Re: [libvirt] [PATCH v2] qemu: Add check for whether KVM nesting is enabled
On Tue, 2018-11-27 at 14:15 -0500, John Ferlan wrote:
On 11/27/18 12:05 PM, Andrea Bolognani wrote:
> Oh, wait, I get it now: 'modprobe -c' doesn't dump the *current* host
> configuration, but the *static* one! So if you enable nested KVM
> support by doing
>
> # modprobe -r kvm_intel
> # modprobe kvm_intel nested=1
>
> like I did, then the check above will not report it as enabled even
> though it is; conversely, if you drop the appropriate config snippet
> in /etc/modprobe.d/ but don't reload the module it will report it as
> enabled even though it's not!
Ugh, sigh... Yep, I was thinking primarily the static config option
since we had helpers to read. Of course that won't be enough. Joy, more
code to probe... Maybe it is easier to just say - clear your
capabilities cache if you alter that particular kernel value.
You should be able to just read the contents of
/sys/module/kvm_{amd,intel}/parameters/nested
for x86_64; not sure whether a similar trick will work on s390, but
it will definitely *not* work on ppc64, and I haven't even started
thinking about aarch64 yet!
Of course there's the usual caveats about whether this has been
available in the kernel for a long enough time that it's okay for us
to rely on it, and whether the approach is not entirely flawed for
reasons that I'm not aware of :)
--
Andrea Bolognani / Red Hat / Virtualization