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dma-debug: check scatterlist segments

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Drivers/subsystems creating scatterlists for DMA should be taking care
to respect the scatter-gather limitations of the appropriate device, as
described by dma_parms. A DMA API implementation cannot feasibly split
a scatterlist into *more* entries than originally passed, so it is not
well defined what they should do when given a segment larger than the
limit they are also required to respect.

Conversely, devices which are less limited than the rather conservative
defaults, or indeed have no limitations at all (e.g. GPUs with their own
internal MMU), should be encouraged to set appropriate dma_parms, as
they may get more efficient DMA mapping performance out of it.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
This commit is contained in:
Robin Murphy 2018-05-21 12:35:13 +01:00 committed by Christoph Hellwig
parent 7f5c1ea3b7
commit 78c47830a5
2 changed files with 45 additions and 0 deletions
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17
lib/Kconfig.debug
View File

@ -1651,6 +1651,23 @@ config DMA_API_DEBUG
If unsure, say N.
config DMA_API_DEBUG_SG
bool "Debug DMA scatter-gather usage"
default y
depends on DMA_API_DEBUG
help
Perform extra checking that callers of dma_map_sg() have respected the
appropriate segment length/boundary limits for the given device when
preparing DMA scatterlists.
This is particularly likely to have been overlooked in cases where the
dma_map_sg() API is used for general bulk mapping of pages rather than
preparing literal scatter-gather descriptors, where there is a risk of
unexpected behaviour from DMA API implementations if the scatterlist
is technically out-of-spec.
If unsure, say N.
menuconfig RUNTIME_TESTING_MENU
bool "Runtime Testing"
def_bool y

28
lib/dma-debug.c
View File

@ -1286,6 +1286,32 @@ out:
put_hash_bucket(bucket, &flags);
}
static void check_sg_segment(struct device *dev, struct scatterlist *sg)
{
#ifdef CONFIG_DMA_API_DEBUG_SG
unsigned int max_seg = dma_get_max_seg_size(dev);
u64 start, end, boundary = dma_get_seg_boundary(dev);
/*
* Either the driver forgot to set dma_parms appropriately, or
* whoever generated the list forgot to check them.
*/
if (sg->length > max_seg)
err_printk(dev, NULL, "DMA-API: mapping sg segment longer than device claims to support [len=%u] [max=%u]\n",
sg->length, max_seg);
/*
* In some cases this could potentially be the DMA API
* implementation's fault, but it would usually imply that
* the scatterlist was built inappropriately to begin with.
*/
start = sg_dma_address(sg);
end = start + sg_dma_len(sg) - 1;
if ((start ^ end) & ~boundary)
err_printk(dev, NULL, "DMA-API: mapping sg segment across boundary [start=0x%016llx] [end=0x%016llx] [boundary=0x%016llx]\n",
start, end, boundary);
#endif
}
void debug_dma_map_page(struct device *dev, struct page *page, size_t offset,
size_t size, int direction, dma_addr_t dma_addr,
bool map_single)
@ -1416,6 +1442,8 @@ void debug_dma_map_sg(struct device *dev, struct scatterlist *sg,
check_for_illegal_area(dev, sg_virt(s), sg_dma_len(s));
}
check_sg_segment(dev, s);
add_dma_entry(entry);
}
}