On Tue, Jan 24, 2017 at 04:00:55PM +0100, Paolo Bonzini wrote: > > > On 24/01/2017 15:44, Michael S. Tsirkin wrote: > > On Tue, Jan 24, 2017 at 10:25:00AM +0100, Paolo Bonzini wrote: > >> > >> > >> On 23/01/2017 18:04, Michael S. Tsirkin wrote: > >>>> For virtio-blk, my patch moved the setting of ISR from > >>>> virtio_queue_guest_notifier_read to virtio_notify_irqfd. This is > >>>> because the irqfd emulation only needs to trigger the interrupt. > >>>> Setting the ISR should have been done elsewhere. > >>>> > >>>> Can vhost set ISR (I thought it couldn't)? If so, it seems like ARM was > >>>> relying on QEMU's irqfd emulation, as a work around for vhost not > >>>> setting ISR. But this only works if irqfd is directed to QEMU and not > >>>> to KVM. So if vhost cannot set ISR, I think vhost should be disabled > >>>> unless MSI is active. > >>>> > >>>> Am I missing something? > >>> > >>> vhost doesn't set ISR ATM. Without MSI we are always bouncing > >>> interrupts through QEMU in particular in order to set ISR. > >> > >> Where is the code that disables KVM irqfd? > > > > This bit in virtio_pci_set_guest_notifiers does the trick I think: > > > > > > bool with_irqfd = msix_enabled(&proxy->pci_dev) && > > kvm_msi_via_irqfd_enabled(); > > > > I don't think we ever used irqfd for level interrupts. > > Ok, thanks! > > So we have four cases: > > - assign with emulated irqfd + ISR > - assign with emulated irqfd > - assign with irqfd > - deassign > > Currently we don't distinguish the first two, so (which I don't like) > Shannon's patch ends up setting ISR twice.
I don't see this yet - where is it set twice? > The only (ugly) solution > that comes to mind is making with_irqfd an enum... > > Paolo