Re: [Xen-devel] [PATCH v7 15/17] vmx: VT-d posted-interrupt core logic handling

["Wu, Feng" <feng.wu@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Tuesday, September 22, 2015 5:00 PM
> To: Wu, Feng
> Cc: Andrew Cooper; Dario Faggioli; George Dunlap; George Dunlap; Tian, Kevin;
> xen-devel@xxxxxxxxxxxxx; Keir Fraser
> Subject: RE: [Xen-devel] [PATCH v7 15/17] vmx: VT-d posted-interrupt core 
> logic
> handling
> 
> >>> On 22.09.15 at 09:19, <feng.wu@xxxxxxxxx> wrote:
> > However, I do find some issues with my proposal above, see below:
> >
> > 1. Set _VPF_blocked
> > 2. ret = arch_block()
> > 3. if ( ret || local_events_need_delivery() )
> >     clear_bit(_VPF_blocked, &v->pause_flags);
> >
> > After step #2, if ret == false, that means, we successfully changed the PI
> > descriptor in arch_block(), if local_events_need_delivery() returns true,
> > _VPF_blocked is cleared. After that, external interrupt come in, hence
> > pi_wakeup_interrupt() --> vcpu_unblock(), but _VPF_blocked is cleared,
> > so vcpu_unblock() does nothing, so the vCPU's PI state is incorrect.
> >
> > One possible solution for it is:
> > - Disable the interrupts before the check in step #3 above
> > - if local_events_need_delivery() returns true, undo all the operations
> >  done in arch_block()
> > - Enable interrupts after _VPF_blocked gets cleared.
> 
> Couldn't this be taken care of by, if necessary, adjusting PI state
> in vmx_do_resume()?

What do you mean here? Could you please elaborate? Thanks!

Thanks,
Feng

> 
> Jan


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