Re: [PATCH v2 5/5] KVM: x86: hyper-v: Deactivate APICv only when AutoEOI feature is in use

[Paolo Bonzini]

On 25/05/21 08:23, Vitaly Kuznetsov wrote:
> > Should it also disable APICv unconditionally if
> > HV_DEPRECATING_AEOI_RECOMMENDED is not in the guest CPUID?  That should
> > avoid ping-pong between enabled and disabled APICv even in pathological
> > cases that we cannot think about.
> When you run Hyper-V on KVM it doesn't use SynIC (let alone AutoEOI) but
> we still inhibit APICv unconditionally. The patch as-is improves this
> without any userspace changes required and I see it as a benefit. Going
> forward, we will definitely add something like 'hv-synic-noaeoi' to QEMU
> to make non-nesting setups benefit too but it'll take a while for this
> option to propagate to real world configurations (sigh).

Ok, if enable<->disable APICv becomes an issue we can also consider 
disabling APICv forever if AutoEOI is ever used.

Paolo