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

[Wu, Feng]

> -----Original Message-----
> From: Eric Auger [mailto:eric.auger@xxxxxxxxxx]
> Sent: Monday, November 24, 2014 2:36 AM
> To: eric.auger@xxxxxx; eric.auger@xxxxxxxxxx; christoffer.dall@xxxxxxxxxx;
> marc.zyngier@xxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> kvmarm@xxxxxxxxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx;
> alex.williamson@xxxxxxxxxx; joel.schopp@xxxxxxx;
> kim.phillips@xxxxxxxxxxxxx; paulus@xxxxxxxxx; gleb@xxxxxxxxxx;
> pbonzini@xxxxxxxxxx; agraf@xxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx; patches@xxxxxxxxxx; will.deacon@xxxxxxx;
> a.motakis@xxxxxxxxxxxxxxxxxxxxxx; a.rigo@xxxxxxxxxxxxxxxxxxxxxx;
> john.liuli@xxxxxxxxxx; ming.lei@xxxxxxxxxxxxx; Wu, Feng
> Subject: [PATCH v3 0/8] KVM-VFIO IRQ forward control
> 
> This series 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.
> 
> 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
> controler.
> 
> 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
> attributes:
> - KVM_DEV_VFIO_DEVICE_FORWARD_IRQ,
> - KVM_DEV_VFIO_DEVICE_UNFORWARD_IRQ.
> 
> 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"
>   (http://lwn.net/Articles/603514/)
> - [PATCH v9 00/19] VFIO support for platform and AMBA devices on ARM
>   (http://www.spinics.net/lists/kvm-arm/msg11745.html)
> - [PATCH v2 0/6] vfio: type1: support for ARM SMMUS with
> VFIO_IOMMU_TYPE1
>   (http://www.spinics.net/lists/kvm-arm/msg11738.html)
> 
> Integrated pieces can be found at
> ssh://git.linaro.org/people/eric.auger/linux.git
> on branch irqfd_integ_v8
> 
> This was was tested on Calxeda Midway, assigning the xgmac main IRQ.
> 

Hi Eric,

Did you send out the latest QEMU part for this patch set, I notice that v6 of
The QEMU part is sent out, but seems some structure in this new version
has been changed, such as, struct kvm_arch_forwarded_irq (subindex is added
in this version), so a new patchset in QEMU is also needed.

Thanks,
Feng


> 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
> - 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 (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
> 
> --
> 1.9.1

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