Re: [PATCH v3 4/8] KVM: kvm-vfio: User API for IRQ forwarding

[Christoffer Dall]

On Sun, Nov 23, 2014 at 07:35:56PM +0100, Eric Auger wrote:
> This patch adds and document a new KVM_DEV_VFIO_DEVICE group

documents

> and 2 device attributes: KVM_DEV_VFIO_DEVICE_FORWARD_IRQ,
> KVM_DEV_VFIO_DEVICE_UNFORWARD_IRQ. The purpose is to be able
> to set a VFIO device IRQ as forwarded or not forwarded.
> the command takes as argument a handle to a new struct named
> kvm_arch_forwarded_irq.
> 
> Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
> 
> ---
> 
> v2 -> v3:
> - rework vfio kvm device documentation
> - reword commit message and title
> - add subindex in kvm_arch_forwarded_irq to be closer to VFIO API
> - forwarding state can only be changed with VFIO IRQ signaling is off
> 
> v1 -> v2:
> - 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
> ---
>  Documentation/virtual/kvm/devices/vfio.txt | 34 ++++++++++++++++++++++++------
>  include/uapi/linux/kvm.h                   | 10 +++++++++
>  2 files changed, 38 insertions(+), 6 deletions(-)
> 
> diff --git a/Documentation/virtual/kvm/devices/vfio.txt b/Documentation/virtual/kvm/devices/vfio.txt
> index ef51740..f7aff29 100644
> --- a/Documentation/virtual/kvm/devices/vfio.txt
> +++ b/Documentation/virtual/kvm/devices/vfio.txt
> @@ -4,15 +4,24 @@ VFIO virtual device
>  Device types supported:
>    KVM_DEV_TYPE_VFIO
>  
> -Only one VFIO instance may be created per VM.  The created device
> -tracks VFIO groups in use by the VM and features of those groups
> -important to the correctness and acceleration of the VM.  As groups
> -are enabled and disabled for use by the VM, KVM should be updated
> -about their presence.  When registered with KVM, a reference to the
> -VFIO-group is held by KVM.
> +Only one VFIO instance may be created per VM.
> +
> +The created device tracks VFIO groups in use by the VM and features
> +of those groups important to the correctness and acceleration of
> +the VM.  As groups are enabled and disabled for use by the VM, KVM
> +should be updated about their presence.  When registered with KVM,
> +a reference to the VFIO-group is held by KVM.
> +
> +The device also tracks & enable VFIO device forwarded IRQs, if any.

s/tracks & enable/tracks and enables/

> +A physical forwarded IRQ is directly completed by the guest. This
> +requires HW support in the interrupt controller which must be able
> +to automatically complete the physical IRQ when it detects the guest
> +has completed the corresponding virtual IRQ. The modality sometimes
> +is named direct EOI.

this last sentence is a bit floating out there; perhaps you want to be
more specific and say what it is on ARM.

>  
>  Groups:
>    KVM_DEV_VFIO_GROUP
> +  KVM_DEV_VFIO_DEVICE
>  
>  KVM_DEV_VFIO_GROUP attributes:
>    KVM_DEV_VFIO_GROUP_ADD: Add a VFIO group to VFIO-KVM device tracking
> @@ -20,3 +29,16 @@ KVM_DEV_VFIO_GROUP attributes:
>  
>  For each, kvm_device_attr.addr points to an int32_t file descriptor
>  for the VFIO group.
> +
> +KVM_DEV_VFIO_DEVICE attributes:
> +  KVM_DEV_VFIO_DEVICE_FORWARD_IRQ: set a VFIO device IRQ as forwarded
> +  KVM_DEV_VFIO_DEVICE_UNFORWARD_IRQ: set a VFIO device IRQ as not forwarded
> +
> +For each, kvm_device_attr.addr points to a kvm_arch_forwarded_irq struct.
> +
> +The forwarded state can only be changed when the VFIO signaling mechanism
> +for this physical IRQ is not set. In other words, forwarding must be
> +activated before VFIO_DEVICE_SET_IRQS has been called to trigger the IRQ
> +or associate an eventfd to it. Unforwarding can only be called while the
> +signaling has been disabled with VFIO_DEVICE_SET_IRQS. If this condition is
> +not satisfied, the command returns an -EBUSY.

s/command/ioctl/

> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 6076882..a269a42 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -946,6 +946,9 @@ struct kvm_device_attr {
>  #define  KVM_DEV_VFIO_GROUP			1
>  #define   KVM_DEV_VFIO_GROUP_ADD			1
>  #define   KVM_DEV_VFIO_GROUP_DEL			2
> +#define  KVM_DEV_VFIO_DEVICE			2
> +#define   KVM_DEV_VFIO_DEVICE_FORWARD_IRQ			1
> +#define   KVM_DEV_VFIO_DEVICE_UNFORWARD_IRQ			2
>  
>  enum kvm_device_type {
>  	KVM_DEV_TYPE_FSL_MPIC_20	= 1,
> @@ -963,6 +966,13 @@ enum kvm_device_type {
>  	KVM_DEV_TYPE_MAX,
>  };
>  
> +struct kvm_arch_forwarded_irq {
> +	__u32 fd; /* file desciptor of the VFIO device */
> +	__u32 index; /* VFIO device IRQ index */
> +	__u32 subindex; /* VFIO device IRQ subindex */
> +	__u32 gsi; /* gsi, ie. virtual IRQ number */
> +};
> +
>  /*
>   * ioctls for VM fds
>   */
> -- 
> 1.9.1
> 

otherwise this looks reasonable.
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