Re: [Xen-devel] [PATCH v3] x86/apicv: fix RTC periodic timer and apicv issue

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

> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Tuesday, December 20, 2016 4:35 PM
> 
> >>> On 20.12.16 at 06:37, <kevin.tian@xxxxxxxxx> wrote:
> >>  From: Xuquan (Quan Xu) [mailto:xuquan8@xxxxxxxxxx]
> >> Sent: Friday, December 16, 2016 5:40 PM
> >> -        if (pt_vector != -1)
> >> -            vmx_set_eoi_exit_bitmap(v, pt_vector);
> >> +        if ( pt_vector != -1 ) {
> >> +            if ( intack.vector > pt_vector )
> >> +                vmx_set_eoi_exit_bitmap(v, intack.vector);
> >> +            else
> >> +                vmx_set_eoi_exit_bitmap(v, pt_vector);
> >> +        }
> >
> > Above can be simplified as one line change:
> >     if ( pt_vector != -1 )
> >             vmx_set_eoi_exit_bitmap(v, intack.vector);
> 
> Hmm, I don't understand. Did you mean to use max() here? Or
> else how is this an equivalent of the originally proposed code?
> 

Original code is not 100% correct. The purpose is to set EOI exit
bitmap for any vector which may block injection of pt_vector - 
give chance to recognize pt_vector in future intack and then do pt 
intr post. The simplified code achieves this effect same as original
code if intack.vector >= vector. I cannot come up a case why
intack.vector might be smaller than vector. If this case happens,
we still need enable exit bitmap for intack.vector instead of
pt_vector for said purpose while original code did it wrong.

Thanks
Kevin

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