Re: [PATCH RFC 4/6] KVM: x86: acknowledgment mechanism for async pf page ready notifications

[Paolo Bonzini]

On 05/05/20 10:51, Gavin Shan wrote:
>> How does the guest know if host has any pending events or not?
> 
> One way would be through struct kvm_vcpu_pv_apf_data, which is visible
> to host and guest. In the host, the workers that have completed their
> work (GUP) are queued into vcpu->async_pf.done. So we need a bit in
> struct kvm_vcpu_pv_apf_data, written by host while read by guest to
> see if there pending work. I even don't think the writer/reader need
> to be synchronized.

No, this cannot work.  The problem is that you need a way to tell the
host "you can give me another ready page", and a memory location is not
enough for that.

Paolo