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=-3.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 E5A49C54FCB for ; Fri, 24 Apr 2020 12:38:06 +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 B504720700 for ; Fri, 24 Apr 2020 12:38:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=citrix.com header.i=@citrix.com header.b="Gg8clwlb" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B504720700 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=citrix.com 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 4.92) (envelope-from ) id 1jRxaM-0002pp-Ej; Fri, 24 Apr 2020 12:37:38 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jRxaK-0002pk-VU for xen-devel@lists.xenproject.org; Fri, 24 Apr 2020 12:37:37 +0000 X-Inumbo-ID: 5fb1fbef-8628-11ea-9491-12813bfff9fa Received: from esa4.hc3370-68.iphmx.com (unknown [216.71.155.144]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 5fb1fbef-8628-11ea-9491-12813bfff9fa; Fri, 24 Apr 2020 12:37:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=citrix.com; s=securemail; t=1587731855; h=date:from:to:cc:subject:message-id:references: mime-version:content-transfer-encoding:in-reply-to; bh=bUIuip07xZMkH6foTuXX1izTHbky8gMaULlT4Ws10HI=; b=Gg8clwlbe+Rt/iSaYnDA2QjMFHVTP2SPJQ0n1L8R6oB5mewXtHfbvL5M FsBml9LcG3BX3TuoZrOFfWkl6sWqemdoVMYfTN9J7L/VT0egiMGSyjYb9 0hJcysnYGCr1Dohp9P9tzFDjBV+7XOcaWulqH/8vUFi30hU6HT/D18g/B 8=; Authentication-Results: esa4.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none; spf=None smtp.pra=roger.pau@citrix.com; spf=Pass smtp.mailfrom=roger.pau@citrix.com; spf=None smtp.helo=postmaster@mail.citrix.com Received-SPF: None (esa4.hc3370-68.iphmx.com: no sender authenticity information available from domain of roger.pau@citrix.com) identity=pra; client-ip=162.221.158.21; receiver=esa4.hc3370-68.iphmx.com; envelope-from="roger.pau@citrix.com"; x-sender="roger.pau@citrix.com"; x-conformance=sidf_compatible Received-SPF: Pass (esa4.hc3370-68.iphmx.com: domain of roger.pau@citrix.com designates 162.221.158.21 as permitted sender) identity=mailfrom; client-ip=162.221.158.21; receiver=esa4.hc3370-68.iphmx.com; envelope-from="roger.pau@citrix.com"; x-sender="roger.pau@citrix.com"; x-conformance=sidf_compatible; x-record-type="v=spf1"; x-record-text="v=spf1 ip4:209.167.231.154 ip4:178.63.86.133 ip4:195.66.111.40/30 ip4:85.115.9.32/28 ip4:199.102.83.4 ip4:192.28.146.160 ip4:192.28.146.107 ip4:216.52.6.88 ip4:216.52.6.188 ip4:162.221.158.21 ip4:162.221.156.83 ip4:168.245.78.127 ~all" Received-SPF: None (esa4.hc3370-68.iphmx.com: no sender authenticity information available from domain of postmaster@mail.citrix.com) identity=helo; client-ip=162.221.158.21; receiver=esa4.hc3370-68.iphmx.com; envelope-from="roger.pau@citrix.com"; x-sender="postmaster@mail.citrix.com"; x-conformance=sidf_compatible IronPort-SDR: bFtQ2m+JSaQEX8TLGR5FuMnhmmn91opAFbAqj3f8dRMCDt6Kd80FYoJE49jrC0rpC2PAyQ1o+E oRD7Yowc8pLTFMPKU14hRQO5VwxV+dbhLTwg35QnbACShjM+ezwlVWY0A9CJuKJ7MuEVBlOs0q wIzSl7q+31TIqwWFgRspxGNqVeN/j0O434YlJ3lnt1Ss2IncEjjMtOH/JcrAaoV9BOUUaZMsDG NbJvKYw8VTrtS1UpS1G7HnG99ah1pjO94lGOdTvpQzXRerFxqDL//1BNYjKcKB0yD/A78DVvdj SNg= X-SBRS: 2.7 X-MesageID: 16882065 X-Ironport-Server: esa4.hc3370-68.iphmx.com X-Remote-IP: 162.221.158.21 X-Policy: $RELAYED X-IronPort-AV: E=Sophos;i="5.73,311,1583211600"; d="scan'208";a="16882065" Date: Fri, 24 Apr 2020 14:37:28 +0200 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Tamas K Lengyel Subject: Re: [PATCH v17 1/2] mem_sharing: fix sharability check during fork reset Message-ID: <20200424123728.GI28601@Air-de-Roger> References: <70ea4889e30ed35760329331ddfeb279fcd80786.1587655725.git.tamas.lengyel@intel.com> <20200424094343.GH28601@Air-de-Roger> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-ClientProxiedBy: AMSPEX02CAS01.citrite.net (10.69.22.112) To AMSPEX02CL02.citrite.net (10.69.22.126) X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Tamas K Lengyel , Wei Liu , Andrew Cooper , George Dunlap , Jan Beulich , Xen-devel Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On Fri, Apr 24, 2020 at 06:18:24AM -0600, Tamas K Lengyel wrote: > On Fri, Apr 24, 2020 at 3:44 AM Roger Pau Monné wrote: > > > > On Thu, Apr 23, 2020 at 08:30:06AM -0700, Tamas K Lengyel wrote: > > > When resetting a VM fork we ought to only remove pages that were allocated for > > > the fork during it's execution and the contents copied over from the parent. > > > This can be determined if the page is sharable as special pages used by the > > > fork for other purposes will not pass this test. Unfortunately during the fork > > > reset loop we only partially check whether that's the case. A page's type may > > > indicate it is sharable (pass p2m_is_sharable) but that's not a sufficient > > > check by itself. All checks that are normally performed before a page is > > > converted to the sharable type need to be performed to avoid removing pages > > > from the p2m that may be used for other purposes. For example, currently the > > > reset loop also removes the vcpu info pages from the p2m, potentially putting > > > the guest into infinite page-fault loops. > > > > > > Signed-off-by: Tamas K Lengyel > > > > Reviewed-by: Roger Pau Monné > > Thanks! > > > > > I've been looking however and I'm not able to spot where you copy the > > shared_info data, which I think it's also quite critical for the > > domain, as it contains the info about event channels (when using L2). > > Also for HVM forks the shared info should be mapped at the same gfn as > > the parent, or else the child trying to access it will trigger an EPT > > fault that won't be able to populate such gfn, because the shared_info > > on the parent is already shared between Xen and the parent. > > Pages that cause an EPT fault but can't be made shared get a new page > allocated for them and copied in mem_sharing_fork_page. There are many > pages like that, mostly due to QEMU mapping them and thus holding an > extra reference. That said, shared_info is manually copied during > forking in copy_special_pages, at the end of the function you will > find: > > old_mfn = _mfn(virt_to_mfn(d->shared_info)); > new_mfn = _mfn(virt_to_mfn(cd->shared_info)); > > copy_domain_page(new_mfn, old_mfn); Oh, sorry for the noise, I somehow missed it. Roger.