From: Leon Romanovsky <[email protected]> Rename the DMA_ATTR_CPU_CACHE_CLEAN attribute to reflect that it allows CPU cache overlaps to exist, and document a slightly different but still valid use case involving overlapping CPU cache lines.
Signed-off-by: Leon Romanovsky <[email protected]> --- Documentation/core-api/dma-attributes.rst | 26 ++++++++++++++++++-------- drivers/virtio/virtio_ring.c | 4 ++-- include/linux/dma-mapping.h | 8 ++++---- kernel/dma/debug.c | 2 +- 4 files changed, 25 insertions(+), 15 deletions(-) diff --git a/Documentation/core-api/dma-attributes.rst b/Documentation/core-api/dma-attributes.rst index 1d7bfad73b1c7..6b73d92c62721 100644 --- a/Documentation/core-api/dma-attributes.rst +++ b/Documentation/core-api/dma-attributes.rst @@ -149,11 +149,21 @@ For architectures that require cache flushing for DMA coherence DMA_ATTR_MMIO will not perform any cache flushing. The address provided must never be mapped cacheable into the CPU. -DMA_ATTR_CPU_CACHE_CLEAN ------------------------- - -This attribute indicates the CPU will not dirty any cacheline overlapping this -DMA_FROM_DEVICE/DMA_BIDIRECTIONAL buffer while it is mapped. This allows -multiple small buffers to safely share a cacheline without risk of data -corruption, suppressing DMA debug warnings about overlapping mappings. -All mappings sharing a cacheline should have this attribute. +DMA_ATTR_CPU_CACHE_OVERLAP +-------------------------- + +This attribute indicates that CPU cache lines may overlap for buffers mapped +with DMA_FROM_DEVICE or DMA_BIDIRECTIONAL. + +Such overlap may occur when callers map multiple small buffers that reside +within the same cache line. In this case, callers must guarantee that the CPU +will not dirty these cache lines after the mappings are established. When this +condition is met, multiple buffers can safely share a cache line without risking +data corruption. + +Another valid use case is on systems that are CPU-coherent and do not use +SWIOTLB, where the caller can guarantee that no cache maintenance operations +(such as flushes) will be performed that could overwrite shared cache lines. + +All mappings that share a cache line must set this attribute to suppress DMA +debug warnings about overlapping mappings. diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 335692d41617a..bf51ae9a39169 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -2912,7 +2912,7 @@ EXPORT_SYMBOL_GPL(virtqueue_add_inbuf); * @data: the token identifying the buffer. * @gfp: how to do memory allocations (if necessary). * - * Same as virtqueue_add_inbuf but passes DMA_ATTR_CPU_CACHE_CLEAN to indicate + * Same as virtqueue_add_inbuf but passes DMA_ATTR_CPU_CACHE_OVERLAP to indicate * that the CPU will not dirty any cacheline overlapping this buffer while it * is available, and to suppress overlapping cacheline warnings in DMA debug * builds. @@ -2928,7 +2928,7 @@ int virtqueue_add_inbuf_cache_clean(struct virtqueue *vq, gfp_t gfp) { return virtqueue_add(vq, &sg, num, 0, 1, data, NULL, false, gfp, - DMA_ATTR_CPU_CACHE_CLEAN); + DMA_ATTR_CPU_CACHE_OVERLAP); } EXPORT_SYMBOL_GPL(virtqueue_add_inbuf_cache_clean); diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h index 29973baa05816..45efede1a6cce 100644 --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -80,11 +80,11 @@ #define DMA_ATTR_MMIO (1UL << 10) /* - * DMA_ATTR_CPU_CACHE_CLEAN: Indicates the CPU will not dirty any cacheline - * overlapping this buffer while it is mapped for DMA. All mappings sharing - * a cacheline must have this attribute for this to be considered safe. + * DMA_ATTR_CPU_CACHE_OVERLAP: Indicates the CPU cache line can be overlapped. + * All mappings sharing a cacheline must have this attribute for this + * to be considered safe. */ -#define DMA_ATTR_CPU_CACHE_CLEAN (1UL << 11) +#define DMA_ATTR_CPU_CACHE_OVERLAP (1UL << 11) /* * A dma_addr_t can hold any valid DMA or bus address for the platform. It can diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c index be207be749968..603be342063f1 100644 --- a/kernel/dma/debug.c +++ b/kernel/dma/debug.c @@ -601,7 +601,7 @@ static void add_dma_entry(struct dma_debug_entry *entry, unsigned long attrs) unsigned long flags; int rc; - entry->is_cache_clean = !!(attrs & DMA_ATTR_CPU_CACHE_CLEAN); + entry->is_cache_clean = attrs & DMA_ATTR_CPU_CACHE_OVERLAP; bucket = get_hash_bucket(entry, &flags); hash_bucket_add(bucket, entry); -- 2.53.0
