On Wed, Jun 27, 2012 at 08:41:57AM -0600, Alex Williamson wrote: > On Wed, 2012-06-27 at 14:38 +0300, Michael S. Tsirkin wrote: > > On Wed, Jun 27, 2012 at 01:22:54PM +0300, Gleb Natapov wrote: > > > On Wed, Jun 27, 2012 at 01:20:24PM +0300, Michael S. Tsirkin wrote: > > > > On Wed, Jun 27, 2012 at 01:03:46PM +0300, Gleb Natapov wrote: > > > > > On Wed, Jun 27, 2012 at 12:13:43PM +0300, Michael S. Tsirkin wrote: > > > > > > irqfd sets and clears the level immediately. > > > > > > This used to be necessary for MSI interrupts but isn't anymore. > > > > > > > > > > > > Note! We never officially supported irqfd for level > > > > > > interrupts but it usually seemed to kind of work, > > > > > > and this change will break it. There are no known > > > > > > real users of that feature though - only old vfio prototypes. > > > > > > Removing this line will make it easier to add > > > > > > real support for level irqfds in the future. > > > > > > > > > > > Did we officially supported irqfd for ioapic/pic edge interrupts? > > > > > Because those will break to. > > > > > > > > Hard to say - as Alex points out it was never documented. > > > If we will start dropping everything that was never documented we will > > > hardly have working VMM at the end :) > > > > Generally true. > > > > However I just realized that this interface does not work > > reliably for ioapic/pic edge either. More or less for the same reason that > > it does not work for edge: we set bit in IRR, try to inject, > > then clear even if injection failed (e.g. because it is low > > priority). Guest will never get an interrupt in this case. > > > > So what happened e.g. for Alex's vfio prototype is he never > > hit an interrupt window in light testing. > > > > What we would need to do to fix it is: > > > > > > - kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 1); > > > > > > - kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0); > > > > > > + kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0); > > > > > > + kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 1); > > > > Which will fix edge but break level same as this patch. > > But is it worth fixing? Maybe declare it broken and be > > done with it? > > Ugh, so if I understand correctly, the case where kvm_set_irq() returns > <0, we're broken. Gleb says it's not broken. Maybe I misread the code. Need more investigation. > VFIO has masked the physical device and has no error > path to know that the interrupt inject was unsuccessful. We almost need > an error eventfd that bounces the interrupt back to userspace for the > qemu interrupt model to handle, but that has it's own set of > complications. Suggestions? Declaring the interface broken isn't very > useful. Thanks, > > Alex -- 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
