Commit 6cdd9782 authored by Alexey Kardashevskiy's avatar Alexey Kardashevskiy Committed by Alex Williamson
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vfio: add external user support 



VFIO is designed to be used via ioctls on file descriptors
returned by VFIO.

However in some situations support for an external user is required.
The first user is KVM on PPC64 (SPAPR TCE protocol) which is going to
use the existing VFIO groups for exclusive access in real/virtual mode
on a host to avoid passing map/unmap requests to the user space which
would made things pretty slow.

The protocol includes:

1. do normal VFIO init operation:
	- opening a new container;
	- attaching group(s) to it;
	- setting an IOMMU driver for a container.
When IOMMU is set for a container, all groups in it are
considered ready to use by an external user.

2. User space passes a group fd to an external user.
The external user calls vfio_group_get_external_user()
to verify that:
	- the group is initialized;
	- IOMMU is set for it.
If both checks passed, vfio_group_get_external_user()
increments the container user counter to prevent
the VFIO group from disposal before KVM exits.

3. The external user calls vfio_external_user_iommu_id()
to know an IOMMU ID. PPC64 KVM uses it to link logical bus
number (LIOBN) with IOMMU ID.

4. When the external KVM finishes, it calls
vfio_group_put_external_user() to release the VFIO group.
This call decrements the container user counter.
Everything gets released.

The "vfio: Limit group opens" patch is also required for the consistency.

Signed-off-by: default avatarAlexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: default avatarAlex Williamson <alex.williamson@redhat.com>
parent c095ba72

drivers/vfio/vfio.c

+62 −0
Original line number Diff line number Diff line
@@ -1352,6 +1352,68 @@ static const struct file_operations vfio_device_fops = { 
	.mmap		= vfio_device_fops_mmap,

};



/**

 * External user API, exported by symbols to be linked dynamically.

 *

 * The protocol includes:

 *  1. do normal VFIO init operation:

 *	- opening a new container;

 *	- attaching group(s) to it;

 *	- setting an IOMMU driver for a container.

 * When IOMMU is set for a container, all groups in it are

 * considered ready to use by an external user.

 *

 * 2. User space passes a group fd to an external user.

 * The external user calls vfio_group_get_external_user()

 * to verify that:

 *	- the group is initialized;

 *	- IOMMU is set for it.

 * If both checks passed, vfio_group_get_external_user()

 * increments the container user counter to prevent

 * the VFIO group from disposal before KVM exits.

 *

 * 3. The external user calls vfio_external_user_iommu_id()

 * to know an IOMMU ID.

 *

 * 4. When the external KVM finishes, it calls

 * vfio_group_put_external_user() to release the VFIO group.

 * This call decrements the container user counter.

 */

struct vfio_group *vfio_group_get_external_user(struct file *filep)

{

	struct vfio_group *group = filep->private_data;



	if (filep->f_op != &vfio_group_fops)

		return ERR_PTR(-EINVAL);



	if (!atomic_inc_not_zero(&group->container_users))

		return ERR_PTR(-EINVAL);



	if (!group->container->iommu_driver ||

			!vfio_group_viable(group)) {

		atomic_dec(&group->container_users);

		return ERR_PTR(-EINVAL);

	}



	vfio_group_get(group);



	return group;

}

EXPORT_SYMBOL_GPL(vfio_group_get_external_user);



void vfio_group_put_external_user(struct vfio_group *group)

{

	vfio_group_put(group);

	vfio_group_try_dissolve_container(group);

}

EXPORT_SYMBOL_GPL(vfio_group_put_external_user);



int vfio_external_user_iommu_id(struct vfio_group *group)

{

	return iommu_group_id(group->iommu_group);

}

EXPORT_SYMBOL_GPL(vfio_external_user_iommu_id);



/**

 * Module/class support

 */

include/linux/vfio.h

+7 −0
Original line number Diff line number Diff line
@@ -90,4 +90,11 @@ extern void vfio_unregister_iommu_driver( 
	TYPE tmp;						\

	offsetof(TYPE, MEMBER) + sizeof(tmp.MEMBER); })		\



/*

 * External user API

 */

extern struct vfio_group *vfio_group_get_external_user(struct file *filep);

extern void vfio_group_put_external_user(struct vfio_group *group);

extern int vfio_external_user_iommu_id(struct vfio_group *group);



#endif /* VFIO_H */

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