[PATCH v6 07/25] iommufd/access: Add internal APIs for HW queue to use

[Jason Gunthorpe]

On Sat, Jun 14, 2025 at 12:14:32AM -0700, Nicolin Chen wrote:
> Now, access->ops can be NULL, to support an internal use case for the new
> HW queue object. Since an access object in this case will be allocated by
> an inernal iommufd object, the refcount on the ictx should be skipped, so
> as not to deadlock the release of the ictx as it would otherwise wait for
> the release of the access first during the release of the internal object
> that could wait for the release of ictx:
>     ictx --releases--> hw_queue --releases--> access
>       ^                                         |
>       |_________________releases________________v
> 
> Add a set of lightweight internal APIs to unlink access and ictx:
>     ictx --releases--> hw_queue --releases--> access
> 
> Signed-off-by: Nicolin Chen <nicolinc at nvidia.com>
> ---
>  drivers/iommu/iommufd/iommufd_private.h |  8 ++++
>  drivers/iommu/iommufd/device.c          | 59 +++++++++++++++++++++----
>  2 files changed, 58 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
> index 4a375a8c9216..468717d5e5bc 100644
> --- a/drivers/iommu/iommufd/iommufd_private.h
> +++ b/drivers/iommu/iommufd/iommufd_private.h
> @@ -484,6 +484,14 @@ void iopt_remove_access(struct io_pagetable *iopt,
>  			struct iommufd_access *access, u32 iopt_access_list_id);
>  void iommufd_access_destroy_object(struct iommufd_object *obj);
>  
> +/* iommufd_access for internal use */
> +struct iommufd_access *iommufd_access_create_internal(struct iommufd_ctx *ictx);
> +#define iommufd_access_destroy_internal(ictx, access) \
> +	iommufd_object_destroy_user(ictx, &(access)->obj)

Use a static inline please

> +int iommufd_access_attach_internal(struct iommufd_access *access,
> +				   struct iommufd_ioas *ioas);
> +#define iommufd_access_detach_internal(access) iommufd_access_detach(access)


>  struct iommufd_eventq {
>  	struct iommufd_object obj;
>  	struct iommufd_ctx *ictx;
> diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
> index 9293722b9cff..ad33f1e41a24 100644
> --- a/drivers/iommu/iommufd/device.c
> +++ b/drivers/iommu/iommufd/device.c
> @@ -1084,7 +1084,39 @@ void iommufd_access_destroy_object(struct iommufd_object *obj)
>  	if (access->ioas)
>  		WARN_ON(iommufd_access_change_ioas(access, NULL));
>  	mutex_unlock(&access->ioas_lock);
> -	iommufd_ctx_put(access->ictx);
> +	if (access->ops)
> +		iommufd_ctx_put(access->ictx);

I was hoping we could null the ictx to signal internal? That didn't
work out?

I would at least add a comment here this is filtering internal that
doesn't have ictx. Maybe a little inline 'iommufd_access_is_internal'
is appropriate. We'll be sad down the road if we need ops for
internal.

Jason