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 C0D0AC43387 for ; Thu, 10 Jan 2019 02:40:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 997FC2075C for ; Thu, 10 Jan 2019 02:40:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727005AbfAJCkX (ORCPT ); Wed, 9 Jan 2019 21:40:23 -0500 Received: from shelob.surriel.com ([96.67.55.147]:46080 "EHLO shelob.surriel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726425AbfAJCkW (ORCPT ); Wed, 9 Jan 2019 21:40:22 -0500 Received: from imladris.surriel.com ([96.67.55.152]) by shelob.surriel.com with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.91) (envelope-from ) id 1ghQGK-0005HJ-1E; Wed, 09 Jan 2019 21:40:04 -0500 Message-ID: <026dfd4c4f257a73063bd2f627cff5d7d4f17a60.camel@surriel.com> Subject: Re: [PATCH v3 0/5] kvm "virtio pmem" device From: Rik van Riel To: Dave Chinner , Pankaj Gupta Cc: 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@intel.com, nilal@redhat.com, kwolf@redhat.com, pbonzini@redhat.com, zwisler@kernel.org, vishal.l.verma@intel.com, dave.jiang@intel.com, david@redhat.com, jmoyer@redhat.com, xiaoguangrong.eric@gmail.com, hch@infradead.org, mst@redhat.com, jasowang@redhat.com, lcapitulino@redhat.com, imammedo@redhat.com, eblake@redhat.com, willy@infradead.org, tytso@mit.edu, adilger.kernel@dilger.ca, darrick.wong@oracle.com, rjw@rjwysocki.net Date: Wed, 09 Jan 2019 21:40:02 -0500 In-Reply-To: <20190110012617.GA4205@dastard> References: <20190109144736.17452-1-pagupta@redhat.com> <20190110012617.GA4205@dastard> Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-LQK7nuYVGuXcRCl7nOgd" X-Mailer: Evolution 3.28.5 (3.28.5-1.fc28) Mime-Version: 1.0 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Message-ID: <20190110024002.uRoBlEB0UukGCoDAHbhvc6Zsq6cHc-w6mpbYPRxEsFM@z> --=-LQK7nuYVGuXcRCl7nOgd Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2019-01-10 at 12:26 +1100, Dave Chinner wrote: > On Wed, Jan 09, 2019 at 08:17:31PM +0530, Pankaj Gupta wrote: > > This patch series has implementation for "virtio pmem".=20 > > "virtio pmem" is fake persistent memory(nvdimm) in guest=20 > > which allows to bypass the guest page cache. This also > > implements a VIRTIO based asynchronous flush mechanism. =20 >=20 > Hmmmm. Sharing the host page cache direct into the guest VM. Sounds > like a good idea, but..... >=20 > This means the guest VM can now run timing attacks to observe host > side page cache residency, and depending on the implementation I'm > guessing that the guest will be able to control host side page > cache eviction, too (e.g. via discard or hole punch operations). Even if the guest can only access its own disk image, using its own page cache pages, Pankaj's patches could still be a win because they allow the host kernel to easily evict page cache pages without doing IO. Evicting page cache pages that live inside a guest involves something like swapping, ballooning, or some sort of callback into the guest to figure out whether a page is clean. Evicting page cache pages that live in the host, OTOH... --=20 All Rights Reversed. --=-LQK7nuYVGuXcRCl7nOgd Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iQEzBAABCAAdFiEEKR73pCCtJ5Xj3yADznnekoTE3oMFAlw2sIIACgkQznnekoTE 3oMcsgf+NyjlTUYANTAxmyHg64xxfsGA+vKv5CRnV/QQ27Ph4mzP4N8MOIco/6P0 P13ign7T/4KhpY8OmuMPD3yTeKxHcEgYVBXeXjVPYEBfzFstweKo+IKIMvhqmzxG 3rLff6o0aOs36yVmI7ezNwwYjMJ9wt3Vl5FYunDM19dajj7FXwSfHoVzResayMF/ +xT2DyT8PC2nX0wSF9iYrznOvakWNFrIfPGmi4HiYdHPfefuIhMHPnvl0W4Pq3cP MJj07tJKuO34/wcsDOxWECwy+0U1zGFKi87+N2VONYB1SkeCCfmPtAlSk7pCFF2R MeDzTqwmnamGMBZBAvL5UdPjxyt5Xg== =t5QH -----END PGP SIGNATURE----- --=-LQK7nuYVGuXcRCl7nOgd--