Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754906AbaDPToK (ORCPT ); Wed, 16 Apr 2014 15:44:10 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:45350 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754023AbaDPToI (ORCPT ); Wed, 16 Apr 2014 15:44:08 -0400 Date: Wed, 16 Apr 2014 12:44:06 -0700 From: Andrew Morton To: Akinobu Mita Cc: linux-kernel@vger.kernel.org, Marek Szyprowski , Konrad Rzeszutek Wilk , David Woodhouse , Don Dutile , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andi Kleen , x86@kernel.org, iommu@lists.linux-foundation.org Subject: Re: [PATCH v3 1/5] x86: make dma_alloc_coherent() return zeroed memory if CMA is enabled Message-Id: <20140416124406.b6a3f8c9f6e7eb7328ebb5cb@linux-foundation.org> In-Reply-To: <1397567329-3771-2-git-send-email-akinobu.mita@gmail.com> References: <1397567329-3771-1-git-send-email-akinobu.mita@gmail.com> <1397567329-3771-2-git-send-email-akinobu.mita@gmail.com> X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 15 Apr 2014 22:08:45 +0900 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() > > 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. > > Alternatively, we could fix dma_alloc_from_contiguous() to return > zeroed out memory and remove memset() from all caller of it. But we > can't simply remove the memset on arm because __dma_clear_buffer() is > used there for ensuring cache flushing and it is used in many places. > Of course we can do redundant memset in dma_alloc_from_contiguous(), > but I think this patch is less impact for fixing this problem. But this patch does a duplicated memset if the page was allocated by alloc_pages_node()? Would it not be better to pass the gfp_t to dma_alloc_from_contiguous() and have it implement __GFP_ZERO? That will fix thsi inefficiency, will be symmetrical with the other underlying allocators and should permit the appropriate fixups in arm? > --- 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; > /* CMA can be used only in the context which permits sleeping */ > @@ -120,7 +119,7 @@ again: > > return NULL; > } > - > + memset(page_address(page), 0, size); > *dma_addr = addr; > return page_address(page); > } > -- > 1.8.3.2 -- 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/