[PATCH v5 0/9] Use vm_insert_range

[PATCH v5 0/9] Use vm_insert_range

[Souptick Joarder]

v1 -> v2:
        Address review comment on mm/memory.c. Add EXPORT_SYMBOL
        for vm_insert_range and corrected the documentation part
        for this API.

        In drivers/gpu/drm/xen/xen_drm_front_gem.c, replace err
        with ret as suggested.

        In drivers/iommu/dma-iommu.c, handle the scenario of partial
        mmap() of large buffer by passing *pages + vma->vm_pgoff* to
        vm_insert_range().

v2 -> v3:
        Declaration of vm_insert_range() moved to include/linux/mm.h

v3 -> v4:
	Address review comments.

	In mm/memory.c. Added error check.

	In arch/arm/mm/dma-mapping.c, remove part of error check as the
	similar is checked inside vm_insert_range.

	In rockchip/rockchip_drm_gem.c, vma->vm_pgoff is respected as
	this might be passed as non zero value considering partial
	mapping of large buffer.

	In iommu/dma-iommu.c, count is modifed as (count - vma->vm_pgoff)
	to handle partial mapping scenario in v2.

v4 -> v5:
	Address review comment on [2/9] and [4/9]

	In arch/arm/mm/dma-mapping.c, added the error check which was removed
	in v4, as without those error check we might end up overrun the page
	array.

	In rockchip/rockchip_drm_gem.c, added error check which was removed in
	v1, as without this it might overrun page array. Adjusted page_count
	parameter before passing it to vm_insert_range().

Souptick Joarder (9):
  mm: Introduce new vm_insert_range API
  arch/arm/mm/dma-mapping.c: Convert to use vm_insert_range
  drivers/firewire/core-iso.c: Convert to use vm_insert_range
  drm/rockchip/rockchip_drm_gem.c: Convert to use vm_insert_range
  drm/xen/xen_drm_front_gem.c: Convert to use vm_insert_range
  iommu/dma-iommu.c: Convert to use vm_insert_range
  videobuf2/videobuf2-dma-sg.c: Convert to use vm_insert_range
  xen/gntdev.c: Convert to use vm_insert_range
  xen/privcmd-buf.c: Convert to use vm_insert_range

 arch/arm/mm/dma-mapping.c                         | 18 ++++------
 drivers/firewire/core-iso.c                       | 15 ++-------
 drivers/gpu/drm/rockchip/rockchip_drm_gem.c       | 14 ++------
 drivers/gpu/drm/xen/xen_drm_front_gem.c           | 20 ++++-------
 drivers/iommu/dma-iommu.c                         | 13 ++-----
 drivers/media/common/videobuf2/videobuf2-dma-sg.c | 23 ++++---------
 drivers/xen/gntdev.c                              | 11 +++---
 drivers/xen/privcmd-buf.c                         |  8 ++---
 include/linux/mm.h                                |  2 ++
 mm/memory.c                                       | 41 +++++++++++++++++++++++
 mm/nommu.c                                        |  7 ++++
 11 files changed, 83 insertions(+), 89 deletions(-)

-- 
1.9.1

Re: [PATCH v5 0/9] Use vm_insert_range

[Russell King - ARM Linux]

Having discussed with Matthew offlist, I think we've come to the
following conclusion - there's a number of drivers that buggily
ignore vm_pgoff.

So, what I proposed is:

static int __vm_insert_range(struct vm_struct *vma, struct page *pages,
			     size_t num, unsigned long offset)
{
	unsigned long count = vma_pages(vma);
	unsigned long uaddr = vma->vm_start;
	int ret;

	/* Fail if the user requested offset is beyond the end of the object */
	if (offset > num)
		return -ENXIO;

	/* Fail if the user requested size exceeds available object size */
	if (count > num - offset)
		return -ENXIO;

	/* Never exceed the number of pages that the user requested */
	for (i = 0; i < count; i++) {
		ret = vm_insert_page(vma, uaddr, pages[offset + i]);
		if (ret < 0)
			return ret;
		uaddr += PAGE_SIZE;
	}

	return 0;
}

/*
 * Maps an object consisting of `num' `pages', catering for the user's
 * requested vm_pgoff
 */
int vm_insert_range(struct vm_struct *vma, struct page *pages, size_t num)
{
	return __vm_insert_range(vma, pages, num, vma->vm_pgoff);
}

/*
 * Maps a set of pages, always starting at page[0]
 */
int vm_insert_range_buggy(struct vm_struct *vma, struct page *pages, size_t num)
{
	return __vm_insert_range(vma, pages, num, 0);
}

With this, drivers such as iommu/dma-iommu.c can be converted thusly:

 int iommu_dma_mmap(struct page **pages, size_t size, struct vm_area_struct *vma+)
 {
-	unsigned long uaddr = vma->vm_start;
-	unsigned int i, count = PAGE_ALIGN(size) >> PAGE_SHIFT;
-	int ret = -ENXIO;
-
-	for (i = vma->vm_pgoff; i < count && uaddr < vma->vm_end; i++) {
-		ret = vm_insert_page(vma, uaddr, pages[i]);
-		if (ret)
-			break;
-		uaddr += PAGE_SIZE;
-	}
-	return ret;
+	return vm_insert_range(vma, pages, PAGE_ALIGN(size) >> PAGE_SHIFT);
}

and drivers such as firewire/core-iso.c:

 int fw_iso_buffer_map_vma(struct fw_iso_buffer *buffer,
 			  struct vm_area_struct *vma)
 {
-	unsigned long uaddr;
-	int i, err;
-
-	uaddr = vma->vm_start;
-	for (i = 0; i < buffer->page_count; i++) {
-		err = vm_insert_page(vma, uaddr, buffer->pages[i]);
-		if (err)
-			return err;
-
-		uaddr += PAGE_SIZE;
-	}
-
-	return 0;
+	return vm_insert_range_buggy(vma, buffer->pages, buffer->page_count);
}

and this gives us something to grep for to find these buggy drivers.

Now, this may not look exactly equivalent, but if you look at
fw_device_op_mmap(), buffer->page_count is basically vma_pages(vma)
at this point, which means this should be equivalent.

We _could_ then at a later date "fix" these drivers to behave according
to the normal vm_pgoff offsetting simply by removing the _buggy suffix
on the function name... and if that causes regressions, it gives us an
easy way to revert (as long as vm_insert_range_buggy() remains
available.)

In the case of firewire/core-iso.c, it currently ignores the mmap offset
entirely, so making the above suggested change would be tantamount to
causing it to return -ENXIO for any non-zero mmap offset.

IMHO, this approach is way simpler, and easier to get it correct at
each call site, rather than the current approach which seems to be
error-prone.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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Re: [PATCH v5 0/9] Use vm_insert_range

[Souptick Joarder]

On Mon, Dec 24, 2018 at 8:51 PM Russell King - ARM Linux
<linux@armlinux.org.uk> wrote:
>
> Having discussed with Matthew offlist, I think we've come to the
> following conclusion - there's a number of drivers that buggily
> ignore vm_pgoff.
>
> So, what I proposed is:
>
> static int __vm_insert_range(struct vm_struct *vma, struct page *pages,
>                              size_t num, unsigned long offset)
> {
>         unsigned long count = vma_pages(vma);
>         unsigned long uaddr = vma->vm_start;
>         int ret;
>
>         /* Fail if the user requested offset is beyond the end of the object */
>         if (offset > num)
>                 return -ENXIO;
>
>         /* Fail if the user requested size exceeds available object size */
>         if (count > num - offset)
>                 return -ENXIO;
>
>         /* Never exceed the number of pages that the user requested */
>         for (i = 0; i < count; i++) {
>                 ret = vm_insert_page(vma, uaddr, pages[offset + i]);
>                 if (ret < 0)
>                         return ret;
>                 uaddr += PAGE_SIZE;
>         }
>
>         return 0;
> }
>
> /*
>  * Maps an object consisting of `num' `pages', catering for the user's
>  * requested vm_pgoff
>  */
> int vm_insert_range(struct vm_struct *vma, struct page *pages, size_t num)
> {
>         return __vm_insert_range(vma, pages, num, vma->vm_pgoff);
> }
>
> /*
>  * Maps a set of pages, always starting at page[0]
>  */
> int vm_insert_range_buggy(struct vm_struct *vma, struct page *pages, size_t num)
> {
>         return __vm_insert_range(vma, pages, num, 0);
> }
>
> With this, drivers such as iommu/dma-iommu.c can be converted thusly:
>
>  int iommu_dma_mmap(struct page **pages, size_t size, struct vm_area_struct *vma+)
>  {
> -       unsigned long uaddr = vma->vm_start;
> -       unsigned int i, count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> -       int ret = -ENXIO;
> -
> -       for (i = vma->vm_pgoff; i < count && uaddr < vma->vm_end; i++) {
> -               ret = vm_insert_page(vma, uaddr, pages[i]);
> -               if (ret)
> -                       break;
> -               uaddr += PAGE_SIZE;
> -       }
> -       return ret;
> +       return vm_insert_range(vma, pages, PAGE_ALIGN(size) >> PAGE_SHIFT);
> }
>
> and drivers such as firewire/core-iso.c:
>
>  int fw_iso_buffer_map_vma(struct fw_iso_buffer *buffer,
>                           struct vm_area_struct *vma)
>  {
> -       unsigned long uaddr;
> -       int i, err;
> -
> -       uaddr = vma->vm_start;
> -       for (i = 0; i < buffer->page_count; i++) {
> -               err = vm_insert_page(vma, uaddr, buffer->pages[i]);
> -               if (err)
> -                       return err;
> -
> -               uaddr += PAGE_SIZE;
> -       }
> -
> -       return 0;
> +       return vm_insert_range_buggy(vma, buffer->pages, buffer->page_count);
> }
>
> and this gives us something to grep for to find these buggy drivers.
>
> Now, this may not look exactly equivalent, but if you look at
> fw_device_op_mmap(), buffer->page_count is basically vma_pages(vma)
> at this point, which means this should be equivalent.
>
> We _could_ then at a later date "fix" these drivers to behave according
> to the normal vm_pgoff offsetting simply by removing the _buggy suffix
> on the function name... and if that causes regressions, it gives us an
> easy way to revert (as long as vm_insert_range_buggy() remains
> available.)
>
> In the case of firewire/core-iso.c, it currently ignores the mmap offset
> entirely, so making the above suggested change would be tantamount to
> causing it to return -ENXIO for any non-zero mmap offset.
>
> IMHO, this approach is way simpler, and easier to get it correct at
> each call site, rather than the current approach which seems to be
> error-prone.

Thanks Russell.
I will drop this patch series and rework on it as suggested.