> -----Original Message----- > From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx] > Sent: Thursday, June 25, 2015 3:49 AM > To: Eric Auger > Cc: Joerg Roedel; Avi Kivity; Wu, Feng; kvm@xxxxxxxxxxxxxxx; > linux-kernel@xxxxxxxxxxxxxxx; pbonzini@xxxxxxxxxx; mtosatti@xxxxxxxxxx > Subject: Re: [v4 08/16] KVM: kvm-vfio: User API for IRQ forwarding > > On Wed, 2015-06-24 at 18:25 +0200, Eric Auger wrote: > > Hi Joerg, > > > > On 06/24/2015 05:50 PM, Joerg Roedel wrote: > > > On Mon, Jun 15, 2015 at 06:17:03PM +0200, Eric Auger wrote: > > >> I guess this discussion also is relevant wrt "[RFC v6 00/16] KVM-VFIO > > >> IRQ forward control" series? Or is that "central registry maintained by > > >> a posted interrupts manager" something more specific to x86? > > > > > > From what I understood so far, the feature you implemented for ARM is a > > > bit different from the ones that get introduced to x86. > > > > > > Can you please share some details on how the ARM version works? I am > > > interested in how the GICv2 is configured for IRQ forwarding. The > > > question is whether the forwarding information needs to be updated from > > > KVM and what information about the IRQ KVM needs for this. > > > > The principle is that when you inject a virtual IRQ to a guest, you > > program a register in the GIC, known as a list register. There you put > > both the virtual IRQ you want to inject but also the physical IRQ it is > > linked with (HWbit mode set = forwarding set). When the guest completes > > the virtual IRQ the GIC HW automatically deactivates the physical IRQ > > found in the list register. In that mode the physical IRQ deactivation > > is under the ownership of the guest (actually automatically done by the HW). > > > > If HWbit mode is *not* set (forwarding not set), you do not specify the > > HW IRQ in the list register. The host deactivates the physical IRQ & > > masks it before triggering the virtual IRQ. Only the virtual IRQ ID is > > programmed in the list register. When the guest completes the virtual > > IRQ, a physical maintenance IRQ is triggered. The hyp mode is entered > > and eventually the host unmasks the IRQ. > > > > Some illustrations can be found in > > http://www.linux-kvm.org/images/a/a8/01x04-ARMdevice.pdf > > > I think an important aspect for our design is that in the case of Posted > Interrupts, they're only used for edge triggered interrupts so VFIO is > only an information provider for KVM to configure it. Exactly! For PI, KVM only needs some information from VFIO when the guests set the irq affinity. Thanks, Feng VFIO will > hopefully just see fewer interrupts as they magically appear directly in > the guest. IRQ Forwarding however affects the de-assertion of level > triggered interrupts. VFIO needs to switch to something more like an > edge handler when IRQ Forwarding is enabled. So in that model, VFIO > needs to provide information as well as consume it to change behavior. > Thanks, > > Alex ��.n��������+%������w��{.n�����o�^n�r������&��z�ޗ�zf���h���~����������_��+v���)ߣ�
