Re: [Qemu-devel] [RFC PATCH v2 0/4] kvm: Make ioeventfd usable on s390.

[Michael S. Tsirkin]

On Fri, Feb 22, 2013 at 01:09:45PM +0100, Cornelia Huck wrote:
> Here's the second attempt at implementing ioeventfd for s390.
> 
> Rather than the architecture-specific functions used in v1, we
> now try to integrate with the kvm_io_device infrastructure.
> Calls to diagnose 500 subcode 3 are now mapped to _write.
> These devices are created on a new KVM_CSS_BUS when using a
> new flag KVM_IOEVENTFD_FLAG_CSS. addr and datamatch are (ab)used
> to contain the subchannel id and the virtqueue.

OK so a question: qemu has:

        #define KVM_S390_VIRTIO_NOTIFY          0
        #define KVM_S390_VIRTIO_RESET           1
        #define KVM_S390_VIRTIO_SET_STATUS      2
        #define KVM_S390_VIRTIO_CCW_NOTIFY      3

So this is really s390_virtio_ccw not generally css?
Maybe should say so in all headers.

> we want to attach other hypercalls or carry more payload.
> 
> Another limitation is the limit of 1000 io devices per bus, which
> we would hit easily with a few hundred devices, but that should
> be fixable.
> 
> v1 -> v2:
> - Move irqfd initialization from a module init function to kvm_init,
>   eliminating the need for a second module for kvm/s390.
> - Use kvm_io_device for s390 css devices.
> 
> 
> Cornelia Huck (4):
>   KVM: Initialize irqfd from kvm_init().
>   KVM: Introduce KVM_CSS_BUS.
>   KVM: ioeventfd for s390 css devices.
>   KVM: s390: Wire up ioeventfd.
> 
>  Documentation/virtual/kvm/api.txt |  7 +++++++
>  arch/s390/kvm/Kconfig             |  1 +
>  arch/s390/kvm/Makefile            |  2 +-
>  arch/s390/kvm/diag.c              | 25 +++++++++++++++++++++++++
>  arch/s390/kvm/kvm-s390.c          |  1 +
>  include/linux/kvm_host.h          | 14 ++++++++++++++
>  include/uapi/linux/kvm.h          |  2 ++
>  virt/kvm/eventfd.c                | 15 ++++++++-------
>  virt/kvm/kvm_main.c               |  6 ++++++
>  9 files changed, 65 insertions(+), 8 deletions(-)
> 
> -- 
> 1.7.12.4