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

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Date:	Mon, 25 Aug 2014 15:27:35 +0200
From:	Eric Auger <eric.auger@...aro.org>
To:	eric.auger@...com, eric.auger@...aro.org,
	christoffer.dall@...aro.org, marc.zyngier@....com,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
	kvm@...r.kernel.org, alex.williamson@...hat.com,
	joel.schopp@....com, kim.phillips@...escale.com
Cc:	linux-kernel@...r.kernel.org, patches@...aro.org,
	will.deacon@....com, a.motakis@...tualopensystems.com,
	a.rigo@...tualopensystems.com, john.liuli@...wei.com
Subject: [RFC 0/9] KVM-VFIO IRQ forward control

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 KVM-VFIO is extended with an architecture specific implementation.
IRQ forward control is implemented in the ARM specific part.

from a user point of view, the functionality is provided through new
KVM-VFIO device commands, KVM_DEV_VFIO_DEVICE_(DE)ASSIGN_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 v2] irqfd for ARM
  which itself depends on
  - arm/arm64: KVM: Various VGIC cleanups and improvements
    http://lists.infradead.org/pipermail/linux-arm-kernel/2014-June/263685.html
- 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
git://git.linaro.org/people/eric.auger/linux.git
on branch 3.17rc1_forward_integ_v0

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

Eric Auger (9):
  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: allow arch specific implementation
  KVM: KVM-VFIO: add new VFIO external API hooks
  KVM: KVM-VFIO: add kvm_vfio_arch_data and accessors
  KVM: KVM_VFIO: ARM: implement irq forwarding control

 Documentation/virtual/kvm/devices/vfio.txt |  25 ++
 arch/arm/include/asm/kvm_host.h            |  16 +
 arch/arm/include/uapi/asm/kvm.h            |   6 +
 arch/arm/kvm/Makefile                      |   2 +-
 arch/arm/kvm/kvm_vfio_arm.c                | 599 +++++++++++++++++++++++++++++
 drivers/vfio/platform/vfio_platform_irq.c  |   7 +-
 drivers/vfio/vfio.c                        |  35 ++
 include/kvm/arm_vgic.h                     |   1 +
 include/linux/kvm_host.h                   |  30 ++
 include/linux/vfio.h                       |   4 +
 include/uapi/linux/kvm.h                   |   3 +
 virt/kvm/arm/vgic.c                        |  55 ++-
 virt/kvm/vfio.c                            |  92 +++++
 13 files changed, 862 insertions(+), 13 deletions(-)
 create mode 100644 arch/arm/kvm/kvm_vfio_arm.c

-- 
1.9.1

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