Re: [PATCH] x86/kvm: refine condition for checking vCPU preempted

[Sean Christopherson <seanjc@google.com>]

On Thu, Mar 30, 2023, Li,Rongqing wrote:
> > From: Sean Christopherson <seanjc@google.com>
> > On Thu, Mar 16, 2023, Li,Rongqing wrote:
> > > > From: Sean Christopherson <seanjc@google.com> On Wed, Mar 15, 2023,
> > > > Li,Rongqing wrote:
> > > > > > Rather than have the guest rely on host KVM behavior clearing
> > > > > > PV_UNHALT when HLT is passed through), would it make sense to
> > > > > > add something like KVM_HINTS_HLT_PASSTHROUGH to more explicitly
> > > > > > tell the guest that HLT isn't intercepted?
> > > > >
> > > > > KVM_HINTS_HLT_PASSTHROUGH is more obvious, but it need both kvm
> > > > > and guest support
> > > >
> > > > Yeah, that's the downside.  But modifying KVM and/or the userspace
> > > > VMM shouldn't be difficult, i.e the only meaningful cost is the
> > > > rollout of a new kernel/VMM.
> > > >
> > > > On the other hand, establishing the heuristic that !PV_UNHALT ==
> > > > HLT_PASSTHROUGH could have to subtle issues in the future.  It
> > > > safe-ish in the context of this patch as userspace is unlikely to
> > > > set KVM_HINTS_REALTIME, hide PV_UNHALT, and _not_ passthrough HLT.
> > > > But without the REALTIME side of things, !PV_UNHALT ==
> > HLT_PASSTHROUGH is much less likely to hold true.
> > >
> > > Ok, could you submit these codes
> > 
> > I'd like to hear from others first, especially Paolo and/or Wanpeng.
> 
> I see no progress
> How about to adopt this patch at first, it can give small performance for existing KVM and setup
> Then you continue to modify the kernel/VMM to give better support for KVM/guest

Guest-side KVM stuff is not my maintenance domain, i.e. this needs Paolo's
attention no matter what.