Comment 0 for bug 1776189

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Christian Ehrhardt  (paelzer) wrote :

Hi,
on the discussions and tests around bug 1769053 it was identified to long term it would be nice to expose host-pyhs-bits and phys-bits through libvirt.

That is what bug 1769053 and the related upstream BZ will continue to track.

But there are two shortcomings on this for now:
1. it takes way too long to get that done for people wanting to use this right now
2. even if it would be implemented in libvirt, the stacks above do not yet exploit the theoretical pyhs-bits related attributes.

To get Ubuntu Users with huge systems a rather quick access to this feature including usability in higher parts of the virtualization stack we want to somewhat follow what RedHat/CentOs do at [1]

There they just switch the default to "on" in the default machine type.
This has some potential drawbacks if you want to migrate across different generations of machines, therefore we don't want it to be the default in Ubuntu.

Instead we would prefer to add a type with a -large suffix could carry that.
Note: Bikeshedding on the name is appreciated until the change is done, then it is as it is.

I have tested code that does so and it makes maintaining Ubuntu machine types not much harder while at the same time providing our users mentioned benefits for huge guests.

Eventually this will lower the pain for those running this huge guests, and by that increase the time until someone does the exposure through libvirt and all the upper stack exploitation. But that is acceptable as price to get this fast and more easy at least to Cosmic and Bionic releases without breaking too much and the mentioned instant exploitation by components higher in the virt stack.

[1]: http://mirrors.ibiblio.org/ovirt/pub/ovirt-4.0/src/qemu-kvm-ev/kvm-target-i386-Enable-host-phys-bits-on-RHEL.patch