The ice driver stores VF structures in a simple array which is allocated
once at the time of VF creation. The VF structures are then accessed
from the array by their VF ID. The ID must be between 0 and the number
of allocated VFs.

Multiple threads can access this table:

 * .ndo operations such as .ndo_get_vf_cfg or .ndo_set_vf_trust
 * interrupts, such as due to messages from the VF using the virtchnl
   communication
 * processing such as device reset
 * commands to add or remove VFs

The current implementation does not keep track of when all threads are
done operating on a VF and can potentially result in use-after-free
issues caused by one thread accessing a VF structure after it has been
released when removing VFs. Some of these are prevented with various
state flags and checks.

In addition, this structure is quite static and does not support a
planned future where virtualization can be more dynamic. As we begin to
look at supporting Scalable IOV with the ice driver (as opposed to just
supporting Single Root IOV), this structure is not sufficient.

In the future, VFs will be able to be added and removed individually and
dynamically.

To allow for this, and to better protect against a whole class of
use-after-free bugs, replace the VF storage with a combination of a hash
table and krefs to reference track all of the accesses to VFs through
the hash table.

A hash table still allows efficient look up of the VF given its ID, but
also allows adding and removing VFs. It does not require contiguous VF
IDs.

The use of krefs allows the cleanup of the VF memory to be delayed until
after all threads have released their reference (by calling ice_put_vf).

To prevent corruption of the hash table, a combination of RCU and the
mutex table_lock are used. Addition and removal from the hash table use
the RCU-aware hash macros. This allows simple read-only look ups that
iterate to locate a single VF can be fast using RCU. Accesses which
modify the hash table, or which can't take RCU because they sleep, will
hold the mutex lock.

By using this design, we have a stronger guarantee that the VF structure
can't be released until after all threads are finished operating on it.
We also pave the way for the more dynamic Scalable IOV implementation in
the future.
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Konrad Jankowski <konrad0.jankowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>