[PATCH] xip: fs/mm: execute in place

- generic_file* file operations do no longer have a xip/non-xip split
- filemap_xip.c implements a new set of fops that require get_xip_page
  aop to work proper. all new fops are exported GPL-only (don't like to
  see whatever code use those except GPL modules)
- __xip_unmap now uses page_check_address, which is no longer static
  in rmap.c, and defined in linux/rmap.h
- mm/filemap.h is now much more clean, plainly having just Linus'
  inline funcs moved here from filemap.c
- fix includes in filemap_xip to make it build cleanly on i386

Signed-off-by: Carsten Otte <cotte@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

5 files changed, 680 insertions, 74 deletions

diff --git a/mm/Makefile b/mm/Makefile
index 8f70ffd..4cd69e3 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -19,3 +19,4 @@ obj-$(CONFIG_SPARSEMEM)	+= sparse.o
 obj-$(CONFIG_SHMEM) += shmem.o
 obj-$(CONFIG_TINY_SHMEM) += tiny-shmem.o
 
+obj-$(CONFIG_FS_XIP) += filemap_xip.o
diff --git a/mm/filemap.c b/mm/filemap.c
index a3598b5..7332194 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -28,6 +28,7 @@
 #include <linux/blkdev.h>
 #include <linux/security.h>
 #include <linux/syscalls.h>
+#include "filemap.h"
 /*
  * FIXME: remove all knowledge of the buffer layer from the core VM
  */
@@ -1714,32 +1715,7 @@ int remove_suid(struct dentry *dentry)
 }
 EXPORT_SYMBOL(remove_suid);
 
-/*
- * Copy as much as we can into the page and return the number of bytes which
- * were sucessfully copied.  If a fault is encountered then clear the page
- * out to (offset+bytes) and return the number of bytes which were copied.
- */
-static inline size_t
-filemap_copy_from_user(struct page *page, unsigned long offset,
-			const char __user *buf, unsigned bytes)
-{
-	char *kaddr;
-	int left;
-
-	kaddr = kmap_atomic(page, KM_USER0);
-	left = __copy_from_user_inatomic(kaddr + offset, buf, bytes);
-	kunmap_atomic(kaddr, KM_USER0);
-
-	if (left != 0) {
-		/* Do it the slow way */
-		kaddr = kmap(page);
-		left = __copy_from_user(kaddr + offset, buf, bytes);
-		kunmap(page);
-	}
-	return bytes - left;
-}
-
-static size_t
+size_t
 __filemap_copy_from_user_iovec(char *vaddr, 
 			const struct iovec *iov, size_t base, size_t bytes)
 {
@@ -1767,52 +1743,6 @@ __filemap_copy_from_user_iovec(char *vaddr,
 }
 
 /*
- * This has the same sideeffects and return value as filemap_copy_from_user().
- * The difference is that on a fault we need to memset the remainder of the
- * page (out to offset+bytes), to emulate filemap_copy_from_user()'s
- * single-segment behaviour.
- */
-static inline size_t
-filemap_copy_from_user_iovec(struct page *page, unsigned long offset,
-			const struct iovec *iov, size_t base, size_t bytes)
-{
-	char *kaddr;
-	size_t copied;
-
-	kaddr = kmap_atomic(page, KM_USER0);
-	copied = __filemap_copy_from_user_iovec(kaddr + offset, iov,
-						base, bytes);
-	kunmap_atomic(kaddr, KM_USER0);
-	if (copied != bytes) {
-		kaddr = kmap(page);
-		copied = __filemap_copy_from_user_iovec(kaddr + offset, iov,
-							base, bytes);
-		kunmap(page);
-	}
-	return copied;
-}
-
-static inline void
-filemap_set_next_iovec(const struct iovec **iovp, size_t *basep, size_t bytes)
-{
-	const struct iovec *iov = *iovp;
-	size_t base = *basep;
-
-	while (bytes) {
-		int copy = min(bytes, iov->iov_len - base);
-
-		bytes -= copy;
-		base += copy;
-		if (iov->iov_len == base) {
-			iov++;
-			base = 0;
-		}
-	}
-	*iovp = iov;
-	*basep = base;
-}
-
-/*
  * Performs necessary checks before doing a write
  *
  * Can adjust writing position aor amount of bytes to write.
diff --git a/mm/filemap.h b/mm/filemap.h
new file mode 100644
index 0000000..c2d0546
--- /dev/null
+++ b/mm/filemap.h
@@ -0,0 +1,94 @@
+/*
+ *	linux/mm/filemap.h
+ *
+ * Copyright (C) 1994-1999  Linus Torvalds
+ */
+
+#ifndef __FILEMAP_H
+#define __FILEMAP_H
+
+#include <linux/types.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/highmem.h>
+#include <linux/uio.h>
+#include <linux/config.h>
+#include <asm/uaccess.h>
+
+extern size_t
+__filemap_copy_from_user_iovec(char *vaddr,
+			       const struct iovec *iov,
+			       size_t base,
+			       size_t bytes);
+
+/*
+ * Copy as much as we can into the page and return the number of bytes which
+ * were sucessfully copied.  If a fault is encountered then clear the page
+ * out to (offset+bytes) and return the number of bytes which were copied.
+ */
+static inline size_t
+filemap_copy_from_user(struct page *page, unsigned long offset,
+			const char __user *buf, unsigned bytes)
+{
+	char *kaddr;
+	int left;
+
+	kaddr = kmap_atomic(page, KM_USER0);
+	left = __copy_from_user_inatomic(kaddr + offset, buf, bytes);
+	kunmap_atomic(kaddr, KM_USER0);
+
+	if (left != 0) {
+		/* Do it the slow way */
+		kaddr = kmap(page);
+		left = __copy_from_user(kaddr + offset, buf, bytes);
+		kunmap(page);
+	}
+	return bytes - left;
+}
+
+/*
+ * This has the same sideeffects and return value as filemap_copy_from_user().
+ * The difference is that on a fault we need to memset the remainder of the
+ * page (out to offset+bytes), to emulate filemap_copy_from_user()'s
+ * single-segment behaviour.
+ */
+static inline size_t
+filemap_copy_from_user_iovec(struct page *page, unsigned long offset,
+			const struct iovec *iov, size_t base, size_t bytes)
+{
+	char *kaddr;
+	size_t copied;
+
+	kaddr = kmap_atomic(page, KM_USER0);
+	copied = __filemap_copy_from_user_iovec(kaddr + offset, iov,
+						base, bytes);
+	kunmap_atomic(kaddr, KM_USER0);
+	if (copied != bytes) {
+		kaddr = kmap(page);
+		copied = __filemap_copy_from_user_iovec(kaddr + offset, iov,
+							base, bytes);
+		kunmap(page);
+	}
+	return copied;
+}
+
+static inline void
+filemap_set_next_iovec(const struct iovec **iovp, size_t *basep, size_t bytes)
+{
+	const struct iovec *iov = *iovp;
+	size_t base = *basep;
+
+	while (bytes) {
+		int copy = min(bytes, iov->iov_len - base);
+
+		bytes -= copy;
+		base += copy;
+		if (iov->iov_len == base) {
+			iov++;
+			base = 0;
+		}
+	}
+	*iovp = iov;
+	*basep = base;
+}
+#endif
diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c
new file mode 100644
index 0000000..7d63acd
--- /dev/null
+++ b/mm/filemap_xip.c
@@ -0,0 +1,581 @@
+/*
+ *	linux/mm/filemap_xip.c
+ *
+ * Copyright (C) 2005 IBM Corporation
+ * Author: Carsten Otte <cotte@de.ibm.com>
+ *
+ * derived from linux/mm/filemap.c - Copyright (C) Linus Torvalds
+ *
+ */
+
+#include <linux/fs.h>
+#include <linux/pagemap.h>
+#include <linux/module.h>
+#include <linux/uio.h>
+#include <linux/rmap.h>
+#include <asm/tlbflush.h>
+#include "filemap.h"
+
+/*
+ * This is a file read routine for execute in place files, and uses
+ * the mapping->a_ops->get_xip_page() function for the actual low-level
+ * stuff.
+ *
+ * Note the struct file* is not used at all.  It may be NULL.
+ */
+static void
+do_xip_mapping_read(struct address_space *mapping,
+		    struct file_ra_state *_ra,
+		    struct file *filp,
+		    loff_t *ppos,
+		    read_descriptor_t *desc,
+		    read_actor_t actor)
+{
+	struct inode *inode = mapping->host;
+	unsigned long index, end_index, offset;
+	loff_t isize;
+
+	BUG_ON(!mapping->a_ops->get_xip_page);
+
+	index = *ppos >> PAGE_CACHE_SHIFT;
+	offset = *ppos & ~PAGE_CACHE_MASK;
+
+	isize = i_size_read(inode);
+	if (!isize)
+		goto out;
+
+	end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
+	for (;;) {
+		struct page *page;
+		unsigned long nr, ret;
+
+		/* 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;
+
+		page = mapping->a_ops->get_xip_page(mapping,
+			index*(PAGE_SIZE/512), 0);
+		if (!page)
+			goto no_xip_page;
+		if (unlikely(IS_ERR(page))) {
+			if (PTR_ERR(page) == -ENODATA) {
+				/* sparse */
+				page = virt_to_page(empty_zero_page);
+			} else {
+				desc->error = PTR_ERR(page);
+				goto out;
+			}
+		} else
+			BUG_ON(!PageUptodate(page));
+
+		/* 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))
+			flush_dcache_page(page);
+
+		/*
+		 * Ok, we have the page, and it's up-to-date, 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).
+		 */
+		ret = actor(desc, page, offset, nr);
+		offset += ret;
+		index += offset >> PAGE_CACHE_SHIFT;
+		offset &= ~PAGE_CACHE_MASK;
+
+		if (ret == nr && desc->count)
+			continue;
+		goto out;
+
+no_xip_page:
+		/* Did not get the page. Report it */
+		desc->error = -EIO;
+		goto out;
+	}
+
+out:
+	*ppos = ((loff_t) index << PAGE_CACHE_SHIFT) + offset;
+	if (filp)
+		file_accessed(filp);
+}
+
+/*
+ * This is the "read()" routine for all filesystems
+ * that uses the get_xip_page address space operation.
+ */
+static ssize_t
+__xip_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
+		unsigned long nr_segs, loff_t *ppos)
+{
+	struct file *filp = iocb->ki_filp;
+	ssize_t retval;
+	unsigned long seg;
+	size_t count;
+
+	count = 0;
+	for (seg = 0; seg < nr_segs; seg++) {
+		const struct iovec *iv = &iov[seg];
+
+		/*
+		 * If any segment has a negative length, or the cumulative
+		 * length ever wraps negative then return -EINVAL.
+		 */
+		count += iv->iov_len;
+		if (unlikely((ssize_t)(count|iv->iov_len) < 0))
+			return -EINVAL;
+		if (access_ok(VERIFY_WRITE, iv->iov_base, iv->iov_len))
+			continue;
+		if (seg == 0)
+			return -EFAULT;
+		nr_segs = seg;
+		count -= iv->iov_len;	/* This segment is no good */
+		break;
+	}
+
+	retval = 0;
+	if (count) {
+		for (seg = 0; seg < nr_segs; seg++) {
+			read_descriptor_t desc;
+
+			desc.written = 0;
+			desc.arg.buf = iov[seg].iov_base;
+			desc.count = iov[seg].iov_len;
+			if (desc.count == 0)
+				continue;
+			desc.error = 0;
+			do_xip_mapping_read(filp->f_mapping, &filp->f_ra, filp,
+					    ppos, &desc, file_read_actor);
+			retval += desc.written;
+			if (!retval) {
+				retval = desc.error;
+				break;
+			}
+		}
+	}
+	return retval;
+}
+
+ssize_t
+xip_file_aio_read(struct kiocb *iocb, char __user *buf, size_t count,
+		  loff_t pos)
+{
+	struct iovec local_iov = { .iov_base = buf, .iov_len = count };
+
+	BUG_ON(iocb->ki_pos != pos);
+	return __xip_file_aio_read(iocb, &local_iov, 1, &iocb->ki_pos);
+}
+EXPORT_SYMBOL_GPL(xip_file_aio_read);
+
+ssize_t
+xip_file_readv(struct file *filp, const struct iovec *iov,
+	       unsigned long nr_segs, loff_t *ppos)
+{
+	struct kiocb kiocb;
+
+	init_sync_kiocb(&kiocb, filp);
+	return __xip_file_aio_read(&kiocb, iov, nr_segs, ppos);
+}
+EXPORT_SYMBOL_GPL(xip_file_readv);
+
+ssize_t
+xip_file_sendfile(struct file *in_file, loff_t *ppos,
+	     size_t count, read_actor_t actor, void *target)
+{
+	read_descriptor_t desc;
+
+	if (!count)
+		return 0;
+
+	desc.written = 0;
+	desc.count = count;
+	desc.arg.data = target;
+	desc.error = 0;
+
+	do_xip_mapping_read(in_file->f_mapping, &in_file->f_ra, in_file,
+			    ppos, &desc, actor);
+	if (desc.written)
+		return desc.written;
+	return desc.error;
+}
+EXPORT_SYMBOL_GPL(xip_file_sendfile);
+
+/*
+ * __xip_unmap is invoked from xip_unmap and
+ * xip_write
+ *
+ * This function walks all vmas of the address_space and unmaps the
+ * empty_zero_page when found at pgoff. Should it go in rmap.c?
+ */
+static void
+__xip_unmap (struct address_space * mapping,
+		     unsigned long pgoff)
+{
+	struct vm_area_struct *vma;
+	struct mm_struct *mm;
+	struct prio_tree_iter iter;
+	unsigned long address;
+	pte_t *pte;
+	pte_t pteval;
+
+	spin_lock(&mapping->i_mmap_lock);
+	vma_prio_tree_foreach(vma, &iter, &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);
+		/*
+		 * We need the page_table_lock to protect us from page faults,
+		 * munmap, fork, etc...
+		 */
+		pte = page_check_address(virt_to_page(empty_zero_page), mm,
+					 address);
+		if (!IS_ERR(pte)) {
+			/* Nuke the page table entry. */
+			flush_cache_page(vma, address, pte_pfn(pte));
+			pteval = ptep_clear_flush(vma, address, pte);
+			BUG_ON(pte_dirty(pteval));
+			pte_unmap(pte);
+			spin_unlock(&mm->page_table_lock);
+		}
+	}
+	spin_unlock(&mapping->i_mmap_lock);
+}
+
+/*
+ * xip_nopage() 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_nopage, but used for execute in place
+ */
+static struct page *
+xip_file_nopage(struct vm_area_struct * area,
+		   unsigned long address,
+		   int *type)
+{
+	struct file *file = area->vm_file;
+	struct address_space *mapping = file->f_mapping;
+	struct inode *inode = mapping->host;
+	struct page *page;
+	unsigned long size, pgoff, endoff;
+
+	pgoff = ((address - area->vm_start) >> PAGE_CACHE_SHIFT)
+		+ area->vm_pgoff;
+	endoff = ((area->vm_end - area->vm_start) >> PAGE_CACHE_SHIFT)
+		+ area->vm_pgoff;
+
+	size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
+	if (pgoff >= size) {
+		return NULL;
+	}
+
+	page = mapping->a_ops->get_xip_page(mapping, pgoff*(PAGE_SIZE/512), 0);
+	if (!IS_ERR(page)) {
+		BUG_ON(!PageUptodate(page));
+		return page;
+	}
+	if (PTR_ERR(page) != -ENODATA)
+		return NULL;
+
+	/* sparse block */
+	if ((area->vm_flags & (VM_WRITE | VM_MAYWRITE)) &&
+	    (area->vm_flags & (VM_SHARED| VM_MAYSHARE)) &&
+	    (!(mapping->host->i_sb->s_flags & MS_RDONLY))) {
+		/* maybe shared writable, allocate new block */
+		page = mapping->a_ops->get_xip_page (mapping,
+			pgoff*(PAGE_SIZE/512), 1);
+		if (IS_ERR(page))
+			return NULL;
+		BUG_ON(!PageUptodate(page));
+		/* unmap page at pgoff from all other vmas */
+		__xip_unmap(mapping, pgoff);
+	} else {
+		/* not shared and writable, use empty_zero_page */
+		page = virt_to_page(empty_zero_page);
+	}
+
+	return page;
+}
+
+static struct vm_operations_struct xip_file_vm_ops = {
+	.nopage         = xip_file_nopage,
+};
+
+int xip_file_mmap(struct file * file, struct vm_area_struct * vma)
+{
+	BUG_ON(!file->f_mapping->a_ops->get_xip_page);
+
+	file_accessed(file);
+	vma->vm_ops = &xip_file_vm_ops;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(xip_file_mmap);
+
+static ssize_t
+do_xip_file_write(struct kiocb *iocb, const struct iovec *iov,
+		  unsigned long nr_segs, loff_t pos, loff_t *ppos,
+		  size_t count)
+{
+	struct file *file = iocb->ki_filp;
+	struct address_space * mapping = file->f_mapping;
+	struct address_space_operations *a_ops = mapping->a_ops;
+	struct inode 	*inode = mapping->host;
+	long		status = 0;
+	struct page	*page;
+	size_t		bytes;
+	const struct iovec *cur_iov = iov; /* current iovec */
+	size_t		iov_base = 0;	   /* offset in the current iovec */
+	char __user	*buf;
+	ssize_t		written = 0;
+
+	BUG_ON(!mapping->a_ops->get_xip_page);
+
+	buf = iov->iov_base;
+	do {
+		unsigned long index;
+		unsigned long offset;
+		size_t copied;
+
+		offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
+		index = pos >> PAGE_CACHE_SHIFT;
+		bytes = PAGE_CACHE_SIZE - offset;
+		if (bytes > count)
+			bytes = count;
+
+		/*
+		 * Bring in the user page that we will copy from _first_.
+		 * Otherwise there's a nasty deadlock on copying from the
+		 * same page as we're writing to, without it being marked
+		 * up-to-date.
+		 */
+		fault_in_pages_readable(buf, bytes);
+
+		page = a_ops->get_xip_page(mapping,
+						    index*(PAGE_SIZE/512), 0);
+		if (IS_ERR(page) && (PTR_ERR(page) == -ENODATA)) {
+			/* we allocate a new page unmap it */
+			page = a_ops->get_xip_page(mapping,
+				index*(PAGE_SIZE/512), 1);
+			if (!IS_ERR(page))
+			/* unmap page at pgoff from all other vmas */
+			__xip_unmap(mapping, index);
+
+		}
+
+		if (IS_ERR(page)) {
+			status = PTR_ERR(page);
+			break;
+		}
+
+		BUG_ON(!PageUptodate(page));
+
+		if (likely(nr_segs == 1))
+			copied = filemap_copy_from_user(page, offset,
+							buf, bytes);
+		else
+			copied = filemap_copy_from_user_iovec(page, offset,
+						cur_iov, iov_base, bytes);
+		flush_dcache_page(page);
+		if (likely(copied > 0)) {
+			status = copied;
+
+			if (status >= 0) {
+				written += status;
+				count -= status;
+				pos += status;
+				buf += status;
+				if (unlikely(nr_segs > 1))
+					filemap_set_next_iovec(&cur_iov,
+							&iov_base, 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_sem.
+	 */
+	if (pos > inode->i_size) {
+		i_size_write(inode, pos);
+		mark_inode_dirty(inode);
+	}
+
+	return written ? written : status;
+}
+
+static ssize_t
+xip_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov,
+				unsigned long nr_segs, loff_t *ppos)
+{
+	struct file *file = iocb->ki_filp;
+	struct address_space * mapping = file->f_mapping;
+	size_t ocount;		/* original count */
+	size_t count;		/* after file limit checks */
+	struct inode 	*inode = mapping->host;
+	unsigned long	seg;
+	loff_t		pos;
+	ssize_t		written;
+	ssize_t		err;
+
+	ocount = 0;
+	for (seg = 0; seg < nr_segs; seg++) {
+		const struct iovec *iv = &iov[seg];
+
+		/*
+		 * If any segment has a negative length, or the cumulative
+		 * length ever wraps negative then return -EINVAL.
+		 */
+		ocount += iv->iov_len;
+		if (unlikely((ssize_t)(ocount|iv->iov_len) < 0))
+			return -EINVAL;
+		if (access_ok(VERIFY_READ, iv->iov_base, iv->iov_len))
+			continue;
+		if (seg == 0)
+			return -EFAULT;
+		nr_segs = seg;
+		ocount -= iv->iov_len;	/* This segment is no good */
+		break;
+	}
+
+	count = ocount;
+	pos = *ppos;
+
+	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
+
+	written = 0;
+
+	err = generic_write_checks(file, &pos, &count, S_ISBLK(inode->i_mode));
+	if (err)
+		goto out;
+
+	if (count == 0)
+		goto out;
+
+	err = remove_suid(file->f_dentry);
+	if (err)
+		goto out;
+
+	inode_update_time(inode, 1);
+
+	/* use execute in place to copy directly to disk */
+	written = do_xip_file_write (iocb, iov,
+				  nr_segs, pos, ppos, count);
+ out:
+	return written ? written : err;
+}
+
+static ssize_t
+__xip_file_write_nolock(struct file *file, const struct iovec *iov,
+			unsigned long nr_segs, loff_t *ppos)
+{
+	struct kiocb kiocb;
+
+	init_sync_kiocb(&kiocb, file);
+	return xip_file_aio_write_nolock(&kiocb, iov, nr_segs, ppos);
+}
+
+ssize_t
+xip_file_aio_write(struct kiocb *iocb, const char __user *buf,
+		       size_t count, loff_t pos)
+{
+	struct file *file = iocb->ki_filp;
+	struct address_space *mapping = file->f_mapping;
+	struct inode *inode = mapping->host;
+	ssize_t ret;
+	struct iovec local_iov = { .iov_base = (void __user *)buf,
+				   .iov_len = count };
+
+	BUG_ON(iocb->ki_pos != pos);
+
+	down(&inode->i_sem);
+	ret = xip_file_aio_write_nolock(iocb, &local_iov, 1, &iocb->ki_pos);
+	up(&inode->i_sem);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(xip_file_aio_write);
+
+ssize_t xip_file_writev(struct file *file, const struct iovec *iov,
+			unsigned long nr_segs, loff_t *ppos)
+{
+	struct address_space *mapping = file->f_mapping;
+	struct inode *inode = mapping->host;
+	ssize_t ret;
+
+	down(&inode->i_sem);
+	ret = __xip_file_write_nolock(file, iov, nr_segs, ppos);
+	up(&inode->i_sem);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(xip_file_writev);
+
+/*
+ * truncate a page used for execute in place
+ * functionality is analog to block_truncate_page but does use get_xip_page
+ * 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;
+	struct page *page;
+	void *kaddr;
+	int err;
+
+	BUG_ON(!mapping->a_ops->get_xip_page);
+
+	blocksize = 1 << mapping->host->i_blkbits;
+	length = offset & (blocksize - 1);
+
+	/* Block boundary? Nothing to do */
+	if (!length)
+		return 0;
+
+	length = blocksize - length;
+
+	page = mapping->a_ops->get_xip_page(mapping,
+					    index*(PAGE_SIZE/512), 0);
+	err = -ENOMEM;
+	if (!page)
+		goto out;
+	if (unlikely(IS_ERR(page))) {
+		if (PTR_ERR(page) == -ENODATA) {
+			/* Hole? No need to truncate */
+			return 0;
+		} else {
+			err = PTR_ERR(page);
+			goto out;
+		}
+	} else
+		BUG_ON(!PageUptodate(page));
+	kaddr = kmap_atomic(page, KM_USER0);
+	memset(kaddr + offset, 0, length);
+	kunmap_atomic(kaddr, KM_USER0);
+
+	flush_dcache_page(page);
+	err = 0;
+out:
+	return err;
+}
+EXPORT_SYMBOL_GPL(xip_truncate_page);
diff --git a/mm/rmap.c b/mm/rmap.c
index 89770bd..08ac5c7 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -247,8 +247,8 @@ unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
  *
  * On success returns with mapped pte and locked mm->page_table_lock.
  */
-static pte_t *page_check_address(struct page *page, struct mm_struct *mm,
-					unsigned long address)
+pte_t *page_check_address(struct page *page, struct mm_struct *mm,
+			  unsigned long address)
 {
 	pgd_t *pgd;
 	pud_t *pud;