Re: [Xen-devel] [PATCH v9 11/17] vt-d: Add API to update IRTE when VT-d PI is used

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.11.15 at 08:56, <kevin.tian@xxxxxxxxx> wrote:
>>  From: Wu, Feng
>> Sent: Tuesday, November 24, 2015 3:54 PM
>> > From: Tian, Kevin
>> > Sent: Tuesday, November 24, 2015 3:45 PM
>> > > +    /* Setup/Update interrupt remapping table entry. */
>> > > +    setup_posted_irte(&new_ire, &old_ire, pi_desc, gvec);
>> > > +    ret = cmpxchg16b(p, &old_ire, &new_ire);
>> > > +
>> > > +    /*
>> > > +     * In the above, we use cmpxchg16 to atomically update the 128-bit
>> > IRTE,
>> > > +     * and the hardware cannot update the IRTE behind us, so the return
>> > value
>> >
>> > hardware can DEFINITELY update IRTE behind us, right? e.g. after the IRTE
>> > entry
>> > is fully up, when interrupt is posted, etc. Here you might mean hardware
>> > cannot
>> > update the IRTE at this point?
>> 
>> Yes, you description above is more accurate. But why hardware needs to
>> update IRTE when interrupt is posted? I think it needs to update the
>> posted interrupt descriptor when posting an interrupt, not the IRTE,
>> right?
> 
> sorry mess IRTE and posted descriptor together. but using "behind"
> is still not accurate to state your point here. :-)

Well, "behind us" and "behind our back" seem to mean mostly the
same to me.

Jan


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