diff mbox series

[v9,06/10] iomap: fix iomap_dio_zero() for fs bs > system page size

Message ID 20240704112320.82104-7-kernel@pankajraghav.com (mailing list archive)
State Superseded, archived
Headers show
Series enable bs > ps in XFS | expand

Commit Message

Pankaj Raghav (Samsung) July 4, 2024, 11:23 a.m. UTC 
From: Pankaj Raghav <p.raghav@samsung.com>

iomap_dio_zero() will pad a fs block with zeroes if the direct IO size
< fs block size. iomap_dio_zero() has an implicit assumption that fs block
size < page_size. This is true for most filesystems at the moment.

If the block size > page size, this will send the contents of the page
next to zero page(as len > PAGE_SIZE) to the underlying block device,
causing FS corruption.

iomap is a generic infrastructure and it should not make any assumptions
about the fs block size and the page size of the system.

Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
---
 fs/iomap/buffered-io.c |  4 ++--
 fs/iomap/direct-io.c   | 45 ++++++++++++++++++++++++++++++++++++------
 2 files changed, 41 insertions(+), 8 deletions(-)

Comments

Hannes Reinecke July 4, 2024, 3:37 p.m. UTC | #1 
On 7/4/24 13:23, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@samsung.com>
> 
> iomap_dio_zero() will pad a fs block with zeroes if the direct IO size
> < fs block size. iomap_dio_zero() has an implicit assumption that fs block
> size < page_size. This is true for most filesystems at the moment.
> 
> If the block size > page size, this will send the contents of the page
> next to zero page(as len > PAGE_SIZE) to the underlying block device,
> causing FS corruption.
> 
> iomap is a generic infrastructure and it should not make any assumptions
> about the fs block size and the page size of the system.
> 
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> ---
>   fs/iomap/buffered-io.c |  4 ++--
>   fs/iomap/direct-io.c   | 45 ++++++++++++++++++++++++++++++++++++------
>   2 files changed, 41 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index f420c53d86acc..d745f718bcde8 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -2007,10 +2007,10 @@ iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
>   }
>   EXPORT_SYMBOL_GPL(iomap_writepages);
>   
> -static int __init iomap_init(void)
> +static int __init iomap_buffered_init(void)
>   {
>   	return bioset_init(&iomap_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE),
>   			   offsetof(struct iomap_ioend, io_bio),
>   			   BIOSET_NEED_BVECS);
>   }
> -fs_initcall(iomap_init);
> +fs_initcall(iomap_buffered_init);
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index f3b43d223a46e..c02b266bba525 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -11,6 +11,7 @@
>   #include <linux/iomap.h>
>   #include <linux/backing-dev.h>
>   #include <linux/uio.h>
> +#include <linux/set_memory.h>
>   #include <linux/task_io_accounting_ops.h>
>   #include "trace.h"
>   
> @@ -27,6 +28,13 @@
>   #define IOMAP_DIO_WRITE		(1U << 30)
>   #define IOMAP_DIO_DIRTY		(1U << 31)
>   
> +/*
> + * Used for sub block zeroing in iomap_dio_zero()
> + */
> +#define IOMAP_ZERO_PAGE_SIZE (SZ_64K)
> +#define IOMAP_ZERO_PAGE_ORDER (get_order(IOMAP_ZERO_PAGE_SIZE))
> +static struct page *zero_page;
> +

There are other users of ZERO_PAGE, most notably in fs/direct-io.c and 
block/blk-lib.c. Any chance to make this available to them?

Cheers,

Hannes
Dave Chinner July 4, 2024, 10:13 p.m. UTC | #2 
On Thu, Jul 04, 2024 at 05:37:32PM +0200, Hannes Reinecke wrote:
> On 7/4/24 13:23, Pankaj Raghav (Samsung) wrote:
> > From: Pankaj Raghav <p.raghav@samsung.com>
> > 
> > iomap_dio_zero() will pad a fs block with zeroes if the direct IO size
> > < fs block size. iomap_dio_zero() has an implicit assumption that fs block
> > size < page_size. This is true for most filesystems at the moment.
> > 
> > If the block size > page size, this will send the contents of the page
> > next to zero page(as len > PAGE_SIZE) to the underlying block device,
> > causing FS corruption.
> > 
> > iomap is a generic infrastructure and it should not make any assumptions
> > about the fs block size and the page size of the system.
> > 
> > Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> > ---
> >   fs/iomap/buffered-io.c |  4 ++--
> >   fs/iomap/direct-io.c   | 45 ++++++++++++++++++++++++++++++++++++------
> >   2 files changed, 41 insertions(+), 8 deletions(-)
> > 
> > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> > index f420c53d86acc..d745f718bcde8 100644
> > --- a/fs/iomap/buffered-io.c
> > +++ b/fs/iomap/buffered-io.c
> > @@ -2007,10 +2007,10 @@ iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
> >   }
> >   EXPORT_SYMBOL_GPL(iomap_writepages);
> > -static int __init iomap_init(void)
> > +static int __init iomap_buffered_init(void)
> >   {
> >   	return bioset_init(&iomap_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE),
> >   			   offsetof(struct iomap_ioend, io_bio),
> >   			   BIOSET_NEED_BVECS);
> >   }
> > -fs_initcall(iomap_init);
> > +fs_initcall(iomap_buffered_init);
> > diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> > index f3b43d223a46e..c02b266bba525 100644
> > --- a/fs/iomap/direct-io.c
> > +++ b/fs/iomap/direct-io.c
> > @@ -11,6 +11,7 @@
> >   #include <linux/iomap.h>
> >   #include <linux/backing-dev.h>
> >   #include <linux/uio.h>
> > +#include <linux/set_memory.h>
> >   #include <linux/task_io_accounting_ops.h>
> >   #include "trace.h"
> > @@ -27,6 +28,13 @@
> >   #define IOMAP_DIO_WRITE		(1U << 30)
> >   #define IOMAP_DIO_DIRTY		(1U << 31)
> > +/*
> > + * Used for sub block zeroing in iomap_dio_zero()
> > + */
> > +#define IOMAP_ZERO_PAGE_SIZE (SZ_64K)
> > +#define IOMAP_ZERO_PAGE_ORDER (get_order(IOMAP_ZERO_PAGE_SIZE))
> > +static struct page *zero_page;
> > +
> 
> There are other users of ZERO_PAGE, most notably in fs/direct-io.c and
> block/blk-lib.c. Any chance to make this available to them?

Please, no.

We need to stop feature creeping this patchset and bring it to a
close. If changing code entirely unrelated to this patchset is
desired, please do it as a separate independent set of patches.

-Dave.
Hannes Reinecke July 5, 2024, 6:14 a.m. UTC | #3 
On 7/5/24 00:13, Dave Chinner wrote:
> On Thu, Jul 04, 2024 at 05:37:32PM +0200, Hannes Reinecke wrote:
>> On 7/4/24 13:23, Pankaj Raghav (Samsung) wrote:
>>> From: Pankaj Raghav <p.raghav@samsung.com>
>>>
>>> iomap_dio_zero() will pad a fs block with zeroes if the direct IO size
>>> < fs block size. iomap_dio_zero() has an implicit assumption that fs block
>>> size < page_size. This is true for most filesystems at the moment.
>>>
>>> If the block size > page size, this will send the contents of the page
>>> next to zero page(as len > PAGE_SIZE) to the underlying block device,
>>> causing FS corruption.
>>>
>>> iomap is a generic infrastructure and it should not make any assumptions
>>> about the fs block size and the page size of the system.
>>>
>>> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
>>> ---
>>>    fs/iomap/buffered-io.c |  4 ++--
>>>    fs/iomap/direct-io.c   | 45 ++++++++++++++++++++++++++++++++++++------
>>>    2 files changed, 41 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
>>> index f420c53d86acc..d745f718bcde8 100644
>>> --- a/fs/iomap/buffered-io.c
>>> +++ b/fs/iomap/buffered-io.c
>>> @@ -2007,10 +2007,10 @@ iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
>>>    }
>>>    EXPORT_SYMBOL_GPL(iomap_writepages);
>>> -static int __init iomap_init(void)
>>> +static int __init iomap_buffered_init(void)
>>>    {
>>>    	return bioset_init(&iomap_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE),
>>>    			   offsetof(struct iomap_ioend, io_bio),
>>>    			   BIOSET_NEED_BVECS);
>>>    }
>>> -fs_initcall(iomap_init);
>>> +fs_initcall(iomap_buffered_init);
>>> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
>>> index f3b43d223a46e..c02b266bba525 100644
>>> --- a/fs/iomap/direct-io.c
>>> +++ b/fs/iomap/direct-io.c
>>> @@ -11,6 +11,7 @@
>>>    #include <linux/iomap.h>
>>>    #include <linux/backing-dev.h>
>>>    #include <linux/uio.h>
>>> +#include <linux/set_memory.h>
>>>    #include <linux/task_io_accounting_ops.h>
>>>    #include "trace.h"
>>> @@ -27,6 +28,13 @@
>>>    #define IOMAP_DIO_WRITE		(1U << 30)
>>>    #define IOMAP_DIO_DIRTY		(1U << 31)
>>> +/*
>>> + * Used for sub block zeroing in iomap_dio_zero()
>>> + */
>>> +#define IOMAP_ZERO_PAGE_SIZE (SZ_64K)
>>> +#define IOMAP_ZERO_PAGE_ORDER (get_order(IOMAP_ZERO_PAGE_SIZE))
>>> +static struct page *zero_page;
>>> +
>>
>> There are other users of ZERO_PAGE, most notably in fs/direct-io.c and
>> block/blk-lib.c. Any chance to make this available to them?
> 
> Please, no.
> 
> We need to stop feature creeping this patchset and bring it to a
> close. If changing code entirely unrelated to this patchset is
> desired, please do it as a separate independent set of patches.
> 
Agree; it was a suggestion only.

Pankaj, you can add my:

Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
Pankaj Raghav (Samsung) July 5, 2024, 2:19 p.m. UTC | #4 
> > > 
> > > There are other users of ZERO_PAGE, most notably in fs/direct-io.c and
> > > block/blk-lib.c. Any chance to make this available to them?
> > 
> > Please, no.
> > 
> > We need to stop feature creeping this patchset and bring it to a
> > close. If changing code entirely unrelated to this patchset is
> > desired, please do it as a separate independent set of patches.
> > 
> Agree; it was a suggestion only.

I was going to say the same thing that Dave said as well as we are 
almost there with this series :)

But I will add your suggestion in my TODO. It would be good to have some
common infra to avoid allocating larger zero pages all over the place.

> 
> Pankaj, you can add my:
> 
> Reviewed-by: Hannes Reinecke <hare@suse.de>

Thanks Hannes.
Darrick J. Wong July 8, 2024, 5:56 p.m. UTC | #5 
On Thu, Jul 04, 2024 at 11:23:16AM +0000, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@samsung.com>
> 
> iomap_dio_zero() will pad a fs block with zeroes if the direct IO size
> < fs block size. iomap_dio_zero() has an implicit assumption that fs block
> size < page_size. This is true for most filesystems at the moment.
> 
> If the block size > page size, this will send the contents of the page
> next to zero page(as len > PAGE_SIZE) to the underlying block device,
> causing FS corruption.
> 
> iomap is a generic infrastructure and it should not make any assumptions
> about the fs block size and the page size of the system.
> 
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> ---
>  fs/iomap/buffered-io.c |  4 ++--
>  fs/iomap/direct-io.c   | 45 ++++++++++++++++++++++++++++++++++++------
>  2 files changed, 41 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index f420c53d86acc..d745f718bcde8 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -2007,10 +2007,10 @@ iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
>  }
>  EXPORT_SYMBOL_GPL(iomap_writepages);
>  
> -static int __init iomap_init(void)
> +static int __init iomap_buffered_init(void)
>  {
>  	return bioset_init(&iomap_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE),
>  			   offsetof(struct iomap_ioend, io_bio),
>  			   BIOSET_NEED_BVECS);
>  }
> -fs_initcall(iomap_init);
> +fs_initcall(iomap_buffered_init);
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index f3b43d223a46e..c02b266bba525 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -11,6 +11,7 @@
>  #include <linux/iomap.h>
>  #include <linux/backing-dev.h>
>  #include <linux/uio.h>
> +#include <linux/set_memory.h>
>  #include <linux/task_io_accounting_ops.h>
>  #include "trace.h"
>  
> @@ -27,6 +28,13 @@
>  #define IOMAP_DIO_WRITE		(1U << 30)
>  #define IOMAP_DIO_DIRTY		(1U << 31)
>  
> +/*
> + * Used for sub block zeroing in iomap_dio_zero()
> + */
> +#define IOMAP_ZERO_PAGE_SIZE (SZ_64K)
> +#define IOMAP_ZERO_PAGE_ORDER (get_order(IOMAP_ZERO_PAGE_SIZE))
> +static struct page *zero_page;
> +
>  struct iomap_dio {
>  	struct kiocb		*iocb;
>  	const struct iomap_dio_ops *dops;
> @@ -232,13 +240,20 @@ void iomap_dio_bio_end_io(struct bio *bio)
>  }
>  EXPORT_SYMBOL_GPL(iomap_dio_bio_end_io);
>  
> -static void iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
> +static int iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
>  		loff_t pos, unsigned len)
>  {
>  	struct inode *inode = file_inode(dio->iocb->ki_filp);
> -	struct page *page = ZERO_PAGE(0);
>  	struct bio *bio;
>  
> +	if (!len)
> +		return 0;
> +	/*
> +	 * Max block size supported is 64k
> +	 */
> +	if (WARN_ON_ONCE(len > IOMAP_ZERO_PAGE_SIZE))
> +		return -EINVAL;
> +
>  	bio = iomap_dio_alloc_bio(iter, dio, 1, REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
>  	fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
>  				  GFP_KERNEL);
> @@ -246,8 +261,9 @@ static void iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
>  	bio->bi_private = dio;
>  	bio->bi_end_io = iomap_dio_bio_end_io;
>  
> -	__bio_add_page(bio, page, len, 0);
> +	__bio_add_page(bio, zero_page, len, 0);
>  	iomap_dio_submit_bio(iter, dio, bio, pos);
> +	return 0;
>  }
>  
>  /*
> @@ -356,8 +372,10 @@ static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
>  	if (need_zeroout) {
>  		/* zero out from the start of the block to the write offset */
>  		pad = pos & (fs_block_size - 1);
> -		if (pad)
> -			iomap_dio_zero(iter, dio, pos - pad, pad);
> +
> +		ret = iomap_dio_zero(iter, dio, pos - pad, pad);
> +		if (ret)
> +			goto out;
>  	}
>  
>  	/*
> @@ -431,7 +449,8 @@ static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
>  		/* zero out from the end of the write to the end of the block */
>  		pad = pos & (fs_block_size - 1);
>  		if (pad)
> -			iomap_dio_zero(iter, dio, pos, fs_block_size - pad);
> +			ret = iomap_dio_zero(iter, dio, pos,
> +					     fs_block_size - pad);
>  	}
>  out:
>  	/* Undo iter limitation to current extent */
> @@ -753,3 +772,17 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
>  	return iomap_dio_complete(dio);
>  }
>  EXPORT_SYMBOL_GPL(iomap_dio_rw);
> +
> +static int __init iomap_dio_init(void)
> +{
> +	zero_page = alloc_pages(GFP_KERNEL | __GFP_ZERO,
> +				IOMAP_ZERO_PAGE_ORDER);
> +
> +	if (!zero_page)
> +		return -ENOMEM;
> +
> +	set_memory_ro((unsigned long)page_address(zero_page),
> +		      1U << IOMAP_ZERO_PAGE_ORDER);
> +	return 0;
> +}
> +fs_initcall(iomap_dio_init);

This ^^^ could be refactored into a zeropage.ko module some day as a
separate patch to amortize the cost of the 64k buffer that never goes
away.

This patch looks ok though, so:
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> -- 
> 2.44.1
> 
>
Dave Chinner July 8, 2024, 10:18 p.m. UTC | #6 
On Thu, Jul 04, 2024 at 11:23:16AM +0000, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@samsung.com>
> 
> iomap_dio_zero() will pad a fs block with zeroes if the direct IO size
> < fs block size. iomap_dio_zero() has an implicit assumption that fs block
> size < page_size. This is true for most filesystems at the moment.
> 
> If the block size > page size, this will send the contents of the page
> next to zero page(as len > PAGE_SIZE) to the underlying block device,
> causing FS corruption.
> 
> iomap is a generic infrastructure and it should not make any assumptions
> about the fs block size and the page size of the system.
> 
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> ---
>  fs/iomap/buffered-io.c |  4 ++--
>  fs/iomap/direct-io.c   | 45 ++++++++++++++++++++++++++++++++++++------
>  2 files changed, 41 insertions(+), 8 deletions(-)

Looks fine.

Reviewed-by: Dave Chinner <dchinner@redhat.com>
diff mbox series

Patch

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index f420c53d86acc..d745f718bcde8 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -2007,10 +2007,10 @@  iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
 }
 EXPORT_SYMBOL_GPL(iomap_writepages);
 
-static int __init iomap_init(void)
+static int __init iomap_buffered_init(void)
 {
 	return bioset_init(&iomap_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE),
 			   offsetof(struct iomap_ioend, io_bio),
 			   BIOSET_NEED_BVECS);
 }
-fs_initcall(iomap_init);
+fs_initcall(iomap_buffered_init);
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index f3b43d223a46e..c02b266bba525 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -11,6 +11,7 @@ 
 #include <linux/iomap.h>
 #include <linux/backing-dev.h>
 #include <linux/uio.h>
+#include <linux/set_memory.h>
 #include <linux/task_io_accounting_ops.h>
 #include "trace.h"
 
@@ -27,6 +28,13 @@ 
 #define IOMAP_DIO_WRITE		(1U << 30)
 #define IOMAP_DIO_DIRTY		(1U << 31)
 
+/*
+ * Used for sub block zeroing in iomap_dio_zero()
+ */
+#define IOMAP_ZERO_PAGE_SIZE (SZ_64K)
+#define IOMAP_ZERO_PAGE_ORDER (get_order(IOMAP_ZERO_PAGE_SIZE))
+static struct page *zero_page;
+
 struct iomap_dio {
 	struct kiocb		*iocb;
 	const struct iomap_dio_ops *dops;
@@ -232,13 +240,20 @@  void iomap_dio_bio_end_io(struct bio *bio)
 }
 EXPORT_SYMBOL_GPL(iomap_dio_bio_end_io);
 
-static void iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
+static int iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
 		loff_t pos, unsigned len)
 {
 	struct inode *inode = file_inode(dio->iocb->ki_filp);
-	struct page *page = ZERO_PAGE(0);
 	struct bio *bio;
 
+	if (!len)
+		return 0;
+	/*
+	 * Max block size supported is 64k
+	 */
+	if (WARN_ON_ONCE(len > IOMAP_ZERO_PAGE_SIZE))
+		return -EINVAL;
+
 	bio = iomap_dio_alloc_bio(iter, dio, 1, REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
 	fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
 				  GFP_KERNEL);
@@ -246,8 +261,9 @@  static void iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
 	bio->bi_private = dio;
 	bio->bi_end_io = iomap_dio_bio_end_io;
 
-	__bio_add_page(bio, page, len, 0);
+	__bio_add_page(bio, zero_page, len, 0);
 	iomap_dio_submit_bio(iter, dio, bio, pos);
+	return 0;
 }
 
 /*
@@ -356,8 +372,10 @@  static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
 	if (need_zeroout) {
 		/* zero out from the start of the block to the write offset */
 		pad = pos & (fs_block_size - 1);
-		if (pad)
-			iomap_dio_zero(iter, dio, pos - pad, pad);
+
+		ret = iomap_dio_zero(iter, dio, pos - pad, pad);
+		if (ret)
+			goto out;
 	}
 
 	/*
@@ -431,7 +449,8 @@  static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
 		/* zero out from the end of the write to the end of the block */
 		pad = pos & (fs_block_size - 1);
 		if (pad)
-			iomap_dio_zero(iter, dio, pos, fs_block_size - pad);
+			ret = iomap_dio_zero(iter, dio, pos,
+					     fs_block_size - pad);
 	}
 out:
 	/* Undo iter limitation to current extent */
@@ -753,3 +772,17 @@  iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 	return iomap_dio_complete(dio);
 }
 EXPORT_SYMBOL_GPL(iomap_dio_rw);
+
+static int __init iomap_dio_init(void)
+{
+	zero_page = alloc_pages(GFP_KERNEL | __GFP_ZERO,
+				IOMAP_ZERO_PAGE_ORDER);
+
+	if (!zero_page)
+		return -ENOMEM;
+
+	set_memory_ro((unsigned long)page_address(zero_page),
+		      1U << IOMAP_ZERO_PAGE_ORDER);
+	return 0;
+}
+fs_initcall(iomap_dio_init);