cover-letter: Introduce fwctl subystem

fwctl is a new subsystem intended to bring some common rules and order to
the growing pattern of exposing a secure FW interface directly to
userspace. Unlike existing places like RDMA/DRM/VFIO/uacce that are
exposing a device for datapath operations fwctl is focused on debugging,
configuration and provisioning of the device. It will not have the
necessary features like interrupt delivery to support a datapath.

This concept is similar to the long standing practice in the "HW" RAID
space of having a device specific misc device to manager the RAID
controller FW. fwctl generalizes this notion of a companion debug and
management interface that goes along with a dataplane implemented in an
appropriate subsystem.

The need for this has reached a critical point as many users are moving to
run lockdown enabled kernels. Several existing devices have had long
standing tooling for management that relied on /sys/../resource0 or PCI
config space access which is not permitted in lockdown. A major point of
fwctl is to define and document the rules that a device must follow to
expose a lockdown compatible RPC.

Based on some discussion fwctl splits the RPCs into four categories

	FWCTL_RPC_CONFIGURATION
	FWCTL_RPC_DEBUG_READ_ONLY
	FWCTL_RPC_DEBUG_WRITE
	FWCTL_RPC_DEBUG_WRITE_FULL

Where the latter two trigger a new TAINT_FWCTL, and the final one requires
CAP_SYS_RAWIO - excluding it from lockdown. The device driver and its FW
would be responsible to restrict RPCs to the requested security scope,
while the core code handles the tainting and CAP checks.

For details see the final patch which introduces the documentation.

This series incorporates a version of the mlx5ctl interface previously
proposed:
  https://lore.kernel.org/r/[email protected]/

For this series the memory registration mechanism was removed, but I
expect it will come back.

It also includes the FWCL driver series from David:
  https://lore.kernel.org/all/[email protected]/


This is still waiting a 3rd fwctl driver and the CXL side to finish some
of its development. The github has the necessary CXL precursor patches.

There have been two LWN articles written discussing various aspects of
this proposal:

 https://lwn.net/Articles/955001/
 https://lwn.net/Articles/969383/

And a really giant ksummit thread:

 https://lore.kernel.org/ksummit/[email protected]/

Several have expressed general support for this concept:

 Broadcom Networking - https://lore.kernel.org/r/Zf2n02q0GevGdS-Z@C02YVCJELVCG
 Christoph Hellwig - https://lore.kernel.org/r/[email protected]/
 Daniel Vetter - https://lore.kernel.org/r/[email protected]
 Enfabrica - https://lore.kernel.org/r/[email protected]/
 NVIDIA Networking
 Oded Gabbay/Habana - https://lore.kernel.org/r/ZrMl1bkPP-3G9B4N@T14sgabbay.
 Oracle Linux - https://lore.kernel.org/r/6lakj6lxlxhdgrewodvj3xh6sxn3d36t5dab6najzyti2navx3@wrge7cyfk6nq
 SuSE/Hannes - https://lore.kernel.org/r/[email protected]

Work is ongoing for a robust multi-device open source userspace, currently
the mlx5ctl_user that was posted by Saeed has been updated to use fwctl.

  https://github.com/saeedtx/mlx5ctl.git
  https://github.com/jgunthorpe/mlx5ctl.git

This is on github: https://github.com/jgunthorpe/linux/commits/fwctl

v3:
 - Rebase to v6.11-rc4
 - Add a squashed version of David's CXL series as the 2nd driver
 - Add missing includes
 - Improve comments based on feedback
 - Use the kdoc format that puts the member docs inside the struct
 - Rewrite fwctl_alloc_device() to be clearer
 - Incorporate all remarks for the documentation
v2: https://lore.kernel.org/r/[email protected]
 - Rebase to v6.10-rc5
 - Minor style changes
 - Follow the style consensus for the guard stuff
 - Documentation grammer/spelling
 - Add missed length output for mlx5 get_info
 - Add two more missed MLX5 CMD's
 - Collect tags
v1: https://lore.kernel.org/r/[email protected]

Cc: Andy Gospodarek <[email protected]>
Cc: Aron Silverton <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Itay Avraham <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Jiri Pirko <[email protected]>
Cc: Leon Romanovsky <[email protected]>
Cc: Leonid Bloch <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>