Re: [PATCH] kvm: VMX: do not use vm-exit instruction length for fast MMIO

[Paolo Bonzini <pbonzini@redhat.com>]

On 18/08/2017 13:57, David Hildenbrand wrote:
> What about a hack:
> 
> 1. clear instruction length when entering
> 2. check if instruction length is set when trying to forward the RIP
> 2a. if set, use it
> 2b. if not set, compute it

It's undefined, so we don't know that the instruction length remains
zero (also, on older processors and possibly some nested setups the
field is read-only).

Testing the hypervisor bit is the first line of action.

Paolo

> this at least should give full speedup in existing setups. Not 99%
> architecturally correct but might just work.
>