diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h index 31f114f486c4..9bf19b5bf755 100644 --- a/include/linux/dma-map-ops.h +++ b/include/linux/dma-map-ops.h @@ -8,6 +8,7 @@ #include #include +#include struct cma; @@ -277,6 +278,66 @@ static inline bool dev_is_dma_coherent(struct device *dev) } #endif /* CONFIG_ARCH_HAS_DMA_COHERENCE_H */ +/* + * Check whether potential kmalloc() buffers are safe for non-coherent DMA. + */ +static inline bool dma_kmalloc_safe(struct device *dev, + enum dma_data_direction dir) +{ + /* + * If DMA bouncing of kmalloc() buffers is disabled, the kmalloc() + * caches have already been aligned to a DMA-safe size. + */ + if (!IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC)) + return true; + + /* + * kmalloc() buffers are DMA-safe irrespective of size if the device + * is coherent or the direction is DMA_TO_DEVICE (non-desctructive + * cache maintenance and benign cache line evictions). + */ + if (dev_is_dma_coherent(dev) || dir == DMA_TO_DEVICE) + return true; + + return false; +} + +/* + * Check whether the given size, assuming it is for a kmalloc()'ed buffer, is + * sufficiently aligned for non-coherent DMA. + */ +static inline bool dma_kmalloc_size_aligned(size_t size) +{ + /* + * Larger kmalloc() sizes are guaranteed to be aligned to + * ARCH_DMA_MINALIGN. + */ + if (size >= 2 * ARCH_DMA_MINALIGN || + IS_ALIGNED(kmalloc_size_roundup(size), dma_get_cache_alignment())) + return true; + + return false; +} + +/* + * Check whether the given object size may have originated from a kmalloc() + * buffer with a slab alignment below the DMA-safe alignment and needs + * bouncing for non-coherent DMA. The pointer alignment is not considered and + * in-structure DMA-safe offsets are the responsibility of the caller. Such + * code should use the static ARCH_DMA_MINALIGN for compiler annotations. + * + * The heuristics can have false positives, bouncing unnecessarily, though the + * buffers would be small. False negatives are theoretically possible if, for + * example, multiple small kmalloc() buffers are coalesced into a larger + * buffer that passes the alignment check. There are no such known constructs + * in the kernel. + */ +static inline bool dma_kmalloc_needs_bounce(struct device *dev, size_t size, + enum dma_data_direction dir) +{ + return !dma_kmalloc_safe(dev, dir) && !dma_kmalloc_size_aligned(size); +} + void *arch_dma_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs); void arch_dma_free(struct device *dev, size_t size, void *cpu_addr, diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig index acc6f231259c..abea1823fe21 100644 --- a/kernel/dma/Kconfig +++ b/kernel/dma/Kconfig @@ -90,6 +90,10 @@ config SWIOTLB bool select NEED_DMA_MAP_STATE +config DMA_BOUNCE_UNALIGNED_KMALLOC + bool + depends on SWIOTLB + config DMA_RESTRICTED_POOL bool "DMA Restricted Pool" depends on OF && OF_RESERVED_MEM && SWIOTLB diff --git a/kernel/dma/direct.h b/kernel/dma/direct.h index e38ffc5e6bdd..97ec892ea0b5 100644 --- a/kernel/dma/direct.h +++ b/kernel/dma/direct.h @@ -94,7 +94,8 @@ static inline dma_addr_t dma_direct_map_page(struct device *dev, return swiotlb_map(dev, phys, size, dir, attrs); } - if (unlikely(!dma_capable(dev, dma_addr, size, true))) { + if (unlikely(!dma_capable(dev, dma_addr, size, true)) || + dma_kmalloc_needs_bounce(dev, size, dir)) { if (is_pci_p2pdma_page(page)) return DMA_MAPPING_ERROR; if (is_swiotlb_active(dev))