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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_2 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 D0552C43331 for ; Tue, 24 Mar 2020 17:56:03 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A18272074D for ; Tue, 24 Mar 2020 17:56:03 +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="aPgsNEW+" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A18272074D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1jGnlp-0002RQ-5Z; Tue, 24 Mar 2020 17:55:21 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1jGnln-0002RK-I4 for xen-devel@lists.xenproject.org; Tue, 24 Mar 2020 17:55:19 +0000 X-Inumbo-ID: 9bc447f6-6df8-11ea-b34e-bc764e2007e4 Received: from merlin.infradead.org (unknown [2001:8b0:10b:1231::1]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 9bc447f6-6df8-11ea-b34e-bc764e2007e4; Tue, 24 Mar 2020 17:55:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=Mime-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=x7j/6aszmsQw+zkzHTKU7xJL9Tegorc3I2ejQAv9KRA=; b=aPgsNEW+lA+3hrhA/4l+JnNYTR XCs81x5uJb8wPBC27K4fDvrJ4Tu7MtxCs9izWndi4vUpYPnJ9YnbXKql7VzjvUjtZOA05vNbmfVVk aPEQOb+YLIBSz9Rp2kuRIRPThPL20CXYbx2wAJnmWspqZVs9kOjpQkaUlRQEsZh8KBafuUanpcllU wNq932KjpP7K86Mg26m3mCZs8+C0ohu3r68rdkwIMvHMJ2sPvGGDDhyAZoj9vzVQ6nQYZ1Ta3XcCq DyvUqoUbodgZ/9voLxGf0ImQ94yl4UyKupzUCNyr5iPiaMx0bXrBh9MQ0n4sxWT8yjQvpdqqZ59et KqurAdlw==; Received: from 54-240-197-225.amazon.com ([54.240.197.225] helo=u3832b3a9db3152.ant.amazon.com) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jGnla-0000SO-Qs; Tue, 24 Mar 2020 17:55:07 +0000 Message-ID: <21a867b0a394c7ccee2f1c5d10e367905f30174e.camel@infradead.org> From: David Woodhouse To: Julien Grall , paul@xen.org, xen-devel@lists.xenproject.org Date: Tue, 24 Mar 2020 17:55:04 +0000 In-Reply-To: <8efd11af-7603-c823-62db-468f07a49790@xen.org> References: <759b48cc361af1136e3cf1658f3dcb1d2937db9c.camel@infradead.org> <20200319212150.2651419-1-dwmw2@infradead.org> <20200319212150.2651419-2-dwmw2@infradead.org> <004701d5febc$3632bfe0$a2983fa0$@xen.org> <45c147a12565cb1b0ca34217a8d66289a91ec35c.camel@infradead.org> <3018bb93-b79c-9182-30cc-364fb59ec2fd@xen.org> <8efd11af-7603-c823-62db-468f07a49790@xen.org> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-W2JqeeO3aZ0bZLdOj7yi" X-Mailer: Evolution 3.28.5-0ubuntu0.18.04.1 Mime-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by merlin.infradead.org. See http://www.infradead.org/rpr.html Subject: Re: [Xen-devel] [PATCH 2/2] xen/mm: Introduce PGC_state_uninitialised X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: 'Stefano Stabellini' , 'Wei Liu' , 'Andrew Cooper' , 'Ian Jackson' , 'George Dunlap' , hongyxia@amazon.com, 'Jan Beulich' , 'Volodymyr Babchuk' , 'Roger Pau =?ISO-8859-1?Q?Monn=E9=27?= Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" --=-W2JqeeO3aZ0bZLdOj7yi Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, 2020-03-24 at 10:08 +0000, Julien Grall wrote: > Hi David, >=20 > On 23/03/2020 10:55, David Woodhouse wrote: > > On Mon, 2020-03-23 at 09:34 +0000, Julien Grall wrote: > > > For liveupdate, we will need a way to initialize a page but mark it a= s > > > already inuse (i.e in the same state as they would be if allocated > > > normally). > >=20 > > I am unconvinced of the veracity of this claim. > >=20 > > We don't want to turn specific details of the current Xen buddy > > allocator part into of the implicit ABI of live update. That goes for > > the power-of-two zone boundaries, amongst other things. >=20 > Why would you to do that? Marking the page as already used is no=20 > different to "PGC_state_unitialized" except the "struct page_info" and= =20 > the internal of the buddy allocator would be properly setup for start=20 > rather than at free. The internals of the buddy allocator *cannot* be set up properly for a page which it would not actually give out =E2=80=94 like the zero page. We *could* do some tricks to allocate the zone structures for zones which *do* exist but contain only "pre-allocated" pages so the buddy allocator has never seen those zones... yet. > I think using "PGC_state_unitialised" for preserved page is an abuse. I= =20 > understand this is existing in other part of Xen (particularly on x86),= =20 > but I would rather not try to add more. I am perfectly happy to try avoiding PGC_state_uninitialised for pages which are "in use" at boot time due to live update. All I insist on is that you explicitly describe the ABI constraints that it imposes, if any. For example, that hack which stops the buddy allocator from giving out page zero: Could we have live updated from a Xen without that hack, to a Xen which has it? With page zero already given out to a domain? With PGC_state_initialised and passing the page through init_heap_pages() if/when it ever gets freed, my answer would be 'yes'. What's yours? 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