[PATCH v3 0/8] KVM-VFIO IRQ forward control

From: Eric Auger
Date: Sun Nov 23 2014 - 13:41:23 EST

This series proposes an integration of "ARM: Forwarding physical
interrupts to a guest VM" (http://lwn.net/Articles/603514/) in

It enables to transform a VFIO platform driver IRQ into a forwarded

When a physical IRQ is forwarded (to a guest), the host does not
deactivates this latter. Completion ownership is transferred to the
guest. When the guest deactivates the associated virtual IRQ,
the interrupt controler automatically completes the physical IRQ.
Obviously this requires some dedicated HW support in the interrupt

The direct benefit is that, for a level sensitive IRQ, it avoids a
VM exit 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 this latter becomes "transparent".

The current integration is based on an extension of the KVM-VFIO
device, previously used by KVM to interact with VFIO groups. The
patch series now enables KVM to directly interact with a VFIO
platform device. The VFIO external API was extended for that purpose.

Th KVM-VFIO device can get/put the vfio platform device, check its
integrity and type, get the IRQ number associated to an IRQ index.

The IRQ forward programming is architecture specific (virtual interrupt
controller programming basically). However the whole infrastructure is
kept generic.

from a user point of view, the functionality is provided through a
new KVM-VFIO group named KVM_DEV_VFIO_DEVICE and 2 associated

The capability can be checked with KVM_HAS_DEVICE_ATTR.

Forwarding must be activated before VFIO signaling mechanism is set
using VFIO_DEVICE_SET_IRQS and unset while the signaling is disabled.


This patch series has the following dependencies:
- "ARM: Forwarding physical interrupts to a guest VM"
- [PATCH v9 00/19] VFIO support for platform and AMBA devices on ARM
- [PATCH v2 0/6] vfio: type1: support for ARM SMMUS with VFIO_IOMMU_TYPE1

Integrated pieces can be found at
on branch irqfd_integ_v8

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

v2 -> v3:
- kvm_fwd_irq_action enum replaced by a bool (KVM_VFIO_IRQ_CLEANUP does not
exist anymore)
- a new struct local to vfio.c was introduced to wrap kvm_fw_irq and make it
linkable: kvm_vfio_fwd_irq_node
- kvm_fwd_irq now is self-contained (includes struct vfio_device *)
- a single list of kvm_vfio_fwd_irq_irq_node is used instead of having
a list of devices and a list of forward irq per device. Having 2 lists
brought extra complexity.
- the VFIO device ref counter is incremented each time a new IRQ is forwarded.
It is not attempted anymore to hold a single reference whatever the number
of forwarded IRQs.
- subindex added on top of index to be closer to VFIO API
- platform device check moved in the arm specific implementation
- enable the KVM-VFIO device for arm64
- forwarded state change only can happen while the VFIO IRQ handler is not
set; in other words, when the VFIO IRQ signaling is not set.

v1 -> v2:
- forward control is moved from architecture specific file into generic
vfio.c module.
only kvm_arch_set_fwd_state remains architecture specific
- integrate Kim's patch which enables KVM-VFIO for ARM
- fix vgic state bypass in vgic_queue_hwirq
- struct kvm_arch_forwarded_irq moved from arch/arm/include/uapi/asm/kvm.h
to include/uapi/linux/kvm.h
also irq_index renamed into index and guest_irq renamed into gsi
- vfio_external_get_base_device renamed into vfio_external_base_device
- vfio_external_get_type removed
- kvm_vfio_external_get_base_device renamed into kvm_vfio_external_base_device

Eric Auger (7):
KVM: arm64: Enable the KVM-VFIO device
VFIO: platform: forwarded state tested when selecting IRQ handler
KVM: kvm-vfio: User API for IRQ forwarding
VFIO: External user API device helpers
KVM: kvm-vfio: wrapper to VFIO external API device helpers
KVM: kvm-vfio: generic forwarding control
KVM: arm: kvm-vfio: forwarding control

Kim Phillips (1):
KVM: arm: Enable the KVM-VFIO device

Documentation/virtual/kvm/devices/vfio.txt | 34 +++-
arch/arm/include/asm/kvm_host.h | 7 +
arch/arm/kvm/Kconfig | 1 +
arch/arm/kvm/Makefile | 4 +-
arch/arm/kvm/kvm_vfio_arm.c | 101 ++++++++++
arch/arm64/kvm/Kconfig | 1 +
arch/arm64/kvm/Makefile | 2 +-
drivers/vfio/platform/vfio_platform_irq.c | 7 +-
drivers/vfio/vfio.c | 24 +++
include/linux/kvm_host.h | 28 +++
include/linux/vfio.h | 3 +
include/uapi/linux/kvm.h | 10 +
virt/kvm/vfio.c | 294 ++++++++++++++++++++++++++++-
13 files changed, 503 insertions(+), 13 deletions(-)
create mode 100644 arch/arm/kvm/kvm_vfio_arm.c


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