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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.12.16 at 09:53, <kevin.tian@xxxxxxxxx> wrote:
>>  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.

Ah, okay. Thanks for explaining this to me.

Jan


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