linux-stable/samples/vfio-mdev
Marek Szyprowski be0704beb2 samples: vfio-mdev/mbochs: fix common struct sg_table related issues
The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg() function
returns the number of the created entries in the DMA address space.
However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
dma_unmap_sg must be called with the original number of the entries
passed to the dma_map_sg().

struct sg_table is a common structure used for describing a non-contiguous
memory buffer, used commonly in the DRM and graphics subsystems. It
consists of a scatterlist with memory pages and DMA addresses (sgl entry),
as well as the number of scatterlist entries: CPU pages (orig_nents entry)
and DMA mapped pages (nents entry).

It turned out that it was a common mistake to misuse nents and orig_nents
entries, calling DMA-mapping functions with a wrong number of entries or
ignoring the number of mapped entries returned by the dma_map_sg()
function.

To avoid such issues, lets use a common dma-mapping wrappers operating
directly on the struct sg_table objects and use scatterlist page
iterators where possible. This, almost always, hides references to the
nents and orig_nents entries, making the code robust, easier to follow
and copy/paste safe.

While touching this code, also add missing call to dma_unmap_sgtable.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
2020-09-10 08:19:46 +02:00
..
Makefile treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
mbochs.c samples: vfio-mdev/mbochs: fix common struct sg_table related issues 2020-09-10 08:19:46 +02:00
mdpy-defs.h PCI: Move PCI_VENDOR_ID_REDHAT definition to pci_ids.h 2020-07-09 17:00:47 -05:00
mdpy-fb.c samples: vfio-mdev: constify fb ops 2019-12-10 08:52:15 +02:00
mdpy.c vmalloc: fix remap_vmalloc_range() bounds checks 2020-04-21 11:11:56 -07:00
mtty.c vfio-mdev/mtty: Simplify interrupt generation 2019-08-19 13:28:57 -06:00