[RFC v2 0/9] KVM-VFIO IRQ forward control

[Eric Auger]

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

It enables to transform a VFIO platform driver IRQ into a forwarded
IRQ. The direct benefit is that, for a level sensitive IRQ, a VM
switch can be avoided on guest virtual IRQ completion. Before this
patch, a maintenance IRQ was triggered on the virtual IRQ completion.

When the IRQ is forwarded, the VFIO platform driver does not need to
disable the IRQ anymore. Indeed when returning from the IRQ handler
the IRQ is not deactivated. Only its priority is lowered. This means
the same IRQ cannot hit before the guest completes the virtual IRQ
and the GIC automatically deactivates the corresponding physical IRQ.

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 serie 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 new
KVM-VFIO device commands, KVM_DEV_VFIO_DEVICE_(UN)FORWARD_IRQ
and the capability can be checked with KVM_HAS_DEVICE_ATTR.
Assignment can only be changed when the physical IRQ is not active.
It is the responsability of the user to do this check.

This patch serie has the following dependencies:
- "ARM: Forwarding physical interrupts to a guest VM"
  (http://lwn.net/Articles/603514/) in
- [PATCH v3] irqfd for ARM
- and obviously the VFIO platform driver serie:
  [RFC PATCH v6 00/20] VFIO support for platform devices on ARM
  https://www.mail-archive.com/kvm@vger.kernel.org/msg103247.html

Integrated pieces can be found at
ssh://git.linaro.org/people/eric.auger/linux.git
on branch 3.17rc3_irqfd_forward_integ_v2

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

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
- ASSIGN/DEASSIGN renamed into FORWARD/UNFORWARD
- 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
- __KVM_HAVE_ARCH_KVM_VFIO renamed into __KVM_HAVE_ARCH_KVM_VFIO_FORWARD

Eric Auger (8):
  KVM: ARM: VGIC: fix multiple injection of level sensitive forwarded
    IRQ
  KVM: ARM: VGIC: add forwarded irq rbtree lock
  VFIO: platform: handler tests whether the IRQ is forwarded
  KVM: KVM-VFIO: update user API to program forwarded IRQ
  VFIO: Extend external user API
  KVM: KVM-VFIO: add new VFIO external API hooks
  KVM: KVM-VFIO: generic KVM_DEV_VFIO_DEVICE command and IRQ forwarding
    control
  KVM: KVM-VFIO: ARM forwarding control

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

 Documentation/virtual/kvm/devices/vfio.txt |  26 ++
 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                |  85 +++++
 drivers/vfio/platform/vfio_platform_irq.c  |   7 +-
 drivers/vfio/vfio.c                        |  24 ++
 include/kvm/arm_vgic.h                     |   1 +
 include/linux/kvm_host.h                   |  27 ++
 include/linux/vfio.h                       |   3 +
 include/uapi/linux/kvm.h                   |   9 +
 virt/kvm/arm/vgic.c                        |  59 +++-
 virt/kvm/vfio.c                            | 497 ++++++++++++++++++++++++++++-
 13 files changed, 733 insertions(+), 17 deletions(-)
 create mode 100644 arch/arm/kvm/kvm_vfio_arm.c

-- 
1.9.1