From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pankaj Gupta Subject: Re: [PATCH v3 0/5] kvm "virtio pmem" device Date: Mon, 14 Jan 2019 02:15:40 -0500 (EST) Message-ID: <942065073.64011540.1547450140670.JavaMail.zimbra@redhat.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190113233820.GX6310-PfSpb0PWhxZc2C7mugBRk2EX/6BAtgUQ@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" To: Matthew Wilcox Cc: jack-AlSwsSmVLrQ@public.gmane.org, kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, david-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, linux-nvdimm-y27Ovi1pjclAfugRpC6u6w@public.gmane.org, jasowang-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, Dave Chinner , qemu-devel-qX2TKyscuCcdnm+yROfE0A@public.gmane.org, virtualization-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, adilger kernel , zwisler-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, eblake-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, darrick wong , mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, linux-acpi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, riel-ebMLmSuQjDVBDgjK7y7TUQ@public.gmane.org, stefanha-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, imammedo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, lcapitulino-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, kwolf-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, nilal-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, tytso-3s7WtUTddSA@public.gmane.org, xiaoguangrong eric , rjw-LthD3rsA81gm4RdzfppkhA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-xfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, pbonzini-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org List-Id: linux-acpi@vger.kernel.org > > 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