On Thu, Mar 08, 2018 at 05:28:44PM +0000, Marc Zyngier wrote: > On Thu, 08 Mar 2018 16:19:00 +0000, > Christoffer Dall wrote: > > > > On Thu, Mar 08, 2018 at 11:54:27AM +0000, Marc Zyngier wrote: > > > On 08/03/18 09:49, Marc Zyngier wrote: [...] > > > The state is now pending, we've really EOI'd the interrupt, and > > > yet lr_signals_eoi_mi() returns false, since the state is not 0. > > > The result is that we won't signal anything on the corresponding > > > irqfd, which people complain about. Meh. > > > > So the core of the problem is that when we've entered the guest with > > PENDING+ACTIVE and when we exit (for some reason) we don't signal the > > resamplefd, right? The solution seems to me that we don't ever do > > PENDING+ACTIVE if you need to resample after each deactivate. What > > would be the point of appending a pending state that you only know to be > > valid after a resample anyway? > > The question is then to identify that a given source needs to be > signalled back to VFIO. Calling into the eventfd code on the hot path > is pretty horrid (I'm not sure if we can really call into this with > interrupts disabled, for example). > This feels like a bad layering violation to me as well. > > > > > > > > Example 2: > > > P+A -> guest EOI -> P -> delayed MI -> guest IAR -> A -> MI fires > > > > We could be more clever and do the following calculation on every exit: > > > > If you enter with P, and exit with either A or 0, then signal. > > > > If you enter with P+A, and you exit with either P, A, or 0, then signal. > > > > Wouldn't that also solve it? (Although I have a feeling you'd miss some > > exits in this case). > > I'd be more confident if we did forbid P+A for such interrupts > altogether, as they really feel like another kind of HW interrupt. How about a slightly bigger hammer: Can we avoid doing P+A for level interrupts completely? I don't think that really makes much sense, and I think we simply everything if we just come back out and resample the line. For an edge, something like a network card, there's a potential performance win to appending a new pending state, but I doubt that this is the case for level interrupts. The timer would be unaffected, because it's a HW interrupt. Thanks, -Christoffer _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
