From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966548Ab0B0MAl (ORCPT ); Sat, 27 Feb 2010 07:00:41 -0500 Received: from mail-fx0-f219.google.com ([209.85.220.219]:46121 "EHLO mail-fx0-f219.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966055Ab0B0MAj (ORCPT ); Sat, 27 Feb 2010 07:00:39 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=from:to:subject:date:user-agent:cc:references:in-reply-to :mime-version:message-id:content-type:content-transfer-encoding; b=CUf7TsmkEYAFOXMh1JdQW3EdwotESUKeYf4UeZUWCg/m+fMq4NP6wRFwpN/luyeRWT yPLOpzZCM8YorW7tPaGCyOL1VYGFCX4qfi0FnoqJvUmPncibwNwJ1hK46BXvimROtQpm ua3OAHsvqcuXok9vJ8SQ6meuUZqS0Xit6l7uA= From: Bartlomiej Zolnierkiewicz To: David Miller Subject: Re: [RFC PATCH] fix problems with NETIF_F_HIGHDMA in networking drivers Date: Sat, 27 Feb 2010 12:59:31 +0100 User-Agent: KMail/1.12.4 (Linux/2.6.31.12-0.1-desktop; KDE/4.3.5; x86_64; ; ) Cc: hancockrwd@gmail.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, linux-usb@vger.kernel.org References: <51f3faa71002260646r705891e8tdbab1f6faeeb4b81@mail.gmail.com> <51f3faa71002261908y7cfa62eeicb3e56d5c920887a@mail.gmail.com> <20100227.015350.71138134.davem@davemloft.net> In-Reply-To: <20100227.015350.71138134.davem@davemloft.net> MIME-Version: 1.0 Message-Id: <201002271259.31596.bzolnier@gmail.com> Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Saturday 27 February 2010 10:53:50 am David Miller wrote: > From: Robert Hancock > Date: Fri, 26 Feb 2010 21:08:04 -0600 > > > That seems like a reasonable approach to me. Only question is how to > > implement the check for DMA_64BIT. Can we just check page_to_phys on > > each of the pages in the skb to see if it's > 0xffffffff ? Are there > > any architectures where it's more complicated than that? > > On almost every platform it's "more complicated than that". Mildly speaking, I see the real problem now and it is much higher in the software stack than networking.. > This is the whole issue. What matters is the final DMA address and > since we have IOMMUs and the like, it is absolutely not tenable to > solve this by checking physical address attributes. What's more we may not have IOMMU in place which creates really interesting scenarios for HIGHMEM=y and results in all kind of wonderful band-aids in particular device drivers. Having IOMMU (even if it is only a software one, i.e. this would mean swiotlb for x86-32/highmem) always in place would simplify things greatly.. -- Bartlomiej Zolnierkiewicz