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

Wu, Feng
2014-11-17T13:45:28Z

> -----Original Message-----
> From: kvm-owner at vger.kernel.org [mailto:kvm-owner at vger.kernel.org] On
> Behalf Of Eric Auger
> Sent: Monday, November 17, 2014 9:42 PM
> To: Wu, Feng; Alex Williamson; Christoffer Dall
> Cc: eric.auger at st.com; marc.zyngier at arm.com;
> linux-arm-kernel at lists.infradead.org; kvmarm at lists.cs.columbia.edu;
> kvm at vger.kernel.org; joel.schopp at amd.com; kim.phillips at freescale.com;
> paulus at samba.org; gleb at kernel.org; pbonzini at redhat.com;
> linux-kernel at vger.kernel.org; patches at linaro.org; will.deacon at arm.com;
> a.motakis at virtualopensystems.com; a.rigo at virtualopensystems.com;
> john.liuli at huawei.com
> Subject: Re: [RFC v2 0/9] KVM-VFIO IRQ forward control
>
> Hi Feng,
>
> I will submit a PATCH v3 release end of this week.
>
> Best Regards
>
> Eric

Thanks for the update, Eric!

Thanks,
Feng

>
> On 11/17/2014 12:25 PM, Wu, Feng wrote:
> >
> >
> >> -----Original Message-----
> >> From: linux-kernel-owner at vger.kernel.org
> >> [mailto:linux-kernel-owner at vger.kernel.org] On Behalf Of Alex Williamson
> >> Sent: Thursday, September 11, 2014 1:10 PM
> >> To: Christoffer Dall
> >> Cc: Eric Auger; eric.auger at st.com; marc.zyngier at arm.com;
> >> linux-arm-kernel at lists.infradead.org; kvmarm at lists.cs.columbia.edu;
> >> kvm at vger.kernel.org; joel.schopp at amd.com; kim.phillips at freescale.com;
> >> paulus at samba.org; gleb at kernel.org; pbonzini at redhat.com;
> >> linux-kernel at vger.kernel.org; patches at linaro.org; will.deacon at arm.com;
> >> a.motakis at virtualopensystems.com; a.rigo at virtualopensystems.com;
> >> john.liuli at huawei.com
> >> Subject: Re: [RFC v2 0/9] KVM-VFIO IRQ forward control
> >>
> >> On Thu, 2014-09-11 at 05:10 +0200, Christoffer Dall wrote:
> >>> On Tue, Sep 02, 2014 at 03:05:41PM -0600, Alex Williamson wrote:
> >>>> On Mon, 2014-09-01 at 14:52 +0200, Eric Auger wrote:
> >>>>> 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 at 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
> >>>>>
> >>>>
> >>>> Have we ventured too far in the other direction? I suppose what I was
> >>>> hoping to see was something more like:
> >>>>
> >>>> case KVM_DEV_VFIO_DEVICE_FORWARD_IRQ:{
> >>>>
> >>>> /* get vfio_device */
> >>>>
> >>>> /* get mutex */
> >>>>
> >>>> /* verify device+irq isn't already forwarded */
> >>>>
> >>>> /* allocate device/forwarded irq */
> >>>>
> >>>> /* get struct device */
> >>>>
> >>>> /* callout to arch code passing struct device, gsi, ... */
> >>>>
> >>>> /* if success, add to kv, else free and error */
> >>>>
> >>>> /* mutex unlock */
> >>>> }
> >>>
> >>> I think that's essentially what this patch set is trying to do, but
> >>> there are just too many complicated intertwining cases right now that
> >>> makes the code hard to read.
> >>>
> >>>>
> >>>> Exposing the internal mutex out to arch code, as in v1, was an
> >>>> indication that we were pushing too much out to arch code, but including
> >>>> platform_device.h into virt/kvm/vfio.c tells me we're still not
> >>>> abstracting at the right point. Thanks,
> >>>>
> >>> I raised my eyebrows over the platform device bus thingy here as well,
> >>> but on the other hand, there's nothing ARM-specific about referring to
> >>> the platform device bus.
> >>>
> >>> I think perhaps it just has to be made more clear that the generic code
> >>> deals with translating the device resources in the necessary way, and
> >>> currently it only supports vfio-platform devices?
> >>
> >> Ok, you're probably right, looking at it again it is closer than I
> >> thought. At the same time, the use of platform device in
> >> virt/kvm/vfio.c is pointless and can easily be pushed out to the arch
> >> code as just another error return case. vfio.c doesn't need to be aware
> >> of hwirq. The rest of the code is just overly complicated, with three
> >> different cleanup functions and validation function bloat. Thanks,
> >>
> >> Alex
> >
> >
> > Hi Alex, Could you please tell what is the current status of this patch set.
> > As you mentioned in another thread, something(such as,
> kvm_vfio_device_get_external_user(), etc.)
> > in this patch set can be leveraged for VT-d Posted-interrtups.
> >
> > Thanks,
> > Feng
> >
> >>
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