Re: [PATCH 0/5] vfio/spapr: Handle changes of master irq chip for VFIO devices

[Alex Williamson]

On Thu, 21 Nov 2019 11:56:02 +1100
David Gibson <address@hidden> wrote:

> Due to the way feature negotiation works in PAPR (which is a
> paravirtualized platform), we can end up changing the global irq chip
> at runtime, including it's KVM accelerate model.  That causes
> complications for VFIO devices with INTx, which wire themselves up
> directly to the KVM irqchip for performance.
> 
> This series introduces a new notifier to let VFIO devices (and
> anything else that needs to in the future) know about changes to the
> master irqchip.  It modifies VFIO to respond to the notifier,
> reconnecting itself to the new KVM irqchip as necessary.
> 
> In particular this removes a misleading (though not wholly inaccurate)
> warning that occurs when using VFIO devices on a pseries machine type
> guest.
> 
> Open question: should this go into qemu-4.2 or wait until 5.0?  It's
> has medium complexity / intrusiveness, but it *is* a bugfix that I
> can't see a simpler way to fix.  It's effectively a regression from
> qemu-4.0 to qemu-4.1 (because that introduced XIVE support by
> default), although not from 4.1 to 4.2.

Looks reasonable to me for 4.2, the vfio changes are not as big as they
appear.  If Paolo approves this week, I can send a pull request,
otherwise I can leave my ack for someone else as I'll be on PTO/holiday
next week.  Thanks,

Alex
 
> Changes since RFC:
>  * Fixed some incorrect error paths pointed by aw in 3/5
>  * 5/5 had some problems previously, but they have been obsoleted by
>    other changes merged in the meantime
> 
> David Gibson (5):
>   kvm: Introduce KVM irqchip change notifier
>   vfio/pci: Split vfio_intx_update()
>   vfio/pci: Respond to KVM irqchip change notifier
>   spapr: Handle irq backend changes with VFIO PCI devices
>   spapr: Work around spurious warnings from vfio INTx initialization
> 
>  accel/kvm/kvm-all.c    | 18 ++++++++++++
>  accel/stubs/kvm-stub.c | 12 ++++++++
>  hw/ppc/spapr_irq.c     | 17 +++++++++++-
>  hw/vfio/pci.c          | 62 +++++++++++++++++++++++++++---------------
>  hw/vfio/pci.h          |  1 +
>  include/sysemu/kvm.h   |  5 ++++
>  6 files changed, 92 insertions(+), 23 deletions(-)
>