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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=unavailable 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 C6FE7C43612 for ; Mon, 14 Jan 2019 07:15:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A06D620659 for ; Mon, 14 Jan 2019 07:15:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726582AbfANHPo (ORCPT ); Mon, 14 Jan 2019 02:15:44 -0500 Received: from mx1.redhat.com ([209.132.183.28]:37780 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726067AbfANHPn (ORCPT ); Mon, 14 Jan 2019 02:15:43 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 62E8189ACA; Mon, 14 Jan 2019 07:15:43 +0000 (UTC) Received: from colo-mx.corp.redhat.com (colo-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.21]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1722418C40; Mon, 14 Jan 2019 07:15:43 +0000 (UTC) Received: from zmail21.collab.prod.int.phx2.redhat.com (zmail21.collab.prod.int.phx2.redhat.com [10.5.83.24]) by colo-mx.corp.redhat.com (Postfix) with ESMTP id 3BE303F7CB; Mon, 14 Jan 2019 07:15:41 +0000 (UTC) Date: Mon, 14 Jan 2019 02:15:40 -0500 (EST) From: Pankaj Gupta To: Matthew Wilcox Cc: Dave Chinner , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, qemu-devel@nongnu.org, linux-nvdimm@ml01.01.org, linux-fsdevel@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-acpi@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, jack@suse.cz, stefanha@redhat.com, dan j williams , riel@surriel.com, nilal@redhat.com, kwolf@redhat.com, pbonzini@redhat.com, zwisler@kernel.org, vishal l verma , dave jiang , david@redhat.com, jmoyer@redhat.com, xiaoguangrong eric , hch@infradead.org, mst@redhat.com, jasowang@redhat.com, lcapitulino@redhat.com, imammedo@redhat.com, eblake@redhat.com, tytso@mit.edu, adilger kernel , darrick wong , rjw@rjwysocki.net Message-ID: <942065073.64011540.1547450140670.JavaMail.zimbra@redhat.com> In-Reply-To: <20190113233820.GX6310@bombadil.infradead.org> References: <20190109144736.17452-1-pagupta@redhat.com> <20190110012617.GA4205@dastard> <1326478078.61913951.1547192704870.JavaMail.zimbra@redhat.com> <20190113232902.GD4205@dastard> <20190113233820.GX6310@bombadil.infradead.org> Subject: Re: [PATCH v3 0/5] kvm "virtio pmem" device MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [10.65.161.12, 10.4.195.26] Thread-Topic: kvm "virtio pmem" device Thread-Index: fXKA+vj/EtBojiKZdg45HpfkQoxS7w== X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Mon, 14 Jan 2019 07:15:43 +0000 (UTC) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Message-ID: <20190114071540.qMIRPRhSeAPkq0JpakkzARC8s93KAD_ofwfjc0_k5LQ@z> > > Until you have images (and hence host page cache) shared between > > multiple guests. People will want to do this, because it means they > > only need a single set of pages in host memory for executable > > binaries rather than a set of pages per guest. Then you have > > multiple guests being able to detect residency of the same set of > > pages. If the guests can then, in any way, control eviction of the > > pages from the host cache, then we have a guest-to-guest information > > leak channel. > > I don't think we should ever be considering something that would allow a > guest to evict page's from the host's pagecache [1]. The guest should > be able to kick its own references to the host's pagecache out of its > own pagecache, but not be able to influence whether the host or another > guest has a read-only mapping cached. > > [1] Unless the guest is allowed to modify the host's file; obviously > truncation, holepunching, etc are going to evict pages from the host's > page cache. This is so correct. Guest does not not evict host page cache pages directly. In case of virtio-pmem & DAX, guest clears guest page cache exceptional entries. Its solely decision of host to take action on the host page cache pages. In case of virtio-pmem, guest does not modify host file directly i.e don't perform hole punch & truncation operation directly on host file. Thanks, Pankaj