Re: [RFC v2] KVM: x86/vmx: Suppress posted interrupt notification when CPU is in host

Chao Gao
2022-09-28T10:58:11Z

>> Changes in v2 (addressed comments from Kevin):
>> - measure/estimate the impact to non-IPC-intensive cases
>> - don't tie PID.SN to vcpu->mode. Instead, clear PID.SN
>> right before VM-entry and set it after VM-exit.
>
>One correction here. My comment in v1 [1] was actually close to Sean's
>suggestion, i.e. opposite to above description:

Hi Kevin,

Yes. The changelog is misleading. You suggested using a dedicate hook.
And I indeed agreed to follow the suggestion. But as you said, what v2
does is the complete opposite of the suggestion.

The reason is when I started v2 recently, the idea of clearing SN right
before VM-entry came to my mind. Since it could also solve some problems
of v1 without a hook (hence, more self-contained), I thought it was
slightly better. But I missed that clearing SN right before VM-entry can
cause unnecessary SN toggling to VM-exit fast-path.