From owner-svn-src-all@FreeBSD.ORG Sat Jan 24 18:33:10 2015 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id BD4E3BAE; Sat, 24 Jan 2015 18:33:10 +0000 (UTC) Received: from pp2.rice.edu (proofpoint2.mail.rice.edu [128.42.201.101]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 7CE9FF81; Sat, 24 Jan 2015 18:33:09 +0000 (UTC) Received: from pps.filterd (pp2.rice.edu [127.0.0.1]) by pp2.rice.edu (8.14.5/8.14.5) with SMTP id t0OIWd7L021376; Sat, 24 Jan 2015 12:33:08 -0600 Received: from mh11.mail.rice.edu (mh11.mail.rice.edu [128.42.199.30]) by pp2.rice.edu with ESMTP id 1s3b7hrvft-1; Sat, 24 Jan 2015 12:33:08 -0600 X-Virus-Scanned: by amavis-2.7.0 at mh11.mail.rice.edu, auth channel Received: from 108-254-203-201.lightspeed.hstntx.sbcglobal.net (108-254-203-201.lightspeed.hstntx.sbcglobal.net [108.254.203.201]) (using TLSv1 with cipher RC4-MD5 (128/128 bits)) (No client certificate requested) (Authenticated sender: alc) by mh11.mail.rice.edu (Postfix) with ESMTPSA id 1B5E24C0282; Sat, 24 Jan 2015 12:33:08 -0600 (CST) Message-ID: <54C3E563.4070903@rice.edu> Date: Sat, 24 Jan 2015 12:33:07 -0600 From: Alan Cox User-Agent: Mozilla/5.0 (X11; FreeBSD i386; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: Konstantin Belousov , Ian Lepore Subject: Re: svn commit: r277643 - in head/sys: arm/arm dev/mem i386/i386 mips/mips sparc64/sparc64 References: <201501241251.t0OCpGa8053192@svn.freebsd.org> <1422111397.1038.53.camel@freebsd.org> <20150124154240.GV42409@kib.kiev.ua> In-Reply-To: <20150124154240.GV42409@kib.kiev.ua> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 suspectscore=3 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=7.0.1-1402240000 definitions=main-1501240198 Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 24 Jan 2015 18:33:10 -0000 On 01/24/2015 09:42, Konstantin Belousov wrote: > On Sat, Jan 24, 2015 at 07:56:37AM -0700, Ian Lepore wrote: >> On Sat, 2015-01-24 at 12:51 +0000, Konstantin Belousov wrote: >>> Author: kib >>> Date: Sat Jan 24 12:51:15 2015 >>> New Revision: 277643 >>> URL: https://svnweb.freebsd.org/changeset/base/277643 >>> >>> Log: >>> Remove Giant from /dev/mem and /dev/kmem. It is definitely not needed >>> for i386, and from the code inspection, nothing in the >>> arm/mips/sparc64 implementations depends on it. >>> >> I'm not sure I agree with that. On arm the memrw() implementation uses >> a single statically-allocated page of kva space into which it maps each >> physical page in turn in the main loop. What prevents preemption or >> multicore access to /dev/mem from trying to use that single page for >> multiple operations at once? > I see, thank you for noting this. > > But, I do not think that Giant is a solution for the problem. uiomove() > call accesses userspace, which may fault and cause sleep. If the > thread sleeps, the Giant is automatically dropped, so there is no real > protection. > > I think dump exclusive sx around whole memrw() should be enough. > > I can revert the commit for now, or I can leave it as is while > writing the patch with sx and waiting for somebody review. What > would you prefer ? > > P.S. mips uses uiomove_fromphys(), avoiding transient mapping, > and sparc allocates KVA when needed. > > While we're here, it's worth noting that the arm version of /dev/mem is not functionally equivalent to that of amd64 or i386. Arm disallows access to non-DRAM addresses through /dev/mem.