Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756707Ab3GWKhY (ORCPT ); Tue, 23 Jul 2013 06:37:24 -0400 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:38216 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756328Ab3GWKhX (ORCPT ); Tue, 23 Jul 2013 06:37:23 -0400 Date: Tue, 23 Jul 2013 11:37:04 +0100 From: Russell King - ARM Linux To: Rusty Russell Cc: monstr@monstr.eu, Jens Axboe , LKML , Ohad Ben-Cohen , linux-arm-kernel@lists.infradead.org Subject: Re: scatterlist: sg_set_buf() argument must be in linear mapping (sha1: ac4e97abce9b80c020e7113325f49e58b7b15e3f) Message-ID: <20130723103704.GS24642@n2100.arm.linux.org.uk> References: <51E64C6B.3080306@monstr.eu> <87siz7xt4z.fsf@rustcorp.com.au> <51ED2C74.7050502@monstr.eu> <87ppua9feh.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87ppua9feh.fsf@rustcorp.com.au> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2181 Lines: 52 On Tue, Jul 23, 2013 at 12:00:30PM +0930, Rusty Russell wrote: > Michal Simek writes: > > Let me take some code from virtio_rpmsg_bus.c to show that problematic part. > > > > bufs_va = dma_alloc_coherent(vdev->dev.parent->parent, > > RPMSG_TOTAL_BUF_SPACE, > > &vrp->bufs_dma, GFP_KERNEL); > > vrp->rbufs = bufs_va; > > for (i = 0; i < RPMSG_NUM_BUFS / 2; i++) { > > struct scatterlist sg; > > void *cpu_addr = vrp->rbufs + i * RPMSG_BUF_SIZE; > > > > sg_init_one(&sg, cpu_addr, RPMSG_BUF_SIZE); > > } > > Hmm. Looking at arch/arm/include/asm/memory.h: > > #define virt_to_page(kaddr) pfn_to_page(__pa(kaddr) >> PAGE_SHIFT) > #define virt_addr_valid(kaddr) ((unsigned long)(kaddr) >= PAGE_OFFSET && (unsigned long)(kaddr) < (unsigned long)high_memory) > > pfn_to_page in ARM seems to be the asm-generic one, which depends on > CONFIG_SPARSEMEM/CONFIG_DISCONTIGMEM/CONFIG_FLATMEM etc. > > Perhaps virt_addr_valid() is wrong for your config? It's pretty clear > that you shouldn't call virt_to_page() on something for which > !virt_addr_valid(). The above code fragment is just wrong. You can't make any assumptions about the memory returned from dma_alloc_coherent(), because: - On x86, it is kernel direct mapped memory, where things like virt_to_phys(cpuaddr) will work fine with it. - On any architecture which needs to remap memory to make it coherent with the DMA device, the key word there is "remap" - it's not kernel direct mapped memory, and virt_to_phys(cpuaddr) on it is illegal. The only valid operation with scatterlists and such memory returned from dma_alloc_coherent() is: sg_dma_address(sg) = dma_address; sg_dma_len(sg) = dma_length; and not to use the virtual address(es) at all in the scatterlist. And it is very very important to realise that you must not mix the streaming and coherent DMA APIs - you must never pass coherent memory into the dma_map_* functions. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/