On Mon, Jun 23, 2014 at 06:47:51PM +0200, Alexander Graf wrote: > > On 17.06.14 13:39, Eric Auger wrote: > >Hello, > > > >I have a question related to KVM_IRQFD and KVM_SET_GSI_ROUTING ioctl > >relationship. > > > >When reading the KVM API documentation I do not understand there is any > >dependency between KVM_IRQFD and KVM_SET_GSI_ROUTING. According to the > >text it seems only the gsi field is used and interpreted as the irqchip pin. > > > >However irqchip.c kvm_set_irq code relies on an existing and not dummy > >routing table. > > > >My question is: does anyone agree on the fact the user-side must set a > >consistent routing table using KVM_SET_GSI_ROUTING before using > >KVM_IRQFD? The other alternative would have been to build a default > >identity GSI routing table in the kernel (gsi = irqchip.pin). > > I untangled irqfd support from the x86 ioapic emulation a while back. When I > looked at it, I didn't see any easy way to split it out from the routing > too, so I kept that dependency in. > > If you look at the code, you will see that the irq routing entry is used as > token for an irqfd. So every irqfd only knows its routing table entry, > nothing else. As far as I can see, the routing table entry is used for only two things: to tell whether the interrupt is an MSI or LSI, and to pass to kvm_set_msi. One way to tackle the problem would be to abstract out the routing table lookup into a function in irqchip.c, rather than having it open-coded in irqfd_update. Then, if you don't want to have the routing table you write an alternative function that creates a routing entry from scratch. It would need information from the low-level irq chip code as to which interrupts are LSIs and which are MSIs. It also ties you down to having only one kind of interrupt controller. The other way I see to solve my particular problem, which is that userspace tends to use hardware interrupt numbers starting at 4096, is to replace the arrays in struct kvm_irq_routing_table with idr structures or something similar. > Splitting that dependency out is certainly quite tedious work. However, I'm > sure the IBM folks will be grateful if you do it :). Indeed. :) Paul. -- 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
