Re: Should KVM_GUEST stop depending on PARAVIRT?

[Paolo Bonzini <pbonzini@redhat.com>]

On 24/07/2015 19:33, Andy Lutomirski wrote:
> PARAVIRT adds a fair amount of bloat and, AFAICT, KVM_GUEST doesn't
> really need any of it.  Would it make sense to drop the dependency?

I think the main reason for PARAVIRT is that pv kernels have by default

        .read_msr = native_read_msr_safe,
        .write_msr = native_write_msr_safe,

Unfortunately Intel adds a bunch of performance measurement features
saying that "they work with this cpuid family/model/stepping" and at the
same time attach them to some non-architectural MSRs that, in principle
could be reused for something else years down the road.  This is not a
huge problem for Windows, where only tools such as vTune use these MSRs,
but it is a problem for Linux.

The alternative is ignore_msrs, but that's a very big hammer too.

Paolo