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=-4.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 9A12CC433E3 for ; Thu, 30 Jul 2020 15:27:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 824C122BEF for ; Thu, 30 Jul 2020 15:27:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729762AbgG3P1N (ORCPT ); Thu, 30 Jul 2020 11:27:13 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:54880 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726275AbgG3P1N (ORCPT ); Thu, 30 Jul 2020 11:27:13 -0400 Received: from ip5f5af08c.dynamic.kabel-deutschland.de ([95.90.240.140] helo=wittgenstein) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1k1ASY-0005n8-GX; Thu, 30 Jul 2020 15:27:06 +0000 Date: Thu, 30 Jul 2020 17:27:05 +0200 From: Christian Brauner To: Matthew Wilcox 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: <20200730152705.ol42jppnl4xfhl32@wittgenstein> References: <1595869887-23307-1-git-send-email-anthony.yznaga@oracle.com> <20200730152250.GG23808@casper.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200730152250.GG23808@casper.infradead.org> 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 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. ;) > > To use this, you'd mshare() the anonymous memory range, essentially > detaching the VMA from the current process's mm_struct and reparenting > it to this new mm_struct, which has an fd referencing it. > > Then you call exec(), and the exec'ed task gets to call mmap() on that > new fd to attach the memory range to its own address space. > > Presto!