From 78c47830a5cbb5d22dc91819a95af3d5c4bec084 Mon Sep 17 00:00:00 2001 From: Robin Murphy Date: Mon, 21 May 2018 12:35:13 +0100 Subject: [PATCH] dma-debug: check scatterlist segments 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 Signed-off-by: Christoph Hellwig --- lib/Kconfig.debug | 17 +++++++++++++++++ lib/dma-debug.c | 28 ++++++++++++++++++++++++++++ 2 files changed, 45 insertions(+) diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index d5175eb..7655547 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -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 diff --git a/lib/dma-debug.c b/lib/dma-debug.c index 6a1ebaa..c007d25 100644 --- a/lib/dma-debug.c +++ b/lib/dma-debug.c @@ -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); } } -- 2.7.4