* ?????? ??????? | 2009-10-20 18:28:34 [+0400]: >Dear all, I have a couple of questions about crypto internals, please >help me to understand some concepts. My drivers implements >CRYPTO_ALG_TYPE_BLKCIPHER algorithm and has to perform encryption via >DMA transfers. In the end you might prefer to use CRYPTO_ALG_TYPE_ABLKCIPHER. The difference is that you could enqueue multiple transfers on the HW and receive an interrupt once it is done. >I decided to use blkcipher_walk_phys() and blkcipher_walk_done() >functions. These functions take scatterlist and return one or more >struct page's and offsets. Then i pass those to dma_map_page() which >returns dma_addr_t to send to my device's DMA engine. >Everything seems to work (on ARM) but i have several questions: > >1. Is it generally correct to do this? (see *_encrypt() handler below) See comment below >2. Article at http://linux-mm.org/DeviceDriverMmap >says "You may be tempted to call virt_to_page(addr) to get a struct >page pointer for a kmalloced address, but this is a violation of the >abstraction: kmalloc does not return pages, it returns another type of >memory object." >And blkcipher_walk_init() internally calls virt_to_page() on a pointer It does not: |static inline void blkcipher_walk_init(struct blkcipher_walk *walk, | struct scatterlist *dst, | struct scatterlist *src, | unsigned int nbytes) |{ | walk->in.sg = src; | walk->out.sg = dst; | walk->total = nbytes; |} >allocated from unknown location (for example, in tcrypt.c there is >statically allocated buffer, but it is just one case of many). Is it >correct and how to think about it? virt_to_page() is safe as long as you don't have HIGHMEM support or you receive memory from vmalloc(). The blkcipher uses scatterwalk_map() for src/dst which in turn ends up in kmap() what ensures that virt_to_page() works on that page. In case it was a HIGHMEM page, it will be copied into kernel address range and on unmap it will be copied back. And here is some overhead: your HW should be able to access the HIGHMEM page directly. >static int mcrypto_3des_ecb_encrypt(struct blkcipher_desc *desc, > struct scatterlist *dst, struct scatterlist *src, unsigned int nbytes) >{ > struct mcrypto_device *device = &g_mcrypto_device; > struct mcrypto_3des_ctx *ctx = crypto_blkcipher_ctx(desc->tfm); > struct blkcipher_walk walk; > int err; > > blkcipher_walk_init(&walk, dst, src, nbytes); > err = blkcipher_walk_phys(desc, &walk); > ctx->mode = mcrypto_encrypt; > > while((nbytes = walk.nbytes)) { > dma_addr_t src_dma, dst_dma; > size_t size = nbytes - (nbytes % DES3_EDE_MIN_BLOCK_SIZE); > > src_dma = dma_map_page(device->dev, walk.src.phys.page, > walk.src.phys.offset, size, DMA_TO_DEVICE); > dst_dma = dma_map_page(device->dev, walk.dst.phys.page, > walk.dst.phys.offset, size, DMA_FROM_DEVICE); It might happen that walk.src.phys.page == walk.dst.phys.page. In that case you should use DMA_BIDIRECTIONAL > > /* Performs actual DMA transfers and waits for completion */ > mcrypto_3des_dmacrypt(device, ctx, src_dma, dst_dma, size); > > dma_unmap_page(device->dev, dst_dma, size, DMA_FROM_DEVICE); > dma_unmap_page(device->dev, src_dma, size, DMA_TO_DEVICE); > > err = blkcipher_walk_done(desc, &walk, nbytes-size); > } > return err; >} Sebastian -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
