From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757452Ab3EGLiW (ORCPT ); Tue, 7 May 2013 07:38:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:20448 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756225Ab3EGLiV (ORCPT ); Tue, 7 May 2013 07:38:21 -0400 Date: Tue, 7 May 2013 13:38:10 +0200 From: Andrew Jones To: Andrea Arcangeli Cc: qemu-devel@nongnu.org, linux-kernel@vger.kernel.org, Anthony Liguori , Orit Wasserman , Juan Quintela , Hugh Dickins , Isaku Yamahata , Mel Gorman , Paolo Bonzini Subject: Re: [Qemu-devel] [PATCH 0/4] madvise(MADV_USERFAULT) & sys_remap_anon_pages() Message-ID: <20130507113809.GB10720@hawk.usersys.redhat.com> References: <1367870221-12676-1-git-send-email-aarcange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1367870221-12676-1-git-send-email-aarcange@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 06, 2013 at 09:56:57PM +0200, Andrea Arcangeli wrote: > > The current behavior of remap_anon_pages is very strict to avoid any > chance of memory corruption going unnoticed, and it will return > -EFAULT at the first sign of something unexpected (like a page already > mapped in the destination pmd/pte, potentially signaling an userland > thread race condition with two threads userfaulting on the same > destination address). mremap is not strict like that: it would drop > the destination range silently and it would succeed in such a > condition. So on the API side, I wonder if I should add a flag to > remap_anon_pages to provide non-strict behavior more similar to > mremap. OTOH not providing the permissive mremap behavior may actually > be better to force userland to be strict and be sure it knows what it > is doing (otherwise it should use mremap in the first place?). > What about instead of adding a new syscall (remap_anon_pages) to instead extend mremap with new flags giving it a strict mode? drew