On Wed, Jun 27, 2012 at 02:38:43PM +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. > That's not how ioapic/pic edge interrupts work. > 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? > > > > > But at least they actually worked reliably. Hmm. One way to address > > > this is to add kvm_trigger_irq which will trigger edge interrupts > > > unconditionally. > > > > > > Not sure it's worth it though. > > > > > > > > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > > > > > --- > > > > > virt/kvm/eventfd.c | 1 - > > > > > 1 file changed, 1 deletion(-) > > > > > > > > > > diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c > > > > > index f59c1e8..4db6b01 100644 > > > > > --- a/virt/kvm/eventfd.c > > > > > +++ b/virt/kvm/eventfd.c > > > > > @@ -68,7 +68,6 @@ irqfd_inject(struct work_struct *work) > > > > > struct kvm *kvm = irqfd->kvm; > > > > > > > > > > kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 1); > > > > > - kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0); > > > > > } > > > > > > > > > > /* > > > > > -- > > > > > MST > > > > > > > > -- > > > > Gleb. > > > > -- > > Gleb. -- Gleb. -- 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
