Re: [PATCH 1/8] qmp: Support for querying stats

["Daniel P. Berrangé" <berrange@redhat.com>]

On Thu, May 05, 2022 at 09:10:17AM +0200, Paolo Bonzini wrote:
> 
> 
> Il 4 maggio 2022 15:22:27 CEST, Markus Armbruster <armbru@redhat.com> ha scritto:
> >Can you point to existing uses of KVM binary stats introspection data?
> 
> There's none, but Google is using it in house. The same data was
> available before in debugfs and available via the kvm_stat script,
> so you could also refer to Christian Borntraeger's KVM Forum 2019
> talk. The problems with debugfs are basically that it's only
> available to root and is disabled by secure boot (both issues
> are not fixable on general because they are Linux policy).

Libvirt currently uses debugfs to get

 /sys/kernel/debug/kvm/-/halt_poll_success_ns

when we report on CPU usage for VMs. WHen kernel lockdown is enforced
under secure boot we're unable to access this file and even worse
every attempt to access it spams dmesg[1].  We need this query stats
QMP support for that single statistic alone today.


With regards,
Daniel

[1] https://gitlab.com/libvirt/libvirt/-/issues/213
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