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 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 6B9E6C43334 for ; Thu, 21 Jul 2022 09:57:43 +0000 (UTC) Received: from localhost ([::1]:52288 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oESwA-0002jQ-Ca for qemu-devel@archiver.kernel.org; Thu, 21 Jul 2022 05:57:42 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:35102) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oESul-0001fw-A2 for qemu-devel@nongnu.org; Thu, 21 Jul 2022 05:56:15 -0400 Received: from dfw.source.kernel.org ([139.178.84.217]:54348) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oESuj-0003r0-LK for qemu-devel@nongnu.org; Thu, 21 Jul 2022 05:56:14 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id A6DF861F85; Thu, 21 Jul 2022 09:56:10 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AE75DC3411E; Thu, 21 Jul 2022 09:56:09 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="luphDUn9" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1658397368; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=qAC4OHlb5nESn/hQljIdm76lzbXXkrEH8eFVs/QY/to=; b=luphDUn9Y0Z5BanOIxutoz+pGsTweEr9t0ksBqG8z42+VlhNZimvLypLYk2EEmibXCfKjr KonL9nRzGAXK3czCSySlRd2/H5BiWptRZ70jkHjWqn8E9VUFWjsCTPb+OM7TobIuWpIQKr MwWOqB9ZrCHWm+MACSRiAV+8YVorTxk= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 48b80d1c (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Thu, 21 Jul 2022 09:56:08 +0000 (UTC) Date: Thu, 21 Jul 2022 11:56:06 +0200 From: "Jason A. Donenfeld" To: Paolo Bonzini Cc: qemu-devel@nongnu.org Subject: Re: [PATCH resend v3] hw/i386: pass RNG seed via setup_data entry Message-ID: References: <20220711145432.56704-1-Jason@zx2c4.com> <20220719115300.104095-1-Jason@zx2c4.com> <06e60181-2f77-6f02-5015-fd14153efff3@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Received-SPF: pass client-ip=139.178.84.217; envelope-from=SRS0=2GtW=X2=zx2c4.com=Jason@kernel.org; helo=dfw.source.kernel.org X-Spam_score_int: -67 X-Spam_score: -6.8 X-Spam_bar: ------ X-Spam_report: (-6.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, HEADER_FROM_DIFFERENT_DOMAINS=0.249, RCVD_IN_DNSWL_HI=-5, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hey again, On Thu, Jul 21, 2022 at 11:47:29AM +0200, Jason A. Donenfeld wrote: > Hi Paolo, > > Thanks for your review. > > On Thu, Jul 21, 2022 at 11:19:40AM +0200, Paolo Bonzini wrote: > > The issue with live migration is that the setup data changes from before > > to after the patches. This means that a live migration exactly _in the > > middle_ of reading the Linux boot data could fail badly. For example, > > you could migrate in the middle of reading the DTB, and it would be > > shifted by the ~50 bytes of the setup_data and seed. The size would > > also not match so, even though probably things would mostly work if you > > place the seed last, that's not really optimal either. > > This doesn't really make sense to me, as I don't think the machine can > even be migrated during x86_load_linux(), and a migration will skip this > whole step anyway since this is mutable memory that a live kernel does > mutate. > > However, what I'll do is reverse the order of these, so that the DTB is > added first, and I'll only set up the links in the right order so that > there's no potential race. I'll send a v+1 doing this shortly. As I implement the "race-free" version, I notice that this is even more of a non-issue, seeing as even without this patch, the DTB is loaded after the length is written. What you're talking about is just not real. I'll still send a v+1 changing the order, because that seems better anyway, but the race thing seems pretty imaginary... Jason