linux-kernel - Re: [v4 08/16] KVM: kvm-vfio: User API for IRQ forwarding

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Date:	Thu, 11 Jun 2015 15:37:35 +0200
From:	Eric Auger <eric.auger@...aro.org>
To:	Feng Wu <feng.wu@...el.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
CC:	pbonzini@...hat.com, mtosatti@...hat.com,
	alex.williamson@...hat.com
Subject: Re: [v4 08/16] KVM: kvm-vfio: User API for IRQ forwarding

Hi Feng,
On 06/11/2015 12:51 PM, Feng Wu wrote:
> From: Eric Auger <eric.auger@...aro.org>
> 
> This patch adds and documents a new KVM_DEV_VFIO_DEVICE group
> 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_vfio_dev_irq.
> 
> Signed-off-by: Eric Auger <eric.auger@...aro.org>
> ---
>  Documentation/virtual/kvm/devices/vfio.txt | 34 ++++++++++++++++++++++++------
>  include/uapi/linux/kvm.h                   | 12 +++++++++++
>  2 files changed, 40 insertions(+), 6 deletions(-)
> 
> diff --git a/Documentation/virtual/kvm/devices/vfio.txt b/Documentation/virtual/kvm/devices/vfio.txt
> index ef51740..6186e6d 100644
> --- a/Documentation/virtual/kvm/devices/vfio.txt
> +++ b/Documentation/virtual/kvm/devices/vfio.txt
> @@ -4,15 +4,20 @@ 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 enables to control some IRQ settings of VFIO devices:
> +forwarding/posting.
>  
>  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 +25,20 @@ 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_vfio_dev_irq struct.
> +
> +When forwarded, a physical IRQ is completed by the guest and not by the
> +host. This requires HW support in the interrupt controller.
> +
> +Forwarding can only be set when the corresponding VFIO IRQ is not masked
> +(would it be through VFIO_DEVICE_SET_IRQS command or as a consequence of this
> +IRQ being currently handled) or active at interrupt controller level.
> +In such a situation, -EAGAIN is returned. It is advised to to set the
> +forwarding before the VFIO signaling is set up, this avoids trial and errors.
> +
> +Unforwarding can happen at any time.
Unfortunately the above text is out of context of your series. If it
simplifies things take the ownership of that patch file and remove my
description of KVM_DEV_VFIO_DEVICE_FORWARD_IRQ.
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 4b60056..798f3e4 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -999,6 +999,9 @@ 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
same here
Best Regards

Eric
>  
>  enum kvm_device_type {
>  	KVM_DEV_TYPE_FSL_MPIC_20	= 1,
> @@ -1018,6 +1021,15 @@ enum kvm_device_type {
>  	KVM_DEV_TYPE_MAX,
>  };
>  
> +struct kvm_vfio_dev_irq {
> +	__u32	argsz;		/* structure length */
> +	__u32	fd;		/* file descriptor of the VFIO device */
> +	__u32	index;		/* VFIO device IRQ index */
> +	__u32	start;		/* start of subindex range */
> +	__u32	count;		/* size of subindex range */
> +	__u32	gsi[];		/* gsi, ie. virtual IRQ number */
> +};
> +
>  /*
>   * ioctls for VM fds
>   */
> 

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