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

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Date:	Thu, 11 Jun 2015 22:59:00 +0300
From:	Avi Kivity <avi.kivity@...il.com>
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, eric.auger@...aro.org
Subject: Re: [v4 08/16] KVM: kvm-vfio: User API for IRQ forwarding

On 06/11/2015 01:51 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.

Is there no way to do this automatically?  After all, vfio knows that a 
device interrupt is forwarded to some eventfd, and kvm knows that some 
eventfd is forwarded to a guest interrupt.  If they compare notes 
through a central registry, they can figure out that the interrupt needs 
to be forwarded.


> 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.
> 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
>   
>   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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