From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Williams Subject: Re: [PATCH v3 0/5] kvm "virtio pmem" device Date: Sat, 12 Jan 2019 17:43:26 -0800 Message-ID: References: <20190109144736.17452-1-pagupta@redhat.com> <20190110012617.GA4205@dastard> <20190110101757.GC15790@quack2.suse.cz> <1354249849.63357171.1547343519970.JavaMail.zimbra@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Jan Kara , KVM list , David Hildenbrand , linux-nvdimm , Jason Wang , Dave Chinner , Qemu Developers , virtualization-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, adilger kernel , Ross Zwisler , Eric Blake , darrick wong , "Michael S. Tsirkin" , Matthew Wilcox , Christoph Hellwig , Linux ACPI , linux-ext4 , Rik van Riel , Stefan Hajnoczi , Igor Mammedov , lcapitulino-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, Kevin Wolf , Nitesh Narayan Lal , Theodore Ts'o , xiaoguangro To: Pankaj Gupta Return-path: In-Reply-To: <1354249849.63357171.1547343519970.JavaMail.zimbra-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org Sender: "Linux-nvdimm" List-Id: linux-fsdevel.vger.kernel.org On Sat, Jan 12, 2019 at 5:38 PM Pankaj Gupta wrote: > > > > > > > On Thu 10-01-19 12:26:17, Dave Chinner wrote: > > > On Wed, Jan 09, 2019 at 08:17:31PM +0530, Pankaj Gupta wrote: > > > > This patch series has implementation for "virtio pmem". > > > > "virtio pmem" is fake persistent memory(nvdimm) in guest > > > > which allows to bypass the guest page cache. This also > > > > implements a VIRTIO based asynchronous flush mechanism. > > > > > > Hmmmm. Sharing the host page cache direct into the guest VM. Sounds > > > like a good idea, but..... > > > > > > 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). > > > > > > Which means this functionality looks to me like a new vector for > > > information leakage into and out of the guest VM via guest > > > controlled host page cache manipulation. > > > > > > https://arxiv.org/pdf/1901.01161 > > > > > > I might be wrong, but if I'm not we're going to have to be very > > > careful about how guest VMs can access and manipulate host side > > > resources like the page cache..... > > > > Right. Thinking about this I would be more concerned about the fact that > > guest can effectively pin amount of host's page cache upto size of the > > device/file passed to guest as PMEM, can't it Pankaj? Or is there some QEMU > > magic that avoids this? > > Yes, guest will pin these host page cache pages using 'get_user_pages' by > elevating the page reference count. But these pages can be reclaimed by host > at any time when there is memory pressure. Wait, how can the guest pin the host pages? I would expect this to happen only when using vfio and device assignment. Otherwise, no the host can't reclaim a pinned page, that's the whole point of a pin to prevent the mm from reclaiming ownership. > KVM does not permanently pin pages. vfio does that but we are not using > it here. Right, so I'm confused by your pin assertion above. 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=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED 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 02E6FC43387 for ; Sun, 13 Jan 2019 01:43:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BD6E620836 for ; Sun, 13 Jan 2019 01:43:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=intel-com.20150623.gappssmtp.com header.i=@intel-com.20150623.gappssmtp.com header.b="k2ZeoyA4" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726622AbfAMBnj (ORCPT ); Sat, 12 Jan 2019 20:43:39 -0500 Received: from mail-ot1-f66.google.com ([209.85.210.66]:42531 "EHLO mail-ot1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726477AbfAMBni (ORCPT ); Sat, 12 Jan 2019 20:43:38 -0500 Received: by mail-ot1-f66.google.com with SMTP id v23so16463350otk.9 for ; Sat, 12 Jan 2019 17:43:37 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=12pdMTxqi83EEHwmbAWeg9wmewWbN2jswxBvTfN4Tx4=; b=k2ZeoyA4j1WraN5omupcFDMgaU+uV0QBeNCMiUymjP1qGJm8hqsyu2RY3U7NLfn54F EPU1jFpn0N4gZTtVTx/nIKOAXdI18EK2uXZreDYXCSrOQyJF5d+B56KbZSnzD6Ehvr5o m0URnBw/09KygC5MXK2xT7sPrDqumhH8QDk+5C2Lm2oAMKDaXB/+EI143Kwg6Mx8kLKd Q8cS2seWxCRLB6A1nlTXL7CQPPlnCIseuq5qfa567lHNNrkY+JGfUlMWesk47sP0W8aW UV5xhgOdGEdtBvgYLCIR8xslQKpCnCGP5eAj/F0uBRw0mYYdlLWMBik+ZGMyxnYcwNi6 y/nw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=12pdMTxqi83EEHwmbAWeg9wmewWbN2jswxBvTfN4Tx4=; b=b2D286os57yruQ8Pq95YzEbYXSwVaXCQgwFcF9UE8fQZ69IzLbyiJDd01g+b03pGpc 5kQJvoHfUuyzwUJZpeR9ahxxAOgqETqEep3MMi4eCgq+LCly/4bEAoNi6z6DXAA5VAcJ S5Kg5zi+5OLuO5zc9xsur0FHn8xkVL6Z5r5Z3YIboTBEx7r2CUkkwafD0OFK8SUyPQwb RNAB1qR/KE+RaseIbewiRVHmAHwIHaT3Ou0vhO3hyIO+ONQLE+thvV+7S1h1U0bp0ygP FiIgUIgHosZU9tKuMeZV6fubJxAToKQFJG+zY1IFyySFiF9TNOWQBXTPlULL8UkiZ6js /52A== X-Gm-Message-State: AJcUukcew7vX+evtaX7Q51UwFF+Ufzy2+LjqeutBM5GXIWn2JS8SDp6s sSYPv3PNgMswBcaXPek+Zv0P2fmVksXrM8fodJ3njA== X-Google-Smtp-Source: ALg8bN5szFGR70yAx+7w804SW60dQFWqcQhHcibuHwNACfmb+lm5JCP7yrlLJmLn1hLRRPVPOxjan9YU5HRcmF/+5wc= X-Received: by 2002:a9d:6a50:: with SMTP id h16mr12556790otn.95.1547343817474; Sat, 12 Jan 2019 17:43:37 -0800 (PST) MIME-Version: 1.0 References: <20190109144736.17452-1-pagupta@redhat.com> <20190110012617.GA4205@dastard> <20190110101757.GC15790@quack2.suse.cz> <1354249849.63357171.1547343519970.JavaMail.zimbra@redhat.com> In-Reply-To: <1354249849.63357171.1547343519970.JavaMail.zimbra@redhat.com> From: Dan Williams Date: Sat, 12 Jan 2019 17:43:26 -0800 Message-ID: Subject: Re: [PATCH v3 0/5] kvm "virtio pmem" device To: Pankaj Gupta Cc: Jan Kara , Dave Chinner , Linux Kernel Mailing List , KVM list , Qemu Developers , linux-nvdimm , linux-fsdevel , virtualization@lists.linux-foundation.org, Linux ACPI , linux-ext4 , linux-xfs , Stefan Hajnoczi , Rik van Riel , Nitesh Narayan Lal , Kevin Wolf , Paolo Bonzini , Ross Zwisler , vishal l verma , dave jiang , David Hildenbrand , jmoyer , xiaoguangrong eric , Christoph Hellwig , "Michael S. Tsirkin" , Jason Wang , lcapitulino@redhat.com, Igor Mammedov , Eric Blake , Matthew Wilcox , "Theodore Ts'o" , adilger kernel , darrick wong , "Rafael J. Wysocki" Content-Type: text/plain; charset="UTF-8" Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Message-ID: <20190113014326.sKMLXBhz911O-HTZPgEQMM0W5CFokEhVvHrf5sTloW0@z> On Sat, Jan 12, 2019 at 5:38 PM Pankaj Gupta wrote: > > > > > > > On Thu 10-01-19 12:26:17, Dave Chinner wrote: > > > On Wed, Jan 09, 2019 at 08:17:31PM +0530, Pankaj Gupta wrote: > > > > This patch series has implementation for "virtio pmem". > > > > "virtio pmem" is fake persistent memory(nvdimm) in guest > > > > which allows to bypass the guest page cache. This also > > > > implements a VIRTIO based asynchronous flush mechanism. > > > > > > Hmmmm. Sharing the host page cache direct into the guest VM. Sounds > > > like a good idea, but..... > > > > > > 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). > > > > > > Which means this functionality looks to me like a new vector for > > > information leakage into and out of the guest VM via guest > > > controlled host page cache manipulation. > > > > > > https://arxiv.org/pdf/1901.01161 > > > > > > I might be wrong, but if I'm not we're going to have to be very > > > careful about how guest VMs can access and manipulate host side > > > resources like the page cache..... > > > > Right. Thinking about this I would be more concerned about the fact that > > guest can effectively pin amount of host's page cache upto size of the > > device/file passed to guest as PMEM, can't it Pankaj? Or is there some QEMU > > magic that avoids this? > > Yes, guest will pin these host page cache pages using 'get_user_pages' by > elevating the page reference count. But these pages can be reclaimed by host > at any time when there is memory pressure. Wait, how can the guest pin the host pages? I would expect this to happen only when using vfio and device assignment. Otherwise, no the host can't reclaim a pinned page, that's the whole point of a pin to prevent the mm from reclaiming ownership. > KVM does not permanently pin pages. vfio does that but we are not using > it here. Right, so I'm confused by your pin assertion above.