[rfc][patch 2/2] xip: support non-struct page memory

[Nick Piggin <npiggin@suse.de>]

This is just a prototype for one possible way of supporting this. I may
be missing some important detail or eg. have missed some requirement of the
s390 XIP block device that makes the idea infeasible... comments?

---

Convert XIP to support non-struct page backed memory, using VM_MIXEDMAP
for the user mappings.

This requires the get_xip_page API to be changed to an address based one.

(The kaddr->pfn conversion may not be quite right for all architectures or XIP
memory mappings, and the cacheflushing may need to be updated for some archs). 

Index: linux-2.6/fs/ext2/inode.c
===================================================================
--- linux-2.6.orig/fs/ext2/inode.c
+++ linux-2.6/fs/ext2/inode.c
@@ -800,7 +800,7 @@ const struct address_space_operations ex
 
 const struct address_space_operations ext2_aops_xip = {
 	.bmap			= ext2_bmap,
-	.get_xip_page		= ext2_get_xip_page,
+	.get_xip_address	= ext2_get_xip_address,
 };
 
 const struct address_space_operations ext2_nobh_aops = {
Index: linux-2.6/fs/ext2/xip.c
===================================================================
--- linux-2.6.orig/fs/ext2/xip.c
+++ linux-2.6/fs/ext2/xip.c
@@ -15,24 +15,25 @@
 #include "xip.h"
 
 static inline int
-__inode_direct_access(struct inode *inode, sector_t sector,
-		      unsigned long *data)
+__inode_direct_access(struct inode *inode, sector_t block, unsigned long *data)
 {
+	sector_t sector;
 	BUG_ON(!inode->i_sb->s_bdev->bd_disk->fops->direct_access);
+
+	sector = block * (PAGE_SIZE / 512); /* ext2 block to bdev sector */
 	return inode->i_sb->s_bdev->bd_disk->fops
-		->direct_access(inode->i_sb->s_bdev,sector,data);
+		->direct_access(inode->i_sb->s_bdev, sector, data);
 }
 
 static inline int
-__ext2_get_sector(struct inode *inode, sector_t offset, int create,
+__ext2_get_block(struct inode *inode, pgoff_t pgoff, int create,
 		   sector_t *result)
 {
 	struct buffer_head tmp;
 	int rc;
 
 	memset(&tmp, 0, sizeof(struct buffer_head));
-	rc = ext2_get_block(inode, offset/ (PAGE_SIZE/512), &tmp,
-			    create);
+	rc = ext2_get_block(inode, pgoff, &tmp, create);
 	*result = tmp.b_blocknr;
 
 	/* did we get a sparse block (hole in the file)? */
@@ -45,13 +46,12 @@ __ext2_get_sector(struct inode *inode, s
 }
 
 int
-ext2_clear_xip_target(struct inode *inode, int block)
+ext2_clear_xip_target(struct inode *inode, sector_t block)
 {
-	sector_t sector = block * (PAGE_SIZE/512);
 	unsigned long data;
 	int rc;
 
-	rc = __inode_direct_access(inode, sector, &data);
+	rc = __inode_direct_access(inode, block, &data);
 	if (!rc)
 		clear_page((void*)data);
 	return rc;
@@ -69,24 +69,24 @@ void ext2_xip_verify_sb(struct super_blo
 	}
 }
 
-struct page *
-ext2_get_xip_page(struct address_space *mapping, sector_t offset,
-		   int create)
+void *
+ext2_get_xip_address(struct address_space *mapping, pgoff_t pgoff, int create)
 {
 	int rc;
 	unsigned long data;
-	sector_t sector;
+	sector_t block;
 
 	/* first, retrieve the sector number */
-	rc = __ext2_get_sector(mapping->host, offset, create, &sector);
+	rc = __ext2_get_block(mapping->host, pgoff, create, &block);
 	if (rc)
 		goto error;
 
 	/* retrieve address of the target data */
-	rc = __inode_direct_access
-		(mapping->host, sector * (PAGE_SIZE/512), &data);
-	if (!rc)
-		return virt_to_page(data);
+	rc = __inode_direct_access(mapping->host, block, &data);
+	if (rc)
+		goto error;
+
+	return (void *)data;
 
  error:
 	return ERR_PTR(rc);
Index: linux-2.6/fs/ext2/xip.h
===================================================================
--- linux-2.6.orig/fs/ext2/xip.h
+++ linux-2.6/fs/ext2/xip.h
@@ -7,15 +7,15 @@
 
 #ifdef CONFIG_EXT2_FS_XIP
 extern void ext2_xip_verify_sb (struct super_block *);
-extern int ext2_clear_xip_target (struct inode *, int);
+extern int ext2_clear_xip_target (struct inode *, sector_t);
 
 static inline int ext2_use_xip (struct super_block *sb)
 {
 	struct ext2_sb_info *sbi = EXT2_SB(sb);
 	return (sbi->s_mount_opt & EXT2_MOUNT_XIP);
 }
-struct page* ext2_get_xip_page (struct address_space *, sector_t, int);
-#define mapping_is_xip(map) unlikely(map->a_ops->get_xip_page)
+void *ext2_get_xip_address(struct address_space *, sector_t, int);
+#define mapping_is_xip(map) unlikely(map->a_ops->get_xip_address)
 #else
 #define mapping_is_xip(map)			0
 #define ext2_xip_verify_sb(sb)			do { } while (0)
Index: linux-2.6/fs/open.c
===================================================================
--- linux-2.6.orig/fs/open.c
+++ linux-2.6/fs/open.c
@@ -778,7 +778,7 @@ static struct file *__dentry_open(struct
 	if (f->f_flags & O_DIRECT) {
 		if (!f->f_mapping->a_ops ||
 		    ((!f->f_mapping->a_ops->direct_IO) &&
-		    (!f->f_mapping->a_ops->get_xip_page))) {
+		    (!f->f_mapping->a_ops->get_xip_address))) {
 			fput(f);
 			f = ERR_PTR(-EINVAL);
 		}
Index: linux-2.6/include/linux/fs.h
===================================================================
--- linux-2.6.orig/include/linux/fs.h
+++ linux-2.6/include/linux/fs.h
@@ -473,8 +473,7 @@ struct address_space_operations {
 	int (*releasepage) (struct page *, gfp_t);
 	ssize_t (*direct_IO)(int, struct kiocb *, const struct iovec *iov,
 			loff_t offset, unsigned long nr_segs);
-	struct page* (*get_xip_page)(struct address_space *, sector_t,
-			int);
+	void * (*get_xip_address)(struct address_space *, pgoff_t, int);
 	/* migrate the contents of a page to the specified target */
 	int (*migratepage) (struct address_space *,
 			struct page *, struct page *);
Index: linux-2.6/mm/fadvise.c
===================================================================
--- linux-2.6.orig/mm/fadvise.c
+++ linux-2.6/mm/fadvise.c
@@ -49,7 +49,7 @@ asmlinkage long sys_fadvise64_64(int fd,
 		goto out;
 	}
 
-	if (mapping->a_ops->get_xip_page)
+	if (mapping->a_ops->get_xip_address)
 		/* no bad return value, but ignore advice */
 		goto out;
 
Index: linux-2.6/mm/filemap_xip.c
===================================================================
--- linux-2.6.orig/mm/filemap_xip.c
+++ linux-2.6/mm/filemap_xip.c
@@ -15,6 +15,7 @@
 #include <linux/rmap.h>
 #include <linux/sched.h>
 #include <asm/tlbflush.h>
+#include <asm/io.h>
 
 /*
  * We do use our own empty page to avoid interference with other users
@@ -41,36 +42,39 @@ static struct page *xip_sparse_page(void
 
 /*
  * 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
+ * the mapping->a_ops->get_xip_address() function for the actual low-level
  * stuff.
  *
  * Note the struct file* is not used at all.  It may be NULL.
  */
-static void
+static ssize_t
 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)
+		    char __user *buf,
+		    size_t len,
+		    loff_t *ppos)
 {
 	struct inode *inode = mapping->host;
 	unsigned long index, end_index, offset;
-	loff_t isize;
+	loff_t isize, pos;
+	size_t copied = 0, error = 0;
 
-	BUG_ON(!mapping->a_ops->get_xip_page);
+	BUG_ON(!mapping->a_ops->get_xip_address);
 
-	index = *ppos >> PAGE_CACHE_SHIFT;
-	offset = *ppos & ~PAGE_CACHE_MASK;
+	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;
-	for (;;) {
-		struct page *page;
-		unsigned long nr, ret;
+	do {
+		unsigned long nr, left;
+		void *xip_mem;
+		int zero = 0;
 
 		/* nr is the maximum number of bytes to copy from this page */
 		nr = PAGE_CACHE_SIZE;
@@ -83,17 +87,20 @@ do_xip_mapping_read(struct address_space
 			}
 		}
 		nr = nr - offset;
+		if (nr > len)
+			nr = len;
 
-		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) {
+		xip_mem = mapping->a_ops->get_xip_address(mapping, index, 0);
+		if (!xip_mem) {
+			error = -EIO;
+			goto out;
+		}
+		if (unlikely(IS_ERR(xip_mem))) {
+			if (PTR_ERR(xip_mem) == -ENODATA) {
 				/* sparse */
-				page = ZERO_PAGE(0);
+				zero = 1;
 			} else {
-				desc->error = PTR_ERR(page);
+				error = PTR_ERR(xip_mem);
 				goto out;
 			}
 		}
@@ -103,10 +110,10 @@ do_xip_mapping_read(struct address_space
 		 * before reading the page on the kernel side.
 		 */
 		if (mapping_writably_mapped(mapping))
-			flush_dcache_page(page);
+			/* address based flush */ ;
 
 		/*
-		 * Ok, we have the page, so now we can copy it to user space...
+		 * 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
@@ -114,47 +121,38 @@ do_xip_mapping_read(struct address_space
 		 * "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 (!zero)
+			left = __copy_to_user(buf+copied, xip_mem+offset, nr);
+		else
+			left = __clear_user(buf + copied, nr);
 
-		if (ret == nr && desc->count)
-			continue;
-		goto out;
+		if (left) {
+			error = -EFAULT;
+			goto out;
+		}
 
-no_xip_page:
-		/* Did not get the page. Report it */
-		desc->error = -EIO;
-		goto out;
-	}
+		copied += (nr - left);
+		offset += (nr - left);
+		index += offset >> PAGE_CACHE_SHIFT;
+		offset &= ~PAGE_CACHE_MASK;
+	} while (copied < len);
 
 out:
-	*ppos = ((loff_t) index << PAGE_CACHE_SHIFT) + offset;
+	*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)
 {
-	read_descriptor_t desc;
-
 	if (!access_ok(VERIFY_WRITE, buf, len))
 		return -EFAULT;
 
-	desc.written = 0;
-	desc.arg.buf = buf;
-	desc.count = len;
-	desc.error = 0;
-
-	do_xip_mapping_read(filp->f_mapping, &filp->f_ra, filp,
-			    ppos, &desc, file_read_actor);
-
-	if (desc.written)
-		return desc.written;
-	else
-		return desc.error;
+	return do_xip_mapping_read(filp->f_mapping, &filp->f_ra, filp,
+			    buf, len, ppos);
 }
 EXPORT_SYMBOL_GPL(xip_file_read);
 
@@ -209,13 +207,14 @@ __xip_unmap (struct address_space * mapp
  *
  * This function is derived from filemap_fault, but used for execute in place
  */
-static int xip_file_fault(struct vm_area_struct *area, struct vm_fault *vmf)
+static int xip_file_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
-	struct file *file = area->vm_file;
+	struct file *file = vma->vm_file;
 	struct address_space *mapping = file->f_mapping;
 	struct inode *inode = mapping->host;
-	struct page *page;
 	pgoff_t size;
+	void *xip_mem;
+	struct page *page;
 
 	/* XXX: are VM_FAULT_ codes OK? */
 
@@ -223,24 +222,32 @@ static int xip_file_fault(struct vm_area
 	if (vmf->pgoff >= size)
 		return VM_FAULT_SIGBUS;
 
-	page = mapping->a_ops->get_xip_page(mapping,
-					vmf->pgoff*(PAGE_SIZE/512), 0);
-	if (!IS_ERR(page))
-		goto out;
-	if (PTR_ERR(page) != -ENODATA)
+	xip_mem = mapping->a_ops->get_xip_address(mapping, vmf->pgoff, 0);
+	if (!IS_ERR(xip_mem))
+		goto found;
+	if (PTR_ERR(xip_mem) != -ENODATA)
 		return VM_FAULT_OOM;
 
 	/* sparse block */
-	if ((area->vm_flags & (VM_WRITE | VM_MAYWRITE)) &&
-	    (area->vm_flags & (VM_SHARED| VM_MAYSHARE)) &&
+	if ((vma->vm_flags & (VM_WRITE | VM_MAYWRITE)) &&
+	    (vma->vm_flags & (VM_SHARED| VM_MAYSHARE)) &&
 	    (!(mapping->host->i_sb->s_flags & MS_RDONLY))) {
+		unsigned long pfn;
+
 		/* maybe shared writable, allocate new block */
-		page = mapping->a_ops->get_xip_page(mapping,
-					vmf->pgoff*(PAGE_SIZE/512), 1);
-		if (IS_ERR(page))
+		xip_mem = mapping->a_ops->get_xip_address(mapping,vmf->pgoff,1);
+		if (IS_ERR(xip_mem))
 			return VM_FAULT_SIGBUS;
-		/* unmap page at pgoff from all other vmas */
+		/* unmap sparse mappings at pgoff from all other vmas */
 		__xip_unmap(mapping, vmf->pgoff);
+
+found:
+		pfn = virt_to_phys(xip_mem) >> PAGE_SHIFT;
+		if (!pfn_valid(pfn)) {
+			vm_insert_pfn(vma, (unsigned long)vmf->virtual_address, pfn);
+			return VM_FAULT_NOPAGE;
+		}
+		page = pfn_to_page(pfn);
 	} else {
 		/* not shared and writable, use xip_sparse_page() */
 		page = xip_sparse_page();
@@ -248,7 +255,6 @@ static int xip_file_fault(struct vm_area
 			return VM_FAULT_OOM;
 	}
 
-out:
 	page_cache_get(page);
 	vmf->page = page;
 	return 0;
@@ -260,11 +266,11 @@ static struct vm_operations_struct xip_f
 
 int xip_file_mmap(struct file * file, struct vm_area_struct * vma)
 {
-	BUG_ON(!file->f_mapping->a_ops->get_xip_page);
+	BUG_ON(!file->f_mapping->a_ops->get_xip_address);
 
 	file_accessed(file);
 	vma->vm_ops = &xip_file_vm_ops;
-	vma->vm_flags |= VM_CAN_NONLINEAR;
+	vma->vm_flags |= VM_CAN_NONLINEAR | VM_MIXEDMAP;
 	return 0;
 }
 EXPORT_SYMBOL_GPL(xip_file_mmap);
@@ -277,17 +283,16 @@ __xip_file_write(struct file *filp, cons
 	const struct address_space_operations *a_ops = mapping->a_ops;
 	struct inode 	*inode = mapping->host;
 	long		status = 0;
-	struct page	*page;
 	size_t		bytes;
 	ssize_t		written = 0;
 
-	BUG_ON(!mapping->a_ops->get_xip_page);
+	BUG_ON(!mapping->a_ops->get_xip_address);
 
 	do {
 		unsigned long index;
 		unsigned long offset;
 		size_t copied;
-		char *kaddr;
+		void *xip_mem;
 
 		offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
 		index = pos >> PAGE_CACHE_SHIFT;
@@ -295,28 +300,22 @@ __xip_file_write(struct file *filp, cons
 		if (bytes > count)
 			bytes = count;
 
-		page = a_ops->get_xip_page(mapping,
-					   index*(PAGE_SIZE/512), 0);
-		if (IS_ERR(page) && (PTR_ERR(page) == -ENODATA)) {
+		xip_mem = a_ops->get_xip_address(mapping, index, 0);
+		if (IS_ERR(xip_mem) && (PTR_ERR(xip_mem) == -ENODATA)) {
 			/* we allocate a new page unmap it */
-			page = a_ops->get_xip_page(mapping,
-						   index*(PAGE_SIZE/512), 1);
-			if (!IS_ERR(page))
+			xip_mem = a_ops->get_xip_address(mapping, index, 1);
+			if (!IS_ERR(xip_mem))
 				/* unmap page at pgoff from all other vmas */
 				__xip_unmap(mapping, index);
 		}
 
-		if (IS_ERR(page)) {
-			status = PTR_ERR(page);
+		if (IS_ERR(xip_mem)) {
+			status = PTR_ERR(xip_mem);
 			break;
 		}
 
-		fault_in_pages_readable(buf, bytes);
-		kaddr = kmap_atomic(page, KM_USER0);
 		copied = bytes -
-			__copy_from_user_inatomic_nocache(kaddr + offset, buf, bytes);
-		kunmap_atomic(kaddr, KM_USER0);
-		flush_dcache_page(page);
+			__copy_from_user_nocache(xip_mem + offset, buf, bytes);
 
 		if (likely(copied > 0)) {
 			status = copied;
@@ -396,7 +395,7 @@ 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_page
+ * functionality is analog to block_truncate_page but does use get_xip_adddress
  * to get the page instead of page cache
  */
 int
@@ -406,9 +405,9 @@ xip_truncate_page(struct address_space *
 	unsigned offset = from & (PAGE_CACHE_SIZE-1);
 	unsigned blocksize;
 	unsigned length;
-	struct page *page;
+	void *xip_mem;
 
-	BUG_ON(!mapping->a_ops->get_xip_page);
+	BUG_ON(!mapping->a_ops->get_xip_address);
 
 	blocksize = 1 << mapping->host->i_blkbits;
 	length = offset & (blocksize - 1);
@@ -419,18 +418,17 @@ xip_truncate_page(struct address_space *
 
 	length = blocksize - length;
 
-	page = mapping->a_ops->get_xip_page(mapping,
-					    index*(PAGE_SIZE/512), 0);
-	if (!page)
+	xip_mem = mapping->a_ops->get_xip_address(mapping, index, 0);
+	if (!xip_mem)
 		return -ENOMEM;
-	if (unlikely(IS_ERR(page))) {
-		if (PTR_ERR(page) == -ENODATA)
+	if (unlikely(IS_ERR(xip_mem))) {
+		if (PTR_ERR(xip_mem) == -ENODATA)
 			/* Hole? No need to truncate */
 			return 0;
 		else
-			return PTR_ERR(page);
+			return PTR_ERR(xip_mem);
 	}
-	zero_user_page(page, offset, length, KM_USER0);
+	memset(xip_mem + offset, 0, length);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(xip_truncate_page);
Index: linux-2.6/mm/madvise.c
===================================================================
--- linux-2.6.orig/mm/madvise.c
+++ linux-2.6/mm/madvise.c
@@ -112,7 +112,7 @@ static long madvise_willneed(struct vm_a
 	if (!file)
 		return -EBADF;
 
-	if (file->f_mapping->a_ops->get_xip_page) {
+	if (file->f_mapping->a_ops->get_xip_address) {
 		/* no bad return value, but ignore advice */
 		return 0;
 	}

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