vgsp: service the guest RC watchdog channel (Volta GPFIFO class + class2d notifier ack)

The guest kernel's krcWatchdog posts a notifier cycle on its own channel
(object 0x31415900) every second and declares 'GPU is probably locked'
when the zeroed notification never comes back within 7 s. Observed as
the sustained-GL-load wedge: once a GL client (GZDOOM) enabled robust
channels the errors started and Xorg eventually stalled on screen
readback.

- rm: register the Volta GPFIFO class 0xc36f (plus the later
  generations) as a channel class. The watchdog's channel allocates
  0xc36f on this device - the driver picks the first class the gpu
  reports supported - and without it the channel never reached the
  progress service. It now registers and latches (put visible, entries
  walked).
- sema: decode the class2d notifier cycle on subchannel 3
  (SET_NOTIFY_A/B name the notifier VA, NOTIFY WRITE_ONLY writes the
  zeroed NvNotification) and author the write, like svc_notify_complete
  does for the work-submit token. Proven live: 'sema-notify2d: va=...
  zeroed (RC watchdog acked)'.
- sema: also ack on every pass that sees the channel's put != get, so
  the ack does not depend on the ring reads (its VA is known from the
  first decode); idempotent.
- sema: never consume a zero-length/zero-VA GPFIFO entry as empty work.
  Two bogus zero entries consumed through a mis-resolved ring page
  pushed the watchdog userd's GPGet past the driver's own GPPut and
  every later userd probe then read get>put, permanently rejecting the
  channel's real userd. Hold such entries (bounded, per-channel
  counter persists through the pass snapshot).
- sema: a registered userd value that is a real guest PA (the
  watchdog's own block) outranks the ring+0x2000 convention guess the
  ring auto-pin applies for the CUDA GR layout.
- rm: log channel-class allocs whose params are too short for
  registration instead of skipping silently.

Remaining (next): under heavy GL traffic the watchdog ring's
translation can go stale for stretches (content-scanned map answering
where a pin used to), which starves the ack; pin the push/notifier
pages when the first real decode delivers them. The frame capture
(xshm_pub -> XShmGetImage) still stalls while that starvation is
active.

0 files changed, 0 insertions, 0 deletions