, left;
        void *xip_mem;
        unsigned long xip_pfn;
        int zero = 0;

        /* nr is the maximum number of bytes to copy from this page */
        nr = PAGE_CACHE_SIZE;
        if (index >= end_index) {
            if (index > end_index)
                goto out;
            nr = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
            if (nr <= offset) {
                goto out;
            }
        }
        nr = nr - offset;
        if (nr > len - copied)
            nr = len - copied;

        error = mapping->a_ops->get_xip_mem(mapping, index, 0,
                            &xip_mem, &xip_pfn);
        if (unlikely(error)) {
            if (error == -ENODATA) {
                /* sparse */
                zero = 1;
            } else
                goto out;
        }

        /* If users can be writing to this page using arbitrary
         * virtual addresses, take care about potential aliasing
         * before reading the page on the kernel side.
         */
        if (mapping_writably_mapped(mapping))
            /* address based flush */ ;

        /*
         * Ok, we have the mem, so now we can copy it to user space...
         *
         * The actor routine returns how many bytes were actually used..
         * NOTE! This may not be the same as how much of a user buffer
         * we filled up (we may be padding etc), so we can only update
         * "pos" here (the actor routine has to update the user buffer
         * pointers and the remaining count).
         */
        if (!zero)
            left = __copy_to_user(buf+copied, xip_mem+offset, nr);
        else
            left = __clear_user(buf + copied, nr);

        if (left) {
            error = -EFAULT;
            goto out;
        }

        copied += (nr - left);
        offset += (nr - left);
        index += offset >> PAGE_CACHE_SHIFT;
        offset &= ~PAGE_CACHE_MASK;
    } while (copied < len);

out:
    *ppos = pos + copied;
    if (filp)
        file_accessed(filp);

    return (copied ? copied : error);
}

ssize_t
xip_file_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos)
{
    if (!access_ok(VERIFY_WRITE, buf, len))
        return -EFAULT;

    return do_xip_mapping_read(filp->f_mapping, &filp->f_ra, filp,
                buf, len, ppos);
}
EXPORT_SYMBOL_GPL(xip_file_read);

/*
 * __xip_unmap is invoked from xip_unmap and
 * xip_write
 *
 * This function walks all vmas of the address_space and unmaps the
 * __xip_sparse_page when found at pgoff.
 */
static void
__xip_unmap (struct address_space * mapping,
             unsigned long pgoff)
{
    struct vm_area_struct *vma;
    struct mm_struct *mm;
    unsigned long address;
    pte_t *pte;
    pte_t pteval;
    spinlock_t *ptl;
    struct page *page;
    unsigned count;
    int locked = 0;

    count = read_seqcount_begin(&xip_sparse_seq);

    page = __xip_sparse_page;
    if (!page)
        return;

retry:
    mutex_lock(&mapping->i_mmap_mutex);
    vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
        mm = vma->vm_mm;
        address = vma->vm_start +
            ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
        BUG_ON(address < vma->vm_start || address >= vma->vm_end);
        pte = page_check_address(page, mm, address, &ptl, 1);
        if (pte) {
            /* Nuke the page table entry. */
            flush_cache_page(vma, address, pte_pfn(*pte));
            pteval = ptep_clear_flush(vma, address, pte);
            page_remove_rmap(page);
            dec_mm_counter(mm, MM_FILEPAGES);
            BUG_ON(pte_dirty(pteval));
            pte_unmap_unlock(pte, ptl);
            /* must invalidate_page _before_ freeing the page */
            mmu_notifier_invalidate_page(mm, address);
            page_cache_release(page);
        }
    }
    mutex_unlock(&mapping->i_mmap_mutex);

    if (locked) {
        mutex_unlock(&xip_sparse_mutex);
    } else if (read_seqcount_retry(&xip_sparse_seq, count)) {
        mutex_lock(&xip_sparse_mutex);
        locked = 1;
        goto retry;
    }
}

/*
 * xip_fault() is invoked via the vma operations vector for a
 * mapped memory region to read in file data during a page fault.
 *
 * This function is derived from filemap_fault, but used for execute in place
 */
static int xip_file_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
{
    struct file *file = vma->vm_file;
    struct address_space *mapping = file->f_mapping;
    struct inode *inode = mapping->host;
    pgoff_t size;
    void *xip_mem;
    unsigned long xip_pfn;
    struct page *page;
    int error;

    /* XXX: are VM_FAULT_ codes OK? */
again:
    size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
    if (vmf->pgoff >= size)
        return VM_FAULT_SIGBUS;

    error = mapping->a_ops->get_xip_mem(mapping, vmf->pgoff, 0,
                        &xip_mem, &xip_pfn);
    if (likely(!error))
        goto found;
    if (error != -ENODATA)
        return VM_FAULT_OOM;

    /* sparse block */
    if ((vma->vm_flags & (VM_WRITE | VM_MAYWRITE)) &&
        (vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) &&
        (!(mapping->host->i_sb->s_flags & MS_RDONLY))) {
        int err;

        /* maybe shared writable, allocate new block */
        mutex_lock(&xip_sparse_mutex);
        error = mapping->a_ops->get_xip_mem(mapping, vmf->pgoff, 1,
                            &xip_mem, &xip_pfn);
        mutex_unlock(&xip_sparse_mutex);
        if (error)
            return VM_FAULT_SIGBUS;
        /* unmap sparse mappings at pgoff from all other vmas */
        __xip_unmap(mapping, vmf->pgoff);

found:
        err = vm_insert_mixed(vma, (unsigned long)vmf->virtual_address,
                            xip_pfn);
        if (err == -ENOMEM)
            return VM_FAULT_OOM;
        /*
         * err == -EBUSY is fine, we've raced against another thread
         * that faulted-in the same page
         */
        if (err != -EBUSY)
            BUG_ON(err);
        return VM_FAULT_NOPAGE;
    } else {
        int err, ret = VM_FAULT_OOM;

        mutex_lock(&xip_sparse_mutex);
        write_seqcount_begin(&xip_sparse_seq);
        error = mapping->a_ops->get_xip_mem(mapping, vmf->pgoff, 0,
                            &xip_mem, &xip_pfn);
        if (unlikely(!error)) {
            write_seqcount_end(&xip_sparse_seq);
            mutex_unlock(&xip_sparse_mutex);
            goto again;
        }
        if (error != -ENODATA)
            goto out;
        /* not shared and writable, use xip_sparse_page() */
        page = xip_sparse_page();
        if (!page)
            goto out;
        err = vm_insert_page(vma, (unsigned long)vmf->virtual_address,
                            page);
        if (err == -ENOMEM)
            goto out;

        ret = VM_FAULT_NOPAGE;
out:
        write_seqcount_end(&xip_sparse_seq);
        mutex_unlock(&xip_sparse_mutex);

        return ret;
    }
}

static const struct vm_operations_struct xip_file_vm_ops = {
    .fault  = xip_file_fault,
    .page_mkwrite   = filemap_page_mkwrite,
    .remap_pages = generic_file_remap_pages,
};

int xip_file_mmap(struct file * file, struct vm_area_struct * vma)
{
    BUG_ON(!file->f_mapping->a_ops->get_xip_mem);

    file_accessed(file);
    vma->vm_ops = &xip_file_vm_ops;
    vma->vm_flags |= VM_MIXEDMAP;
    return 0;
}
EXPORT_SYMBOL_GPL(xip_file_mmap);

static ssize_t
__xip_file_write(struct file *filp, const char __user *buf,
          size_t count, loff_t pos, loff_t *ppos)
{
    struct address_space * mapping = filp->f_mapping;
    const struct address_space_operations *a_ops = mapping->a_ops;
    struct inode    *inode = mapping->host;
    long        status = 0;
    size_t      bytes;
    ssize_t     written = 0;

    BUG_ON(!mapping->a_ops->get_xip_mem);

    do {
        unsigned long index;
        unsigned long offset;
        size_t copied;
        void *xip_mem;
        unsigned long xip_pfn;

        offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
        index = pos >> PAGE_CACHE_SHIFT;
        bytes = PAGE_CACHE_SIZE - offset;
        if (bytes > count)
            bytes = count;

        status = a_ops->get_xip_mem(mapping, index, 0,
                        &xip_mem, &xip_pfn);
        if (status == -ENODATA) {
            /* we allocate a new page unmap it */
            mutex_lock(&xip_sparse_mutex);
            status = a_ops->get_xip_mem(mapping, index, 1,
                            &xip_mem, &xip_pfn);
            mutex_unlock(&xip_sparse_mutex);
            if (!status)
                /* unmap page at pgoff from all other vmas */
                __xip_unmap(mapping, index);
        }

        if (status)
            break;

        copied = bytes -
            __copy_from_user_nocache(xip_mem + offset, buf, bytes);

        if (likely(copied > 0)) {
            status = copied;

            if (status >= 0) {
                written += status;
                count -= status;
                pos += status;
                buf += status;
            }
        }
        if (unlikely(copied != bytes))
            if (status >= 0)
                status = -EFAULT;
        if (status < 0)
            break;
    } while (count);
    *ppos = pos;
    /*
     * No need to use i_size_read() here, the i_size
     * cannot change under us because we hold i_mutex.
     */
    if (pos > inode->i_size) {
        i_size_write(inode, pos);
        mark_inode_dirty(inode);
    }

    return written ? written : status;
}

ssize_t
xip_file_write(struct file *filp, const char __user *buf, size_t len,
           loff_t *ppos)
{
    struct address_space *mapping = filp->f_mapping;
    struct inode *inode = mapping->host;
    size_t count;
    loff_t pos;
    ssize_t ret;

    sb_start_write(inode->i_sb);

    mutex_lock(&inode->i_mutex);

    if (!access_ok(VERIFY_READ, buf, len)) {
        ret=-EFAULT;
        goto out_up;
    }

    pos = *ppos;
    count = len;

    /* We can write back this queue in page reclaim */
    current->backing_dev_info = mapping->backing_dev_info;

    ret = generic_write_checks(filp, &pos, &count, S_ISBLK(inode->i_mode));
    if (ret)
        goto out_backing;
    if (count == 0)
        goto out_backing;

    ret = file_remove_suid(filp);
    if (ret)
        goto out_backing;

    ret = file_update_time(filp);
    if (ret)
        goto out_backing;

    ret = __xip_file_write (filp, buf, count, pos, ppos);

 out_backing:
    current->backing_dev_info = NULL;
 out_up:
    mutex_unlock(&inode->i_mutex);
    sb_end_write(inode->i_sb);
    return ret;
}
EXPORT_SYMBOL_GPL(xip_file_write);

/*
 * truncate a page used for execute in place
 * functionality is analog to block_truncate_page but does use get_xip_mem
 * to get the page instead of page cache
 */
int
xip_truncate_page(struct address_space *mapping, loff_t from)
{
    pgoff_t index = from >> PAGE_CACHE_SHIFT;
    unsigned offset = from & (PAGE_CACHE_SIZE-1);
    unsigned blocksize;
    unsigned length;
    void *xip_mem;
    unsigned long xip_pfn;
    int err;

    BUG_ON(!mapping->a_ops->get_xip_mem);

    blocksize = 1 << mapping->host->i_blkbits;
    length = offset & (blocksize - 1);

    /* Block boundary? Nothing to do */
    if (!length)
        return 0;

    length = blocksize - length;

    err = mapping->a_ops->get_xip_mem(mapping, index, 0,
                        &xip_mem, &xip_pfn);
    if (unlikely(err)) {
        if (err == -ENODATA)
            /* Hole? No need to truncate */
            return 0;
        else
            return err;
    }
    memset(xip_mem + offset, 0, length);
    return 0;
}
EXPORT_SYMBOL_GPL(xip_truncate_page);