On 2012-06-01 19:03, Alex Williamson wrote: > On Fri, 2012-06-01 at 18:39 +0200, Jan Kiszka wrote: >> On 2012-06-01 18:16, Alex Williamson wrote: >>> The kernel no longer allows us to pass NULL for a hard interrupt >>> handler without IRQF_ONESHOT. Should have been using this flag >>> anyway. >> >> This make the IRQ handling tail a bit slower (due to >> irq_finalize_oneshot). MSIs are edge-triggered, so there was no need for >> masking in theory. > > Aren't these asynchronous since we can theoretically do > irq_finalize_oneshot while the guest is servicing the device? If it runs on a different CPU. But usually it's more efficient to have handler and user on the same CPU. And this work has to be processed somewhere. > >> Hmm, can't we trust the information that an IRQ >> grabbed here is really a MSI type? > > > Apparently not, comment added with this check (1c6c6952): > > * The interrupt was requested with handler = NULL, so > * we use the default primary handler for it. But it > * does not have the oneshot flag set. In combination > * with level interrupts this is deadly, because the > * default primary handler just wakes the thread, then > * the irq lines is reenabled, but the device still > * has the level irq asserted. Rinse and repeat.... > * > * While this works for edge type interrupts, we play > * it safe and reject unconditionally because we can't > * say for sure which type this interrupt really > * has. The type flags are unreliable as the > * underlying chip implementation can override them. I was talking about KVM here: Can't the KVM device assignment code ensure that only MSIs are registered as such so that the above concerns no longer apply? Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
