[PATCH v3 00/10] ARM IRQ forward control based on IRQ bypass manager

From: Eric Auger
Date: Mon Aug 10 2015 - 09:25:14 EST

This series allows to set ARM IRQ forwarding between a VFIO platform
device physical IRQ and a guest virtual IRQ. The link is coordinated
by the IRQ bypass manager.

The principle is the VFIO platform driver registers an IRQ bypass producer
struct on VFIO_IRQ_SET_ACTION_TRIGGER while KVM irqfd registers a consumer
struct on the irqfd assignment. This leads to a handshake based on the
eventfd context (used as token) match. When either of the producer/consumer
disappears, an unregistration occurs and the link is disconnected.

This kernel integration deprecates the former kvm-vfio approach:
https://lkml.org/lkml/2015/4/13/353. Some rationale about that change can
be found in IRQ bypass manager thread: https://lkml.org/lkml/2015/6/29/268

1- [PATCH v4 00/11] arm/arm64: KVM: Active interrupt state switching
for shared devices (http://www.spinics.net/lists/arm-kernel/msg437884.html)
except PATCH 11
2- [PATCH 0/6] irqchip: GICv2/v3: Add support for irq_vcpu_affinity
3- [PATCH v4] virt: IRQ bypass manager (https://lkml.org/lkml/2015/8/6/526)
4- [PATCH 0/2] KVM: arm/arm64: Guest synchronous halt/resume

All those pieces can be found at:

More backgroung on ARM IRQ forwarding in the text below and at

A forwarded IRQ is deactivated by the guest and not by the host.
When the guest deactivates the associated virtual IRQ, the interrupt
controller automatically completes the physical IRQ. Obviously
this requires some HW support in the interrupt controller. This is
the case for ARM GICv2.

The direct benefit is that, for a level sensitive IRQ, a VM exit
can be avoided on forwarded IRQ completion.

When the IRQ is forwarded, the VFIO platform driver does not need to
mask the physical IRQ anymore before signaling the eventfd. Indeed
genirq lowers the running priority, enabling other physical IRQ to hit
except that one.

Besides, the injection still is based on irqfd triggering. The only
impact on irqfd process is resamplefd is not called anymore on
virtual IRQ completion since deactivation is not trapped by KVM.

This was tested on Calxeda Midway, assigning the xgmac main IRQ


v2 (RFC) -> v3(PATCH):
- all dependencies now have a patch status
- we dropped the producer active boolean exchanged between the
VFIO producer and irqfd arm consumer. As a consequence, on
unforward, if the IRQ is active, this latter is deactivated
without VFIO-masking it. So we do not exactly come back to the
exact state where we would be in unforwarded state. A new
physical IRQ can hit while the previous virtual IRQ is under
treatment. Its injection in the guest may be rejected thanks
to the VGIC state machine. This IRQ will be lost but I don't
think this is a severe issue. In case no new IRQ hits, the
guest deactivation of the virtual IRQ will trigger the resamplefd
which will VFIO unmask the non-masked IRQ. This also has no
- VFIO platform driver consumer_add now can fail. It rejects the
transition for forwarding state in case the IRQ is active
- the series is rebased on new irq_vcpu_affinity series
- no dependency anymore on "chip/vgic adaptations for forwarded irq"
which was partially integrated into Marc's series. A fix is still
needed through.
- Guest synchronous halt/resume patch re-integrated into this series
- integrate a new patch file coming mixing
[PATCH v4 11/11] KVM: arm/arm64: vgic: Allow HW interrupts for
non-shared devices &
[RFC v2 2/4] KVM: arm: vgic: fix state machine for forwarded IRQ

v1 -> v2:
- irq bypass manager and irqfd consumer moved in a separate patch
- kvm_arm_[halt,resume]_guest moved in a separate patch
- remove VFIO external functions since we do not need them anymore
- apply container_of strategy advised by Paolo. Only active field
remains and discussions will tell whether we get rid of it.
- renamed kvm_arch functions

- kvm-vfio v6 -> RFC v1 based on IRQ bypass manager
see previous history in https://lkml.org/lkml/2015/4/13/353).

Best Regards


Eric Auger (9):
VFIO: platform: registration of a dummy IRQ bypass producer
VFIO: platform: test forwarded state when selecting the IRQ handler
VFIO: platform: single handler using function pointer
VFIO: platform: add vfio_platform_set_automasked
VFIO: platform: add vfio_platform_is_active
VFIO: platform: add irq bypass producer management
KVM: arm/arm64: vgic: support irqfd injection of a forwarded IRQ
KVM: arm/arm64: vgic: forwarding control
KVM: arm/arm64: implement IRQ bypass consumer functions

Marc Zyngier (1):
KVM: arm/arm64: vgic: Allow HW interrupts for non-shared devices

arch/arm/kvm/Kconfig | 1 +
arch/arm/kvm/arm.c | 35 +++++
arch/arm64/kvm/Kconfig | 1 +
drivers/vfio/platform/vfio_platform_irq.c | 113 +++++++++++++-
drivers/vfio/platform/vfio_platform_private.h | 4 +
include/kvm/arm_vgic.h | 12 +-
virt/kvm/arm/arch_timer.c | 3 +-
virt/kvm/arm/vgic.c | 215 ++++++++++++++++++++++++--
8 files changed, 358 insertions(+), 26 deletions(-)


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