Re: [Qemu-devel] [PATCH v6 00/16] KVM platform device passthrough

[Eric Auger]

On 09/16/2014 10:51 PM, Alex Williamson wrote:
> On Tue, 2014-09-16 at 00:01 +0200, Eric Auger wrote:
>> On 09/12/2014 01:05 AM, Christoffer Dall wrote:
>>> On Thu, Sep 11, 2014 at 04:51:14PM -0600, Alex Williamson wrote:
>>>> On Thu, 2014-09-11 at 15:23 -0700, Christoffer Dall wrote:
>>>>> On Thu, Sep 11, 2014 at 04:14:09PM -0600, Alex Williamson wrote:
>>>>>> On Tue, 2014-09-09 at 08:31 +0100, Eric Auger wrote:
>>>>>>> This RFC series aims at enabling KVM platform device passthrough.
>>>>>>> It implements a VFIO platform device, derived from VFIO PCI device.
>>>>>>>
>>>>>>> The VFIO platform device uses the host VFIO platform driver which must
>>>>>>> be bound to the assigned device prior to the QEMU system start.
>>>>>>>
>>>>>>> - the guest can directly access the device register space
>>>>>>> - assigned device IRQs are transparently routed to the guest by
>>>>>>>   QEMU/KVM (3 methods currently are supported: user-level eventfd
>>>>>>>   handling, irqfd, forwarded IRQs)
>>>>>>> - iommu is transparently programmed to prevent the device from
>>>>>>>   accessing physical pages outside of the guest address space
>>>>>>>
>>>>>>> This patch series is made of the following patch files:
>>>>>>>
>>>>>>> 1-7) Modifications to PCI code to prepare for VFIO platform device
>>>>>>> 8) split of PCI specific code and generic code (move)
>>>>>>> 9-11) creation of the VFIO calxeda xgmac platform device, without irqfd
>>>>>>>       support (MMIO direct access and IRQ assignment).
>>>>>>> 12) fake injection test modality (to test multiple IRQ)
>>>>>>> 13) addition of irqfd/virqfd support
>>>>>>> 14-16) forwarded IRQ
>>>>>>>
>>>>>>> Dependency List:
>>>>>>>
>>>>>>> QEMU dependencies:
>>>>>>> [1] [PATCH v2 0/9] Dynamic sysbus device allocation support, Alex Graf
>>>>>>>     http://lists.gnu.org/archive/html/qemu-ppc/2014-07/msg00047.html
>>>>>>> [2] [RFC v3] machvirt dynamic sysbus device instantiation, Eric Auger
>>>>>>> [3] [PATCH v2 0/2] actual checks of KVM_CAP_IRQFD and 
>>>>>>> KVM_CAP_IRQFD_RESAMPLE,
>>>>>>>     Eric Auger
>>>>>>>     
>>>>>>> http://lists.nongnu.org/archive/html/qemu-devel/2014-09/msg00589.html
>>>>>>> [4] [RFC] vfio: migration to trace points, Eric Auger
>>>>>>>     
>>>>>>> http://lists.nongnu.org/archive/html/qemu-devel/2014-09/msg00569.html
>>>>>>>
>>>>>>> Kernel Dependencies:
>>>>>>> [5] [RFC Patch v6 0/20] VFIO support for platform devices, Antonios 
>>>>>>> Motakis
>>>>>>>     https://www.mail-archive.com/address@hidden/msg103247.html
>>>>>>> [6] [PATCH v3] ARM: KVM: add irqfd support, Eric Auger
>>>>>>>     https://lkml.org/lkml/2014/9/1/141
>>>>>>> [7] arm/arm64: KVM: Various VGIC cleanups and improvements, Christoffer 
>>>>>>> Dall
>>>>>>>     http://comments.gmane.org/gmane.linux.ports.arm.kernel/340430
>>>>>>> [8] [RFC v2 0/9] KVM-VFIO IRQ forward control, Eric Auger
>>>>>>>     https://lkml.org/lkml/2014/9/1/344
>>>>>>> [9] [RFC PATCH 0/9] ARM: Forwarding physical interrupts to a guest VM,
>>>>>>>     Marc Zyngier
>>>>>>>     http://lwn.net/Articles/603514/
>>>>>>>
>>>>>>> kernel pieces can be found at:
>>>>>>> http://git.linaro.org/people/eric.auger/linux.git
>>>>>>> (branch 3.17rc3_irqfd_forward_integ_v2)
>>>>>>> QEMU pieces can be found at:
>>>>>>> http://git.linaro.org/people/eric.auger/qemu.git (branch vfio_integ_v6)
>>>>>>>
>>>>>>> The patch series was tested on Calxeda Midway (ARMv7) where one xgmac
>>>>>>> is assigned to KVM host while the second one is assigned to the guest.
>>>>>>> Reworked PCI device is not tested.
>>>>>>>
>>>>>>> Wiki for Calxeda Midway setup:
>>>>>>> https://wiki.linaro.org/LEG/Engineering/Virtualization/Platform_Device_Passthrough_on_Midway
>>>>>>>
>>>>>>> History:
>>>>>>>
>>>>>>> v5->v6:
>>>>>>> - rebase on 2.1rc5 PCI code
>>>>>>> - forwarded IRQ first integraton
>>>>>>
>>>>>> Why?  Are there acceleration paths that you're concerned cannot be
>>>>>> implemented or we do not already have a proof of concept for?  The base
>>>>>> kernel patch series you depend on is 3 months old yet this series
>>>>>> continues to grow and add new dependencies.  Please let's prioritize
>>>>>> getting something upstream instead of adding more blockers to prevent
>>>>>> that.  Thanks,
>>>>>>
>>>>> I'm not exactly sure what this changelog line was referring to
>>>>> (depending on Marc's forwarding IRQ patches?), but just want to add that
>>>>> there are a number of dependencies for the GIC that need to go in as
>>>>> well (should happen within a few weeks), but I think it's unlikely that
>>>>> the IRQ forwarding stuff goes in for v3.18 at this point.
>>>>>
>>>>> It may make sense as you suggest to keep that part out of this patch set
>>>>> and something merged sooner as opposed to later, but I'm too jet-lagged
>>>>> to completely understand if that's going to be a horrible mess.
>>>>
>>>> The point is that we're on v6 of a patch series and its first non-RFC
>>>> posting and we're rolling in a first pass at a QEMU implementation that
>>>> depends on a contested kernel RFC, which depends on another stagnant
>>>> kernel RFC.  I'm fine with working on it in parallel, but give me some
>>>> light at the end of the tunnel as a reviewer and maintainer that this
>>>> code isn't going to live indefinitely on the mailing list.  Do we really
>>>> need those GIC patches do be able to have non-KVM accelerated VFIO
>>>> platform device assignment?  We certainly don't need IRQ forwarding.
>>>> Thanks,
>>
>> Hi Alex,
>>
>> Sorry for the delay, I was travelling.
>>
>> I understand your impatience. I personally would be happy if we could
>> envision upstreaming this patch in several steps. Let me know if it
>> makes sense.
>>
>> STEP I:  integrate 1 - 11: leads to have a non-KVM accelerated VFIO QEMU
>> device. 12 can be part of it too but since it is a test feature this one
>> might be dropped. just let me know what you think.
> 
> I'd probably drop 12.  Is that really something that's useful in
> upstream code?  It's a good use of the vfio loopback interrupt and good
> testing, but do you really want to maintain it in the code?  Is it
> sufficient that it's been posted to the mailing list so you can find and
> re-apply it if you want to do similar testing again?
Hi Alex,

yes I agree with you about dropping it.

> 
>> depends on:
>> QEMU:
>> [1] [PATCH v2 0/9] Dynamic sysbus device allocation support, A. Graf
>> http://lists.gnu.org/archive/html/qemu-ppc/2014-07/msg00047.html
>> [2] [RFC v3] machvirt dynamic sysbus device instantiation, E. Auger
>> [4] [RFC] vfio: migration to trace points, E. Auger
>> http://lists.nongnu.org/archive/html/qemu-devel/2014-09/msg00569.html
>> KERNEL:
>> [5] [RFC Patch v6 0/20] VFIO support for platform devices, A. Motakis
>> https://www.mail-archive.com/address@hidden/msg103247.html
> 
> Ok, so let's start whittling down these dependencies.  Trace points
> shouldn't be any kind of blocker, you'll just need to teach me how to
> use them and post a non-RFC patch ;)

Yes sure I will write some instructions. I need to investigate the
parser issues related to parenthesis (either fix it myself or ask
Stefan's help).

  At this point I don't even
> remember the comments for the v6 VFIO kernel support for platform
> devices.  I hope we're close enough that the next version can be sent as
> non-RFC.  It might be a good idea to pick a target kernel version and
> start working towards it.  v3.18 is probably not a realistic goal at
> this point.  I don't know about the rest, but at least the remaining
> series is non-RFC and the other is only a single patch.

On my side I will iterate rapidly on both
[2] [RFC v3] machvirt dynamic sysbus device instantiation and
[6] [PATCH v3] ARM: KVM: add irqfd support

> 
>> Step II: integrate 13: kvm-accelerated QEMU VFIO device featuring
>> iqrfd/virqfd
>>
>> depends on
>> [7] arm/arm64: KVM: Various VGIC cleanups and improvements, C. Dall
>> [6] [PATCH v3] ARM: KVM: add irqfd support, E. Auger
>> https://lkml.org/lkml/2014/9/1/141
>>
>> Step III: integrate > 13:  kvm-accelerated QEMU VFIO device featuring
>> forwarded IRQs:
>> [8] [RFC v2 0/9] KVM-VFIO IRQ forward control, Eric Auger
>> https://lkml.org/lkml/2014/9/1/344
>> [9] [RFC PATCH 0/9] ARM: Forwarding physical interrupts to a guest VM,
>> Marc Zyngier, http://lwn.net/Articles/603514/
>>
>> To me these 3 steps are quite independent from each other.
> 
> Yep, I agree.  Let's not get bogged down in letting these additional
> features interfere with progress on the base support.
> 
>> with respect to performance I think we have something reasonable now
>> with irqfd and forwarded IRQ so I do not expect any new features added
>> soon.
>>
>> from now on, I do not plan to add any new patch file to this series but
>> just correct/modify according to comments & weaknesses.
>>
>> I Hope it clarifies plans. Please let me know.
> 
> Thanks, it does.  We have several players in the VFIO platform space and
> I want to make sure we're aligned on a goal of getting code upstream,
> not just posting it to the list.  Thanks for the breakdown and your work
> towards getting those dependencies resolved.
Thanks

Eric
> 
> Alex
>