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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 CD09FC433E0 for ; Tue, 7 Jul 2020 08:07:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AC629206E2 for ; Tue, 7 Jul 2020 08:07:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725941AbgGGIHa (ORCPT ); Tue, 7 Jul 2020 04:07:30 -0400 Received: from jabberwock.ucw.cz ([46.255.230.98]:57494 "EHLO jabberwock.ucw.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725874AbgGGIHa (ORCPT ); Tue, 7 Jul 2020 04:07:30 -0400 Received: by jabberwock.ucw.cz (Postfix, from userid 1017) id 2E0741C0C0E; Tue, 7 Jul 2020 10:07:27 +0200 (CEST) Date: Tue, 7 Jul 2020 10:07:26 +0200 From: Pavel Machek To: Michal Hocko Cc: Jann Horn , "Catangiu, Adrian Costin" , "linux-mm@kvack.org" , "linux-pm@vger.kernel.org" , "virtualization@lists.linux-foundation.org" , "linux-api@vger.kernel.org" , "akpm@linux-foundation.org" , "rjw@rjwysocki.net" , "len.brown@intel.com" , "fweimer@redhat.com" , "keescook@chromium.org" , "luto@amacapital.net" , "wad@chromium.org" , "mingo@kernel.org" , "bonzini@gnu.org" , "Graf (AWS), Alexander" , "MacCarthaigh, Colm" , "Singh, Balbir" , "Sandu, Andrei" , "Brooker, Marc" , "Weiss, Radu" , "Manwaring, Derek" Subject: Re: [RFC]: mm,power: introduce MADV_WIPEONSUSPEND Message-ID: <20200707080726.GA32357@amd> References: <20200703113026.GT18446@dhcp22.suse.cz> <20200707073823.GA3820@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="LQksG6bCIzRHxTLp" Content-Disposition: inline In-Reply-To: <20200707073823.GA3820@dhcp22.suse.cz> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-api-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org --LQksG6bCIzRHxTLp Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi! > > > > This patch adds logic to the kernel power code to zero out contents= of > > > > all MADV_WIPEONSUSPEND VMAs present in the system during its transi= tion > > > > to any suspend state equal or greater/deeper than Suspend-to-memory, > > > > known as S3. > > > > > > How does the application learn that its memory got wiped? S2disk is an > > > async operation and it can happen at any time during the task executi= on. > > > So how does the application work to prevent from corrupted state - e.= g. > > > when suspended between two memory loads? > >=20 > > You can do it seqlock-style, kind of - you reserve the first byte of > > the page or so as a "is this page initialized" marker, and after every > > read from the page, you do a compiler barrier and check whether that > > byte has been cleared. >=20 > This is certainly possible yet wery awkwar interface to use IMHO. > MADV_EXTERNALY_VOLATILE would express the actual semantic much better. > I might not still understand the expected usecase but if the target > application has to be changed anyway then why not simply use a > transparent and proper signaling mechanism like poll on a fd. That The goal is to have cryprographically-safe get_random_number() with 0 syscalls. You'd need to do: if (!poll(did_i_migrate)) { use_prng_seed(); if (poll(did_i_migrate)) { /* oops_they_migrated_me_in_middle_of_computation, lets_redo_it() */ goto retry: } } Which means two syscalls.. Best regards, Pavel --=20 (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo= g.html --LQksG6bCIzRHxTLp Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iEYEARECAAYFAl8ELT4ACgkQMOfwapXb+vLyMACgqbe6zmXiEEz8DaabrD2NC2vV 5xgAn3dKno+G4UTAHEY2WCnK1mXkOj/5 =rQsH -----END PGP SIGNATURE----- --LQksG6bCIzRHxTLp--