From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754605Ab0CDE6R (ORCPT ); Wed, 3 Mar 2010 23:58:17 -0500 Received: from sh.osrg.net ([192.16.179.4]:33493 "EHLO sh.osrg.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751954Ab0CDE6O (ORCPT ); Wed, 3 Mar 2010 23:58:14 -0500 Date: Thu, 4 Mar 2010 13:58:06 +0900 To: hancockrwd@gmail.com Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, linux-usb@vger.kernel.org, davem@davemloft.net, bzolnier@gmail.com Subject: Re: [PATCH RFC] fix problems with NETIF_F_HIGHDMA in networking drivers v2 From: FUJITA Tomonori In-Reply-To: <4B8F213B.40603@gmail.com> References: <4B8F213B.40603@gmail.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-Id: <20100304135738C.fujita.tomonori@lab.ntt.co.jp> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-3.0 (sh.osrg.net [192.16.179.4]); Thu, 04 Mar 2010 13:58:07 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 03 Mar 2010 20:55:55 -0600 Robert Hancock wrote: > Many networking drivers have issues with the use of the NETIF_F_HIGHDMA flag. > This flag actually indicates whether or not the device/driver can handle > skbs located in high memory (as opposed to lowmem). If the flag isn't set and > the skb is located in highmem, it needs to be copied. > There are two problems with this flag: > > -Many drivers only set the flag when they detect they can use 64-bit DMA, > since otherwise they could receive DMA addresses that they can't handle > (which on platforms without IOMMU/SWIOTLB support is fatal). This means that if > 64-bit support isn't available, even buffers located below 4GB will get copied > unnecessarily. > > -Some drivers set the flag even though they can't actually handle 64-bit DMA, > which would mean that on platforms without IOMMU/SWIOTLB they would get a DMA > mapping error if the memory they received happened to be located above 4GB. > > In order to fix this problem, the existing NETIF_F_HIGHDMA flag is split into > two new flags: > > NETIF_F_DMA_HIGH - indicates if the driver can do DMA to highmem at all > NETIF_F_DMA_64BIT - indicates the driver can do DMA to 64-bit memory Why can't you use dev->dma_mask here like the following? Then you can fix drivers that use the NETIF_F_HIGHDMA flag to indicate that they don't support 64bit DMA. diff --git a/net/core/dev.c b/net/core/dev.c index bcc490c..b15f94b 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -129,6 +129,7 @@ #include #include #include +#include #include "net-sysfs.h" @@ -1787,14 +1788,21 @@ static inline int illegal_highdma(struct net_device *dev, struct sk_buff *skb) { #ifdef CONFIG_HIGHMEM int i; + if (!(dev->features & NETIF_F_HIGHDMA)) { + for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) + if (PageHighMem(skb_shinfo(skb)->frags[i].page)) + return 1; + } - if (dev->features & NETIF_F_HIGHDMA) - return 0; - - for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) - if (PageHighMem(skb_shinfo(skb)->frags[i].page)) - return 1; + if (PCI_DMA_BUS_IS_PHYS) { + struct device *pdev = dev->dev.parent; + for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) { + dma_addr_t addr = page_to_phys(skb_shinfo(skb)->frags[i].page); + if (!pdev->dma_mask || addr + PAGE_SIZE - 1 > *pdev->dma_mask) + return 1; + } + } #endif return 0; }