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

[Eric Auger]

On 11/24/2014 09:14 AM, Wu, Feng wrote:
> 
> 
>> -----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.

Hi Feng,

v7 is available at:
http://lists.gnu.org/archive/html/qemu-devel/2014-10/msg03804.html. It
already illustrates KVM-VFIO device usage.

v8 which will indeed integrate subindex addition will be delivered this
week.

Best Regards

Eric
> 
> 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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