Re: [Xen-devel] [PATCH 3/3] VMX: Remove the vcpu from the per-cpu blocking list after domain termination

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Wu, Feng
> Sent: Monday, May 23, 2016 1:48 PM
> > -----Original Message-----
> > From: Tian, Kevin
> > Sent: Monday, May 23, 2016 1:19 PM
> > To: Wu, Feng <feng.wu@xxxxxxxxx>; xen-devel@xxxxxxxxxxxxx
> > Cc: keir@xxxxxxx; jbeulich@xxxxxxxx; andrew.cooper3@xxxxxxxxxx;
> > george.dunlap@xxxxxxxxxxxxx; dario.faggioli@xxxxxxxxxx;
> > konrad.wilk@xxxxxxxxxx
> > Subject: RE: [PATCH 3/3] VMX: Remove the vcpu from the per-cpu blocking list
> > after domain termination
> >
> > > From: Wu, Feng
> > > Sent: Friday, May 20, 2016 4:54 PM
> > >
> > > We need to make sure the bocking vcpu is not in any per-cpu blocking list
> > > when the associated domain is going to be destroyed.
> > >
> > > Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
> > > ---
> > >  xen/arch/x86/hvm/vmx/vmx.c | 32
> > > ++++++++++++++++++++++++++++++++
> > >  1 file changed, 32 insertions(+)
> > >
> > > diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> > > index 4862b13..e74b3e7 100644
> > > --- a/xen/arch/x86/hvm/vmx/vmx.c
> > > +++ b/xen/arch/x86/hvm/vmx/vmx.c
> > > @@ -248,6 +248,36 @@ void vmx_pi_hooks_deassign(struct domain *d)
> > >      d->arch.hvm_domain.vmx.pi_switch_to = NULL;
> > >  }
> > >
> > > +static void vmx_pi_blocking_list_cleanup(struct domain *d)
> >
> > Is it more natural to move such cleanup under vcpu destroy?
> 
> Yes, indeed it is more natural to add this function when vcpu is destroyed,
> however, the reason I add it here is I still have some concerns about the 
> timing.
> When the VM is destroyed, here is the calling path:
> 
> - vmx_pi_hooks_deassign() -->
> ......
> - vmx_vcpu_destroy() -->
> ......
> - vmx_domain_destroy()
> ......
> 
> As I replied in the previous mail, when we remove the vcpus from the blocking
> list, there might be some _in-flight_ call to the hooks, so I put the cleanup
> code in the vmx_domain_destroy(), which is a bit more far from 
> vmx_pi_hooks_deassign,
> and hence safer. If you have any other good ideas, I am all ears!:)
> 

If we don't need reset callbacks at deassign path, as commented for patch 1/3,
would it make above puzzle away? :-)

Thanks
Kevin

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