Re: [PATCH kernel 14/15] vfio/spapr_tce: Export container API for external users

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 9 Aug 2016 15:19:39 +1000
Alexey Kardashevskiy <aik@ozlabs.ru> wrote:

> On 09/08/16 02:43, Alex Williamson wrote:
> > On Wed,  3 Aug 2016 18:40:55 +1000
> > Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
> >   
> >> This exports helpers which are needed to keep a VFIO container in
> >> memory while there are external users such as KVM.
> >>
> >> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> >> ---
> >>  drivers/vfio/vfio.c                 | 30 ++++++++++++++++++++++++++++++
> >>  drivers/vfio/vfio_iommu_spapr_tce.c | 16 +++++++++++++++-
> >>  include/linux/vfio.h                |  6 ++++++
> >>  3 files changed, 51 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> >> index d1d70e0..baf6a9c 100644
> >> --- a/drivers/vfio/vfio.c
> >> +++ b/drivers/vfio/vfio.c
> >> @@ -1729,6 +1729,36 @@ long vfio_external_check_extension(struct vfio_group *group, unsigned long arg)
> >>  EXPORT_SYMBOL_GPL(vfio_external_check_extension);
> >>  
> >>  /**
> >> + * External user API for containers, exported by symbols to be linked
> >> + * dynamically.
> >> + *
> >> + */
> >> +struct vfio_container *vfio_container_get_ext(struct file *filep)
> >> +{
> >> +	struct vfio_container *container = filep->private_data;
> >> +
> >> +	if (filep->f_op != &vfio_fops)
> >> +		return ERR_PTR(-EINVAL);
> >> +
> >> +	vfio_container_get(container);
> >> +
> >> +	return container;
> >> +}
> >> +EXPORT_SYMBOL_GPL(vfio_container_get_ext);
> >> +
> >> +void vfio_container_put_ext(struct vfio_container *container)
> >> +{
> >> +	vfio_container_put(container);
> >> +}
> >> +EXPORT_SYMBOL_GPL(vfio_container_put_ext);
> >> +
> >> +void *vfio_container_get_iommu_data_ext(struct vfio_container *container)
> >> +{
> >> +	return container->iommu_data;
> >> +}
> >> +EXPORT_SYMBOL_GPL(vfio_container_get_iommu_data_ext);
> >> +
> >> +/**
> >>   * Sub-module support
> >>   */
> >>  /*
> >> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> >> index 3594ad3..fceea3d 100644
> >> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
> >> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> >> @@ -1331,6 +1331,21 @@ const struct vfio_iommu_driver_ops tce_iommu_driver_ops = {
> >>  	.detach_group	= tce_iommu_detach_group,
> >>  };
> >>  
> >> +struct iommu_table *vfio_container_spapr_tce_table_get_ext(void *iommu_data,
> >> +		u64 offset)
> >> +{
> >> +	struct tce_container *container = iommu_data;
> >> +	struct iommu_table *tbl = NULL;
> >> +
> >> +	if (tce_iommu_find_table(container, offset, &tbl) < 0)
> >> +		return NULL;
> >> +
> >> +	iommu_table_get(tbl);
> >> +
> >> +	return tbl;
> >> +}
> >> +EXPORT_SYMBOL_GPL(vfio_container_spapr_tce_table_get_ext);
> >> +
> >>  static int __init tce_iommu_init(void)
> >>  {
> >>  	return vfio_register_iommu_driver(&tce_iommu_driver_ops);
> >> @@ -1348,4 +1363,3 @@ MODULE_VERSION(DRIVER_VERSION);
> >>  MODULE_LICENSE("GPL v2");
> >>  MODULE_AUTHOR(DRIVER_AUTHOR);
> >>  MODULE_DESCRIPTION(DRIVER_DESC);
> >> -
> >> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> >> index 0ecae0b..1c2138a 100644
> >> --- a/include/linux/vfio.h
> >> +++ b/include/linux/vfio.h
> >> @@ -91,6 +91,12 @@ extern void vfio_group_put_external_user(struct vfio_group *group);
> >>  extern int vfio_external_user_iommu_id(struct vfio_group *group);
> >>  extern long vfio_external_check_extension(struct vfio_group *group,
> >>  					  unsigned long arg);
> >> +extern struct vfio_container *vfio_container_get_ext(struct file *filep);
> >> +extern void vfio_container_put_ext(struct vfio_container *container);
> >> +extern void *vfio_container_get_iommu_data_ext(
> >> +		struct vfio_container *container);
> >> +extern struct iommu_table *vfio_container_spapr_tce_table_get_ext(
> >> +		void *iommu_data, u64 offset);
> >>  
> >>  /*
> >>   * Sub-module helpers  
> > 
> > 
> > I think you need to take a closer look of the lifecycle of a container,
> > having a reference means the container itself won't go away, but only
> > having a group set within that container holds the actual IOMMU
> > references.  container->iommu_data is going to be NULL once the
> > groups are lost.  Thanks,  
> 
> 
> Container owns the iommu tables and this is what I care about here, groups
> attached or not - this is handled separately via IOMMU group list in a
> specific iommu_table struct, these groups get detached from iommu_table
> when they are removed from a container.

The container doesn't own anything, the container is privileged by the
groups being attached to it.  When groups are closed, they detach from
the container and once the container group list is empty the iommu
backend is released and iommu_data is NULL.  A container reference
doesn't give you what you're looking for.  It implies nothing about the
iommu backend.