Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752765AbaBCMOn (ORCPT ); Mon, 3 Feb 2014 07:14:43 -0500 Received: from mail-oa0-f53.google.com ([209.85.219.53]:43497 "EHLO mail-oa0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752487AbaBCMOi (ORCPT ); Mon, 3 Feb 2014 07:14:38 -0500 MIME-Version: 1.0 In-Reply-To: References: <1389708830-5841-1-git-send-email-akinobu.mita@gmail.com> <1389708830-5841-2-git-send-email-akinobu.mita@gmail.com> <52E66527.8010000@samsung.com> <20140127152342.GC20968@phenom.dumpdata.com> Date: Mon, 3 Feb 2014 21:14:37 +0900 Message-ID: Subject: Re: [PATCH v2 1/5] x86: make dma_alloc_coherent() return zeroed memory if CMA is enabled From: Akinobu Mita To: Konrad Rzeszutek Wilk Cc: Marek Szyprowski , LKML , Andrew Morton , David Woodhouse , Don Dutile , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andi Kleen , x86@kernel.org, iommu@lists.linux-foundation.org Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2014-01-29 Akinobu Mita : > 2014-01-28 Konrad Rzeszutek Wilk : >> On Mon, Jan 27, 2014 at 02:54:47PM +0100, Marek Szyprowski wrote: >>> Hello, >>> >>> On 2014-01-14 15:13, Akinobu Mita wrote: >>> >Calling dma_alloc_coherent() with __GFP_ZERO must return zeroed memory. >>> > >>> >But when the contiguous memory allocator (CMA) is enabled on x86 and >>> >the memory region is allocated by dma_alloc_from_contiguous(), it >>> >doesn't return zeroed memory. Because dma_generic_alloc_coherent() >>> >forgot to fill the memory region with zero if it was allocated by >>> >dma_alloc_from_contiguous() >>> >>> I just wonder how it will work with high mem? I've didn't check the x86 >>> dma mapping code yet, but page_address() works only for pages, which comes >>> from low memory. In other patches you have added an option to place CMA >>> area anywhere in the memory. Is the x86 pci dma code ready for the case >>> when cma area is put into high mem and direct mappings are not available? >> >> Yes and no. The swiotbl_bounce does have the code to take that into account. >> But that is it - nothing else does - so I think you would run in the >> possiblity of 'page_address' not providing an correct virtual address. > > Thanks for spotting the issue. I haven't much tested on x86_32. > I'll go through it and try to find the solution. I have confirmed that locating CMA on highmem range with a 'cma=size@start-end' kernel parameter by this patch set caused the issue on x86_32. This can be fixed by limiting CMA area upto max_low_pfn to prevent from locating it on highmem at arch/x86/kernel/setup.c:setup_arch() - dma_contiguous_reserve(0); + dma_contiguous_reserve(max_low_pfn << PAGE_SHIFT); I'm going to inlcude this change in this patch set. -- 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/