nitro_enclaves: Handle out-of-band PCI device events

nitro_enclaves: Handle out-of-band PCI device events

In addition to the replies sent by the Nitro Enclaves PCI device in
response to command requests, out-of-band enclave events can happen e.g.
an enclave crashes. In this case, the Nitro Enclaves driver needs to be
aware of the event and notify the corresponding user space process that
abstracts the enclave.

Register an MSI-X interrupt vector to be used for this kind of
out-of-band events. The interrupt notifies that the state of an enclave
changed and the driver logic scans the state of each running enclave to
identify for which this notification is intended.

Create an workqueue to handle the out-of-band events. Notify user space
enclave process that is using a polling mechanism on the enclave fd.

Changelog

v9 -> v10

* Update commit message to include the changelog before the SoB tag(s).

v8 -> v9

* Use the reference to the pdev directly from the ne_pci_dev instead of
  the one from the enclave data structure.

v7 -> v8

* No changes.

v6 -> v7

* No changes.

v5 -> v6

* Update documentation to kernel-doc format.

v4 -> v5

* Remove sanity checks for situations that shouldn't happen, only if
  buggy system or broken logic at all.

v3 -> v4

* Use dev_err instead of custom NE log pattern.
* Return IRQ_NONE when interrupts are not handled.

v2 -> v3

* Remove the WARN_ON calls.
* Update static calls sanity checks.
* Remove "ratelimited" from the logs that are not in the ioctl call
  paths.

v1 -> v2

* Add log pattern for NE.
* Update goto labels to match their purpose.

Reviewed-by: Alexander Graf <graf@amazon.com>
Signed-off-by: Alexandru-Catalin Vasile <lexnv@amazon.com>
Signed-off-by: Andra Paraschiv <andraprs@amazon.com>
Link: https://lore.kernel.org/r/20200921121732.44291-7-andraprs@amazon.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>