On 08/11/17 09:13, Auger Eric wrote: > Hi Marc, > > On 27/10/2017 16:28, Marc Zyngier wrote: >> Yet another braindump so I can free some cells... >> >> Acked-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx> >> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx> >> --- >> virt/kvm/arm/vgic/vgic-v4.c | 67 +++++++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 67 insertions(+) >> >> diff --git a/virt/kvm/arm/vgic/vgic-v4.c b/virt/kvm/arm/vgic/vgic-v4.c >> index d10e18eabd3b..e367d65a0ebe 100644 >> --- a/virt/kvm/arm/vgic/vgic-v4.c >> +++ b/virt/kvm/arm/vgic/vgic-v4.c >> @@ -23,6 +23,73 @@ >> >> #include "vgic.h" >> >> +/* >> + * How KVM uses GICv4 (insert rude comments here): >> + * >> + * The vgic-v4 layer acts as a bridge between several entities: >> + * - The GICv4 ITS representation offered by the ITS driver >> + * - VFIO, which is in charge of the PCI endpoint >> + * - The virtual ITS, which is the only thing the guest sees >> + * >> + * The configuration of VLPIs is triggered by a callback from VFIO, >> + * instructing KVM that a PCI device has been configured to deliver >> + * MSIs to a vITS. > We actually have a negotiation protocol between VFIO PCI (irq bypass > producer) and KVM irqfd (IRQ bypass consumer). When both recognize they > are tied together, handling an MSI tunneling, they initiate the > forwarding setup. >> + * >> + * kvm_vgic_v4_set_forwarding() is thus called with the routing entry, >> + * and this is used to find the corresponding vITS data structures >> + * (ITS instance, device, event and irq) using a process that is >> + * extremely similar to the injection of an MSI. > > Is it correct to say we replace the following injection chain: > > pEventID| > (pITS) |-> pLPIID -> VFIO PCI IRQ handler -> KVM irqfd ... > pDevID | > > vEventID| > ... inject (vITS) | -> vLPIID > vDevID | > > by > > pEventID| > (pITS) | -> vLPIID > pDevID | That's indeed a pretty accurate description of what happens, with a side messaging (doorbells). Thanks, M. -- Jazz is not dead. It just smells funny...
