lib: scatterlist: fix sg_split_phys to preserve original scatterlist offsets

The split_sg_phys function was incorrectly setting the offsets of all
scatterlist entries (except the first) to 0. Only

lib: scatterlist: fix sg_split_phys to preserve original scatterlist offsets

The split_sg_phys function was incorrectly setting the offsets of all
scatterlist entries (except the first) to 0. Only the first scatterlist
entry's offset and length needs to be modified to account for the skip.
Setting the rest entries' offsets to 0 could lead to incorrect data
access.

I am using this function in a crypto driver that I'm currently developing
(not yet sent to mailing list). During testing, it was observed that the
output scatterlists (except the first one) contained incorrect garbage
data.

I narrowed this issue down to the call of sg_split(). Upon debugging
inside this function, I found that this resetting of offset is the cause
of the problem, causing the subsequent scatterlists to point to incorrect
memory locations in a page. By removing this code, I am obtaining
expected data in all the split output scatterlists. Thus, this was indeed
causing observable runtime effects!

This patch removes the offending code, ensuring that the page offsets in
the input scatterlist are preserved in the output scatterlist.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: f8bcbe62acd0 ("lib: scatterlist: add sg splitting function")
Signed-off-by: T Pratham <[email protected]>
Cc: Robert Jarzmik <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Kamlesh Gurudasani <[email protected]>
Cc: Praneeth Bajjuri <[email protected]>
Cc: Vignesh Raghavendra <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

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lib: scatterlist: Fix to support no mapped sg

In function sg_split, the second sg_calculate_split will return -EINVAL
when in_mapped_nents is 0.

Indeed there is no need to do second sg_calculate_sp

lib: scatterlist: Fix to support no mapped sg

In function sg_split, the second sg_calculate_split will return -EINVAL
when in_mapped_nents is 0.

Indeed there is no need to do second sg_calculate_split and sg_split_mapped
when in_mapped_nents is 0, as in_mapped_nents indicates no mapped entry in
original sgl.

Signed-off-by: Zhou Wang <[email protected]>
Acked-by: Robert Jarzmik <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

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treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 230

Based on 2 normalized pattern(s):

this source code is licensed under the gnu general public license
version 2 see the file cop

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 230

Based on 2 normalized pattern(s):

this source code is licensed under the gnu general public license
version 2 see the file copying for more details

this source code is licensed under general public license version 2
see

extracted by the scancode license scanner the SPDX license identifier

GPL-2.0-only

has been chosen to replace the boilerplate/reference in 52 file(s).

Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Enrico Weigelt <[email protected]>
Reviewed-by: Allison Randal <[email protected]>
Reviewed-by: Alexios Zavras <[email protected]>
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

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lib: scatterlist: add sg splitting function

Sometimes a scatter-gather has to be split into several chunks, or sub
scatter lists. This happens for example if a scatter list will be
handled by multip

lib: scatterlist: add sg splitting function

Sometimes a scatter-gather has to be split into several chunks, or sub
scatter lists. This happens for example if a scatter list will be
handled by multiple DMA channels, each one filling a part of it.

A concrete example comes with the media V4L2 API, where the scatter list
is allocated from userspace to hold an image, regardless of the
knowledge of how many DMAs will fill it :
- in a simple RGB565 case, one DMA will pump data from the camera ISP
to memory
- in the trickier YUV422 case, 3 DMAs will pump data from the camera
ISP pipes, one for pipe Y, one for pipe U and one for pipe V

For these cases, it is necessary to split the original scatter list into
multiple scatter lists, which is the purpose of this patch.

The guarantees that are required for this patch are :
- the intersection of spans of any couple of resulting scatter lists is
empty.
- the union of spans of all resulting scatter lists is a subrange of
the span of the original scatter list.
- streaming DMA API operations (mapping, unmapping) should not happen
both on both the resulting and the original scatter list. It's either
the first or the later ones.
- the caller is reponsible to call kfree() on the resulting
scatterlists.

Signed-off-by: Robert Jarzmik <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

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