Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753818AbaA0PY6 (ORCPT ); Mon, 27 Jan 2014 10:24:58 -0500 Received: from aserp1040.oracle.com ([141.146.126.69]:17351 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753500AbaA0PY5 (ORCPT ); Mon, 27 Jan 2014 10:24:57 -0500 Date: Mon, 27 Jan 2014 10:23:42 -0500 From: Konrad Rzeszutek Wilk To: Marek Szyprowski Cc: Akinobu Mita , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, David Woodhouse , Don Dutile , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andi Kleen , x86@kernel.org, iommu@lists.linux-foundation.org Subject: Re: [PATCH v2 1/5] x86: make dma_alloc_coherent() return zeroed memory if CMA is enabled Message-ID: <20140127152342.GC20968@phenom.dumpdata.com> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <52E66527.8010000@samsung.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Source-IP: acsinet22.oracle.com [141.146.126.238] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > > >Most implementations of dma_alloc_coherent() return zeroed memory > >regardless of whether __GFP_ZERO is specified. So this fixes it by > >unconditionally zeroing the allocated memory region. > > > >Cc: Marek Szyprowski > >Cc: Konrad Rzeszutek Wilk > >Cc: David Woodhouse > >Cc: Don Dutile > >Cc: Thomas Gleixner > >Cc: Ingo Molnar > >Cc: "H. Peter Anvin" > >Cc: Andi Kleen > >Cc: x86@kernel.org > >Cc: iommu@lists.linux-foundation.org > >Signed-off-by: Akinobu Mita > >--- > >New patch from this version > > > > arch/x86/kernel/pci-dma.c | 3 +-- > > 1 file changed, 1 insertion(+), 2 deletions(-) > > > >diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c > >index 872079a..9644405 100644 > >--- a/arch/x86/kernel/pci-dma.c > >+++ b/arch/x86/kernel/pci-dma.c > >@@ -97,7 +97,6 @@ void *dma_generic_alloc_coherent(struct device *dev, size_t size, > > dma_mask = dma_alloc_coherent_mask(dev, flag); > >- flag |= __GFP_ZERO; > > again: > > page = NULL; > > if (!(flag & GFP_ATOMIC)) > >@@ -118,7 +117,7 @@ again: > > return NULL; > > } > >- > >+ memset(page_address(page), 0, size); > > *dma_addr = addr; > > return page_address(page); > > } > > Best regards > -- > Marek Szyprowski, PhD > Samsung R&D Institute Poland > -- 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/