Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752685AbdF0LSY (ORCPT ); Tue, 27 Jun 2017 07:18:24 -0400 Received: from mail-yb0-f176.google.com ([209.85.213.176]:35272 "EHLO mail-yb0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751632AbdF0LSS (ORCPT ); Tue, 27 Jun 2017 07:18:18 -0400 MIME-Version: 1.0 In-Reply-To: References: <20170627072812.15316-1-tfiga@chromium.org> From: Tomasz Figa Date: Tue, 27 Jun 2017 20:17:55 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 1/2] iommu/dma: Respect __GFP_DMA and __GFP_DMA32 in incoming GFP flags To: Robin Murphy Cc: "open list:IOMMU DRIVERS" , "linux-kernel@vger.kernel.org" , Joerg Roedel Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2253 Lines: 58 On Tue, Jun 27, 2017 at 8:01 PM, Robin Murphy wrote: > On 27/06/17 08:28, Tomasz Figa wrote: >> Current implementation of __iommu_dma_alloc_pages() keeps adding >> __GFP_HIGHMEM to GFP flags regardless of whether other zone flags are >> already included in the incoming flags. If __GFP_DMA or __GFP_DMA32 is >> set at the same time as __GFP_HIGHMEM, the allocation fails due to >> invalid zone flag combination. >> >> Fix this by checking for __GFP_DMA and __GFP_DMA32 in incoming GFP flags >> and adding __GFP_HIGHMEM only if they are not present. > > Wouldn't it make more sense to strip off the ZONE_DMA* related flags, > since the whole point here is that we don't care where the pages come from? I guess for my use case it wouldn't break things, as I strip them in my DMA mapping implementation right now (+/- one minor detail below). However I recall existing IOMMUs that could only use pages from within the 32-bit address space (e.g. Tegra X1). Also the IOMMU I'm working on is a part of a PCI device and it might actually prefer 32-bit addressable memory as well (to avoid DAC addressing; I still need to evaluate this). With this said, maybe it could actually make sense to leave the choice to the DMA mapping implementation? Best regards, Tomasz > > Robin. > >> Signed-off-by: Tomasz Figa >> --- >> drivers/iommu/dma-iommu.c | 10 ++++++++-- >> 1 file changed, 8 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c >> index 9d1cebe7f6cb..29965a092a69 100644 >> --- a/drivers/iommu/dma-iommu.c >> +++ b/drivers/iommu/dma-iommu.c >> @@ -445,8 +445,14 @@ static struct page **__iommu_dma_alloc_pages(unsigned int count, >> if (!pages) >> return NULL; >> >> - /* IOMMU can map any pages, so himem can also be used here */ >> - gfp |= __GFP_NOWARN | __GFP_HIGHMEM; >> + /* >> + * IOMMU can map any pages, so himem can also be used here, >> + * unless another DMA zone is explicitly requested. >> + */ >> + if (!(gfp & (__GFP_DMA | __GFP_DMA32))) >> + gfp |= __GFP_HIGHMEM; >> + >> + gfp |= __GFP_NOWARN; >> >> while (count) { >> struct page *page = NULL; >> >