On 11/06/2019 19:13, Jacob Pan wrote: >>>> +/** >>>> + * ioasid_find - Find IOASID data >>>> + * @set: the IOASID set >>>> + * @ioasid: the IOASID to find >>>> + * @getter: function to call on the found object >>>> + * >>>> + * The optional getter function allows to take a reference to the >>>> found object >>>> + * under the rcu lock. The function can also check if the object >>>> is still valid: >>>> + * if @getter returns false, then the object is invalid and NULL >>>> is returned. >>>> + * >>>> + * If the IOASID has been allocated for this set, return the >>>> private pointer >>>> + * passed to ioasid_alloc. Private data can be NULL if not set. >>>> Return an error >>>> + * if the IOASID is not found or does not belong to the set. >>> >>> Perhaps should make it clear that @set can be null. >> >> Indeed. But I'm not sure allowing @set to be NULL is such a good idea, >> because the data type associated to an ioasid depends on its set. For >> example SVA will put an mm_struct in there, and auxiliary domains use >> some structure private to the IOMMU domain. >> > I am not sure we need to count on @set to decipher data type. Whoever > does the allocation and owns the IOASID should knows its own data type. > My thought was that @set is only used to group IDs, permission check > etc. > >> Jacob, could me make @set mandatory, or do you see a use for a global >> search? If @set is NULL, then callers can check if the return pointer >> is NULL, but will run into trouble if they try to dereference it. >> > A global search use case can be for PRQ. IOMMU driver gets a IOASID > (first interrupt then retrieve from a queue), it has no idea which > @set it belongs to. But the data types are the same for all IOASIDs > used by the IOMMU. They aren't when we use a generic SVA handler. Following a call to iommu_sva_bind_device(), iommu-sva.c allocates an IOASID and store an mm_struct. If auxiliary domains are also enabled for the device, following a call to iommu_aux_attach_device() the IOMMU driver allocates an IOASID and stores some private object. Now for example the IOMMU driver receives a PPR and calls ioasid_find() with @set = NULL. ioasid_find() may return either an mm_struct or a private object, and the driver cannot know which it is so the returned value is unusable. Thanks, Jean
