On Thu, May 05, 2016 at 05:27:03PM +0200, Ladi Prosek wrote: > On Thu, May 5, 2016 at 5:20 PM, Michael S. Tsirkin <m...@redhat.com> wrote: > > On Thu, May 05, 2016 at 05:15:01PM +0200, Ladi Prosek wrote: > >> On Thu, May 5, 2016 at 5:02 PM, Michael S. Tsirkin <m...@redhat.com> wrote: > >> > On Thu, May 05, 2016 at 04:59:13PM +0200, Ladi Prosek wrote: > >> >> On Thu, May 5, 2016 at 3:36 PM, Michael S. Tsirkin <m...@redhat.com> > >> >> wrote: > >> >> > On Thu, May 05, 2016 at 11:13:37AM +0200, Ladi Prosek wrote: > >> >> >> There is a discrepancy between dataplane and no-dataplane virtio > >> >> >> behavior with respect to the ISR status register and MSI-X > >> >> >> capability. > >> >> >> > >> >> >> Without dataplane the Queue interrupt ISR status bit is set > >> >> >> regardless of how the notification is delivered to the guest. > >> >> >> > >> >> >> With dataplane the Queue interrupt ISR status bit is set only > >> >> >> if the notification is delivered as an IRQ. > >> >> >> > >> >> >> While both conform to the spec, QEMU should be consistent to > >> >> >> minimize surprises with broken drivers. > >> >> >> > >> >> >> This RFC patch shows the relevant code location and contains a > >> >> >> possible fix which makes QEMU set the bit on the MSI dataplane > >> >> >> code path. > >> >> >> > >> >> >> Signed-off-by: Ladi Prosek <lpro...@redhat.com> > >> >> > > >> >> > How is this supposed to work when injecting interrupts using irqfd? > >> >> > If anything, I would rather drop setting the flag on non-dataplane. > >> >> > >> >> My bad, this is messed up. For some reason it works, or appears to be > >> >> working at least. > >> >> > >> >> The reason why I'd like to add setting the flag in dataplane is that > >> >> if we go the other way we'll break drivers. I know for sure that there > >> >> are drivers depending on this. > >> > > >> > Rly? These are way out of spec then. I'd rather have these drivers > >> > fixed: virtio said ISR can't be used with MSI since the 1st version > >> > where MSI was introduced. virtio 1.0 allows using ISR for config > >> > interrupts only. > >> > >> Should the below paragraph be worded differently then? Or explicitly > >> say that the contents of the status word is undefined? > > > > It says don't access. How would you word a driver requirement otherwise? > > I would use a stronger mode than "SHOULD NOT". Playing devil's > advocate, I could interpret the sentence as a suggested perf > optimization - i.e. the interrupt message conveys the required > information, no need to consult ISR status.
OK, maybe it should be "MUST NOT". Older virtio said it is not valid. Want to reports this on virtio comments mailing list? > >> Specified since > >> 1st version vs. actually behaving since 1st version. > > > > Yea. Yack. People just try whatever seems to work. > > > >> If you think it's > >> safe to remove the |= 0x01 from the regular path I'll fix the drivers > >> I know of, that's not a problem. > > > > Maybe we should keep the |= 0x01 in QEMU for now, but let's > > not mess up dataplace. Please fix the drivers. > > > > Maybe remove |= 0x01 if legacy is disabled. > > Ok, sounds good. Thanks! > > >> 4.1.4.5.2 Driver Requirements: ISR status capability > >> > >> If MSI-X capability is enabled, the driver SHOULD NOT access ISR > >> status upon detecting a Queue Interrupt. > >> > >> >> > > >> >> >> --- > >> >> >> hw/virtio/virtio.c | 19 ++++++++++++++----- > >> >> >> 1 file changed, 14 insertions(+), 5 deletions(-) > >> >> >> > >> >> >> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c > >> >> >> index 08275a9..4053313 100644 > >> >> >> --- a/hw/virtio/virtio.c > >> >> >> +++ b/hw/virtio/virtio.c > >> >> >> @@ -1192,7 +1192,7 @@ void virtio_notify(VirtIODevice *vdev, > >> >> >> VirtQueue *vq) > >> >> >> } > >> >> >> > >> >> >> trace_virtio_notify(vdev, vq); > >> >> >> - vdev->isr |= 0x01; > >> >> >> + vdev->isr |= 0x01; // <= here we set ISR status even if we > >> >> >> don't raise IRQ > >> >> >> virtio_notify_vector(vdev, vq->vector); > >> >> >> } > >> >> >> > >> >> >> @@ -1757,16 +1757,25 @@ static void > >> >> >> virtio_queue_guest_notifier_read(EventNotifier *n) > >> >> >> } > >> >> >> } > >> >> >> > >> >> >> +static void virtio_queue_guest_notifier_read_irqfd(EventNotifier *n) > >> >> >> +{ > >> >> >> + VirtQueue *vq = container_of(n, VirtQueue, guest_notifier); > >> >> >> + if (event_notifier_test_and_clear(n)) { > >> >> >> + vq->vdev->isr |= 0x01; > >> >> >> + } > >> >> >> +} > >> >> >> + > >> >> >> void virtio_queue_set_guest_notifier_fd_handler(VirtQueue *vq, bool > >> >> >> assign, > >> >> >> bool with_irqfd) > >> >> >> { > >> >> >> - if (assign && !with_irqfd) { > >> >> >> + if (assign) { > >> >> >> event_notifier_set_handler(&vq->guest_notifier, > >> >> >> - > >> >> >> virtio_queue_guest_notifier_read); > >> >> >> + with_irqfd ? > >> >> >> + virtio_queue_guest_notifier_read_irqfd : > >> >> >> + virtio_queue_guest_notifier_read); > >> >> >> } else { > >> >> >> event_notifier_set_handler(&vq->guest_notifier, NULL); > >> >> >> - } > >> >> >> - if (!assign) { > >> >> >> + > >> >> >> /* Test and clear notifier before closing it, > >> >> >> * in case poll callback didn't have time to run. */ > >> >> >> virtio_queue_guest_notifier_read(&vq->guest_notifier); > >> >> >> -- > >> >> >> 2.5.5