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? Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
