| Message ID | 20181224131841.GA22017@jordon-HP-15-Notebook-PC (mailing list archive) |
|---|---|
| Headers | show |
| Series | Use vm_insert_range | expand |
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.
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.
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(-)