Re: [PATCH 3/3] i386: Make sure kvm_arch_set_tsc_khz() succeeds on migration when 'hv-reenlightenment' was exposed

[Paolo Bonzini]

On 18/03/21 17:38, Vitaly Kuznetsov wrote:
> > Could we instead fail to load the reenlightenment section if
> > user_tsc_khz was not set?  This seems to be user (well, management)
> > error really, since reenlightenment has to be enabled manually (or with
> > hv-passthrough which blocks migration too).
>
> Yes, we certainly could do that but what's the added value of
> user_tsc_khz which upper layer will have to set explicitly (probably to
> the tsc frequency of the source host anyway)? In case we just want to
> avoid calling KVM_SET_TSC_KHZ twice, we can probably achieve that by
> adding a CPU flag or something.

What I want to achieve is to forbid migration of VMs with 
reenlightenment, if they don't also specify tsc-khz to the frequency of 
the TSC on the source host.  We can't check it at the beginning of 
migration, but at least we can check it at the end.

Maybe we're talking about two different things?

Paolo