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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,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 359CDC5DF63 for ; Wed, 6 Nov 2019 05:58:34 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D17A82075C for ; Wed, 6 Nov 2019 05:58:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ozlabs.org header.i=@ozlabs.org header.b="CYz/tUuX" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D17A82075C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=ozlabs.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 8F1E86B0010; Wed, 6 Nov 2019 00:58:32 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 8C7A86B0266; Wed, 6 Nov 2019 00:58:32 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7B79A6B0269; Wed, 6 Nov 2019 00:58:32 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0110.hostedemail.com [216.40.44.110]) by kanga.kvack.org (Postfix) with ESMTP id 4E3616B0266 for ; Wed, 6 Nov 2019 00:58:32 -0500 (EST) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with SMTP id EDA3C181AEF0B for ; Wed, 6 Nov 2019 05:58:31 +0000 (UTC) X-FDA: 76124798022.15.bread02_84a374b185050 X-HE-Tag: bread02_84a374b185050 X-Filterd-Recvd-Size: 4158 Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) by imf26.hostedemail.com (Postfix) with ESMTP for ; Wed, 6 Nov 2019 05:58:31 +0000 (UTC) Received: by ozlabs.org (Postfix, from userid 1003) id 477G6q4LWfz9sPv; Wed, 6 Nov 2019 16:58:27 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ozlabs.org; s=201707; t=1573019907; bh=qi+bi8MVZoNDV18JpOPasJiz17z6ctI9/w/JfB9116Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=CYz/tUuXCmy6vBZ6hJN1l6iLFQ0ubQUmYKLik3gSraoou1tPe7wu+yYwuJ8fD9jbX c31BBrd+vXDBwWO19GvgVFQtA0hLdcCK+jkpdcRHH/z/UPpMziyXFvT/le5vMTpowQ Mt91jTijH39WVp8VweQDXJiLsC7A1b9qxURh0mlK4Ksldg6v3iPNPNmaXummCzs664 DAVi66wTllKw/ok+EJVMgVRKAnG6o2i9bdX9pKTGAsb9EIrb8twFuiqyeTxNS0SZaH oCoS6kJZaBQidJAeF5lvSopmrhFJqzTUQ0qLoosonMQFbse4NlGr4riXisiWaDPQtg 50iFa8T/7W67w== Date: Wed, 6 Nov 2019 15:52:38 +1100 From: Paul Mackerras To: Bharata B Rao Cc: linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org, linux-mm@kvack.org, paulus@au1.ibm.com, aneesh.kumar@linux.vnet.ibm.com, jglisse@redhat.com, cclaudio@linux.ibm.com, linuxram@us.ibm.com, sukadev@linux.vnet.ibm.com, hch@lst.de Subject: Re: [PATCH v10 3/8] KVM: PPC: Shared pages support for secure guests Message-ID: <20191106045238.GD12069@oak.ozlabs.ibm.com> References: <20191104041800.24527-1-bharata@linux.ibm.com> <20191104041800.24527-4-bharata@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191104041800.24527-4-bharata@linux.ibm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Nov 04, 2019 at 09:47:55AM +0530, Bharata B Rao wrote: > A secure guest will share some of its pages with hypervisor (Eg. virtio > bounce buffers etc). Support sharing of pages between hypervisor and > ultravisor. > > Shared page is reachable via both HV and UV side page tables. Once a > secure page is converted to shared page, the device page that represents > the secure page is unmapped from the HV side page tables. I'd like to understand a little better what's going on - see below... > +/* > + * Shares the page with HV, thus making it a normal page. > + * > + * - If the page is already secure, then provision a new page and share > + * - If the page is a normal page, share the existing page > + * > + * In the former case, uses dev_pagemap_ops.migrate_to_ram handler > + * to unmap the device page from QEMU's page tables. > + */ > +static unsigned long > +kvmppc_share_page(struct kvm *kvm, unsigned long gpa, unsigned long page_shift) > +{ > + > + int ret = H_PARAMETER; > + struct page *uvmem_page; > + struct kvmppc_uvmem_page_pvt *pvt; > + unsigned long pfn; > + unsigned long gfn = gpa >> page_shift; > + int srcu_idx; > + unsigned long uvmem_pfn; > + > + srcu_idx = srcu_read_lock(&kvm->srcu); > + mutex_lock(&kvm->arch.uvmem_lock); > + if (kvmppc_gfn_is_uvmem_pfn(gfn, kvm, &uvmem_pfn)) { > + uvmem_page = pfn_to_page(uvmem_pfn); > + pvt = uvmem_page->zone_device_data; > + pvt->skip_page_out = true; > + } > + > +retry: > + mutex_unlock(&kvm->arch.uvmem_lock); > + pfn = gfn_to_pfn(kvm, gfn); At this point, pfn is the value obtained from the page table for userspace (e.g. QEMU), right? I would think it should be equal to uvmem_pfn in most cases, shouldn't it? If not, what is it going to be? > + if (is_error_noslot_pfn(pfn)) > + goto out; > + > + mutex_lock(&kvm->arch.uvmem_lock); > + if (kvmppc_gfn_is_uvmem_pfn(gfn, kvm, &uvmem_pfn)) { > + uvmem_page = pfn_to_page(uvmem_pfn); > + pvt = uvmem_page->zone_device_data; > + pvt->skip_page_out = true; > + kvm_release_pfn_clean(pfn); This is going to do a put_page(), unless pfn is a reserved pfn. If it does a put_page(), where did we do the corresponding get_page()? However, since kvmppc_gfn_is_uvmem_pfn() returned true, doesn't that mean that pfn here should be a device pfn, and in fact should be the same as uvmem_pfn (possibly with some extra bit(s) set)? What does kvm_is_reserved_pfn() return for a device pfn? Paul.