vgsp: guest GR forwarding backend and capture (gsp_phys_gr_forward, default off)gr-forwarding

Add a default-off guest GR (compute) forwarding path so a guest CUDA
launch submitted on its GR channel can be executed by the physical GR
engine on the ladder channel, with fail-closed fallback to the host CUDA
bridge and the unchanged software release path.

- New module parameter gsp_phys_gr_forward (default 0) and accessor.
- New GR execution gate: boot_stage.rmcall_gr_exec_ok, latched only after
  a real GR submission logs REAL GR SEM OK; the backend refuses while it
  is unset.
- Sema capture: a completed 64-word inline QMD on a trusted, non-replay
  GR decode becomes an svc_gr_cand (push identity, decoded release0,
  parameter/program/pointer fields, up to 8 captured inline-write
  records); the CUDA bridge stays authoritative while the parameter is
  off and is reached in order forward -> bridge -> software release.
- Backend: gsp_phys_backend_guest_gr_submit() maps pages at their own
  guest VAs through fresh Tier-1 small-PT pages/PDE installs or relocates
  inline-captured pages to ladder shadow pages (Tier 2), builds
  SET_OBJECT + the inline-QMD method run + REPORT_SEMAPHORE on the
  compute subchannel, reuses the shared GPFIFO/USERD/doorbell publish
  tail (extracted from the CE submit path, CE bytes unchanged) and polls
  the QMD release and/or module semaphore, draining the epoch-gated
  fault queue on timeout.
- Sema wiring: GR requests reuse the INFLIGHT/hold/deferral machinery so
  the guest channel release applies only on the submit's success/failure
  edge; hold shims preserve the channel engine type.
- Counters and a work_gr state line plus a stats accessor.
- Bounds are fixed: 16 pages, 8 inline records, 64 QMD words; every
  pointer/size checked, pool exhaustion and stale mappings fail closed.
- New ABI layouts pinned with static_asserts.

Compile-only change: no device test performed.

1 files changed, 12 insertions, 0 deletions

diff --git a/kernel/gsp_phys_gpu.h b/kernel/gsp_phys_gpu.h
index 74e3103..b204961 100644
--- a/kernel/gsp_phys_gpu.h
+++ b/kernel/gsp_phys_gpu.h
@@ -92,6 +92,18 @@ bool gsp_phys_srv_ctxbuf_value(void);
 bool gsp_phys_work_forward_enabled(void);
 
 /*
+ * True when the gsp_phys_gr_forward module parameter is set (default 0: guest
+ * GR (compute) launches stay on the existing host CUDA bridge / software
+ * path). When set, the sema service captures a completed guest inline QMD and
+ * the booter submits it as real work on the ladder's physical GR channel,
+ * but only after boot_stage.rmcall_gr_exec_ok proved a real GR submission at
+ * boot (gsp_phys_backend_gr_ready() enforces the gate). Every forward
+ * refusal/failure falls back to the CUDA bridge (when enabled) and then the
+ * unchanged software release path. One-line rollback: gsp_phys_gr_forward=0.
+ */
+bool gsp_phys_gr_forward_enabled(void);
+
+/*
  * True when the gsp_phys_guest_mem module parameter is set (default 0: the
  * debugfs rm-call ladder stays entirely on module-owned buffers, exactly as
  * before). When set, ladder triggers 6 (W2G) and 7 (G2H) may point the real