Re: [PATCH 1/2] nVMX: Add KVM_REQ_IMMEDIATE_EXIT

[Marcelo Tosatti <mtosatti@redhat.com>]

On Sun, Sep 25, 2011 at 11:13:06AM +0300, Nadav Har'El wrote:
> On Fri, Sep 23, 2011, Marcelo Tosatti wrote about "Re: [PATCH 1/2] nVMX: Add KVM_REQ_IMMEDIATE_EXIT":
> > On Thu, Sep 22, 2011 at 01:52:56PM +0300, Nadav Har'El wrote:
> > > This patch adds a new vcpu->requests bit, KVM_REQ_IMMEDIATE_EXIT.
> > > This bit requests that when next entering the guest, we should run it only
> > > for as little as possible, and exit again.
> > > 
> > > We use this new option in nested VMX: When L1 launches L2, but L0 wishes L1
> >...
> > > @@ -5647,6 +5648,8 @@ static int vcpu_enter_guest(struct kvm_v
> > >  		}
> > >  		if (kvm_check_request(KVM_REQ_STEAL_UPDATE, vcpu))
> > >  			record_steal_time(vcpu);
> > > +		req_immediate_exit =
> > > +			kvm_check_request(KVM_REQ_IMMEDIATE_EXIT, vcpu);
> >...
> > The immediate exit information can be lost if entry decides to bail out.
> > You can do 
> > 
> >         req_immediate_exit = kvm_check_request(KVM_REQ_IMMEDIATE_EXIT)
> > after preempt_disable()
> > and then transfer back the bit in the bail out case in
> > if (vcpu->mode == EXITING_GUEST_MODE || vcpu->requests
> 
> Thanks.
> 
> But thinking about this a bit, it seems to me that in my case *losing* this
> bit on a canceled entry is the correct thing to do, as turning on this bit was
> decided in the injection phase (in enable_irq_window()), and next time, if
> the reason to turn on this bit still exists (i.e., L0 has something to inject
> to L1, but L2 needs to run), we will turn it on again.

Correct, the loss is irrelevant.