From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CEBB7C433E0 for ; Thu, 30 Jul 2020 15:34:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AB7BE20838 for ; Thu, 30 Jul 2020 15:34:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="dCzn/wkP" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729745AbgG3Pey (ORCPT ); Thu, 30 Jul 2020 11:34:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37060 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726581AbgG3Pex (ORCPT ); Thu, 30 Jul 2020 11:34:53 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6D164C061574; Thu, 30 Jul 2020 08:34:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=VBPWwrsXMPKnDitP89rUNPyQKT9bsGFBjZQdtzzU7ds=; b=dCzn/wkP++dkRu1oDJt9RGaBFz K2yUeZF7hHvMOL2NmgXDAC5Z4QNx8FMnirqGBK+cSaN/08vTSc9ttNWOCGRYDQyNvT9Ez//mrHUnt n0eUNrEFNhpwEIb5zx6moVr+SseapOElItdDhZy5VeFs8+NeRxLvC53Bugwg+M10AxEdv9YTV6tc6 0oa6hy8yD+sLiFfg484wsbw6RQbkY2AFSGHwMz8757ejFlLk0zDqtX9+6o8MNNhFPJKQpvOkTFAMi YyvPWknL1/EsDgV5cQaPJ0mtm/1cVNunmLlH8j3dnt9H+/6ynBG4D8QMl4l0ZfckxU+qysqDoBqka jA9bb4VQ==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1k1Aa2-0006vP-4Q; Thu, 30 Jul 2020 15:34:50 +0000 Date: Thu, 30 Jul 2020 16:34:50 +0100 From: Matthew Wilcox To: Christian Brauner Cc: Anthony Yznaga , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, mhocko@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, arnd@arndb.de, ebiederm@xmission.com, keescook@chromium.org, gerg@linux-m68k.org, ktkhai@virtuozzo.com, peterz@infradead.org, esyr@redhat.com, jgg@ziepe.ca, christian@kellner.me, areber@redhat.com, cyphar@cyphar.com, steven.sistare@oracle.com Subject: Re: [RFC PATCH 0/5] madvise MADV_DOEXEC Message-ID: <20200730153450.GH23808@casper.infradead.org> References: <1595869887-23307-1-git-send-email-anthony.yznaga@oracle.com> <20200730152250.GG23808@casper.infradead.org> <20200730152705.ol42jppnl4xfhl32@wittgenstein> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200730152705.ol42jppnl4xfhl32@wittgenstein> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Jul 30, 2020 at 05:27:05PM +0200, Christian Brauner wrote: > On Thu, Jul 30, 2020 at 04:22:50PM +0100, Matthew Wilcox wrote: > > On Mon, Jul 27, 2020 at 10:11:22AM -0700, Anthony Yznaga wrote: > > > This patchset adds support for preserving an anonymous memory range across > > > exec(3) using a new madvise MADV_DOEXEC argument. The primary benefit for > > > sharing memory in this manner, as opposed to re-attaching to a named shared > > > memory segment, is to ensure it is mapped at the same virtual address in > > > the new process as it was in the old one. An intended use for this is to > > > preserve guest memory for guests using vfio while qemu exec's an updated > > > version of itself. By ensuring the memory is preserved at a fixed address, > > > vfio mappings and their associated kernel data structures can remain valid. > > > In addition, for the qemu use case, qemu instances that back guest RAM with > > > anonymous memory can be updated. > > > > I just realised that something else I'm working on might be a suitable > > alternative to this. Apologies for not realising it sooner. > > > > http://www.wil.cx/~willy/linux/sileby.html > > Just skimming: make it O_CLOEXEC by default. ;) I appreciate the suggestion, and it makes sense for many 'return an fd' interfaces, but the point of mshare() is to, well, share. So sharing the fd with a child is a common usecase, unlike say sharing a timerfd. The only other reason to use mshare() is to pass the fd over a unix socket to a non-child, and I submit that is far less common than wanting to share with a child.