* Peng Tao (bergwolf@hyper.sh) wrote:
On Tue, Jun 4, 2019 at 5:53 PM Dr. David Alan Gilbert <dgilbert@redhat.com> wrote:
* Tao Peng (bergwolf@hyper.sh) wrote:
On Tue, Jun 4, 2019 at 7:18 AM Mahalingam, Ganesh <ganesh.mahalingam@intel.com> wrote:
Peng, Stefan, While working on enabling virtio-fs on Kata there was a small confusion on whether virtio-fs can work with VM Templating. With the current setup of kata, VM templating and virtio-fs are mutually exclusive (VM templating is enabled in qemu-lite and virtio-fs currently only with NEMU), but they will converge very soon.
An open question we had was, would they both work with each other given that VM templating turns off memory sharing for all VMs other than the first one and virtio-fs expects guest memory be shared & file-backed for all VMs.
Hi Stefan,
What happens if we specify share=on and share=off for different memory file backends? Can virtio-fs only pick up the shared one?
All vhost-user devices (including virtio-fs) need the share=on - because that's the only way that the vhost-user process sees the writes done by qemu or the guest. I think we need it for all of RAM.
Hmm, vm templating needs the initial ram to be mapped private so that it can be shared safely across multiple VM instances. It does conflict with vhost-user requirement that guest memory can be accessed by a different process.
Yes, it's hard. Thre's a really nasty idea I had last year, https://lists.gnu.org/archive/html/qemu-devel/2018-04/msg03055.html that *might* work for vhost-user + templating. You'd still need to hotplug the virtio-fs device after restoring from the template.
Ganesh, how about we just marking vm templating and vhost-user conflict with each other?
Slightly related, but we should see if we can use QEMU's x-ignore-shared-ram flag to do the templating in qemu 4.0; I think that should do the same as the older NEMU code. Dave
Cheers, Tao -- Into something rich and strange. -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK