On Sun, Jun 24, 2012 at 08:47:57AM -0600, Alex Williamson wrote: > On Sun, 2012-06-24 at 11:24 +0300, Michael S. Tsirkin wrote: > > On Fri, Jun 22, 2012 at 04:16:53PM -0600, Alex Williamson wrote: > > > I think we're probably also going to need something like this. > > > When running in non-accelerated qemu, we're going to have to > > > create some kind of EOI notifier for drivers. VFIO can make > > > additional improvements when running on KVM so it will probably > > > make use of the KVM_IRQFD_LEVEL_EOI interface, but we don't > > > want to have a generic EOI notifier in qemu that just stops > > > working when kvm-ioapic is enabled. This is just a simple way > > > to register an eventfd using the existing KVM ack notifier. > > > I tried combining the ack notifier of the LEVEL_EOI interface > > > into this one, but it didn't work out well. The code complexity > > > goes up a lot. > > > > > > Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx> > > > --- > > > > > > Documentation/virtual/kvm/api.txt | 14 ++++++ > > > arch/x86/kvm/x86.c | 1 > > > include/linux/kvm.h | 12 +++++ > > > include/linux/kvm_host.h | 7 +++ > > > virt/kvm/eventfd.c | 89 +++++++++++++++++++++++++++++++++++++ > > > virt/kvm/kvm_main.c | 9 ++++ > > > 6 files changed, 132 insertions(+) > > > > > > diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt > > > index 2f8a0aa..69b1747 100644 > > > --- a/Documentation/virtual/kvm/api.txt > > > +++ b/Documentation/virtual/kvm/api.txt > > > @@ -1998,6 +1998,20 @@ matched using kvm_irqfd.fd, kvm_irqfd.gsi, and kvm_irqfd.fd2. > > > De-assigning automatically de-asserts the interrupt line setup through > > > this interface. > > > > > > +4.77 KVM_EOI_EVENTFD > > > + > > > +Capability: KVM_CAP_EOI_EVENTFD > > > +Architectures: x86 > > > +Type: vm ioctl > > > +Parameters: struct kvm_eoi_eventfd (in) > > > +Returns: 0 on success, -1 on error > > > + > > > +This interface allows userspace to be notified through an eventfd for > > > +EOI writes to the in-kernel irqchip. kvm_eoi_eventfd.fd specifies > > > +the eventfd to signal on EOI to kvm_eoi_eventfd.gsi. To disable, > > > +use KVM_EOI_EVENTFD_FLAG_DEASSIGN and specify both the original fd > > > +and gsi. > > > + > > > 5. The kvm_run structure > > > ------------------------ > > > > > > > The patch looks like it only works for ioapic IRQs. I think it's a good > > idea to explicitly limit this to level interrupts, straight away: > > there's no reason for userspace to need an exit on an edge interrupt. > > Are you suggesting documentation or code to prevent users from binding > to an edge interrupt? Yes. > > I also suggest we put LEVEL somewhere in the name. > > Ok > > > With this eventfd, do we also need the fd2 parameter in the irqfd > > structure? It seems to be used for the same thing ... > > Yes we still need fd2, this does not replace KVM_IRQFD_LEVEL_EOI. The > models we need to support are: > > 1) assert from userspace (IRQ_LINE), eoi to userspace (EOI_EVENTFD), > de-assert from userspace (IRQ_LINE) > > 2a) assert from vfio (IRQFD.fd), de-assert in kvm, notify vfio > (IRQFD.fd2) > or > > 2b) assert from vfio (IRQFD.fd), eoi to vfio (EOI_EVENTFD), de-assert > from vfio (IRQFD.fd2) Or maybe deassert in kvm, notify vfio using eventfd? > > This series enables 1) and 2a). 2b) has some pros and cons. The pro is > that vfio could test the device to see if an interrupt is pending and > not de-assert if there is still an interrupt pending. The con is that a > standard level interrupt cycle takes 3 transactions instead of 2. > > Any case of triggering the interrupt externally via an irqfd requires > that the irqfd uses it's own irq_source_id so that it doesn't interfere > with KVM_USERSPACE_IRQ_SOURCE_ID. So we can't mix IRQ_LINE and IRQFD > unless we want to completely expose a new irq source id allocation > mechanism and include it in all the interfaces (KVM_GET_IRQ_SOURCE_ID, > KVM_PUT_IRQ_SOURCE_ID, pass a source id to IRQFD and IRQ_LINE, etc). > Thanks, > > Alex I don't follow this last paragraph. What are you trying to say? To support IRQ sharing for level irqs, each irqfd for level IRQ must have a distinct source id. But IRQ_LINE works fine without, and one source ID for all irq_line users seems enough. -- MST -- 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
