vgsp: newbind holds are residual-only and short (r237 T2 3 s GP_GET delay)stallfree

r237-2: T2's GR channel carried T1's residual put=115; my 3 s empty-decode
hold delayed the host's GP_GET during the residual walk, and the guest
unwound at binding+3.46 s (zeroed PROMOTE_CTX, then full FREE) - exactly
when the host finally consumed the residual. The guest's ctx-init
patience is ~3 s, so the hold must never delay the walk that long.

- New SVC_GR_NEWBIND_HOLD_MS 1200u and per-channel
  wd_newbind_hold_until: the hold windows (empty-decode and unmapped
  entry) now apply only while it is fresh (<1.2 s; the rebuild lands in
  ~0.8 s) and only when put == get (residual context, no producer work
  pending). Any pending producer work is walked without delay, so
  GP_GET always advances promptly.
- wd_newbind_until (3 s) still governs retry eligibility; the opdef
  drop, chanswitch log, pending-map/rebuild path are unchanged.
  make kernel green.

1 files changed, 22 insertions, 4 deletions

diff --git a/kernel/gsp_sema_service.c b/kernel/gsp_sema_service.c
index 6e37b2f..0520c4f 100644
--- a/kernel/gsp_sema_service.c
+++ b/kernel/gsp_sema_service.c
@@ -425,6 +425,9 @@ struct svc_channel {
 				 * must reconcile the binding before the walk
 				 * (drop dead opdef slots whose since predates
 				 * the binding; log the transition) */
+	unsigned long wd_newbind_hold_until;	/* short hold window inside
+				 * wd_newbind_until (residual-only,
+				 * put==get; never delays fresh work) */
 	unsigned long wd_newbind_until;	/* STALLFREE: freshness window of a
 				 * new binding; inside it an
 				 * unmapped/undecoded GR entry is held
@@ -16604,6 +16607,15 @@ static void svc_userd_sweep(struct nv_vgpu_device *vgpu, struct svc_channel *ch,
  * window of extra latency on first contact.
  */
 #define SVC_GR_NEWBIND_MS	3000u
+/*
+ * STALLFREE r237: the HOLD part of the window must be shorter than the
+ * window itself. r237-2: the 3 s hold on T2's residual ring delayed its
+ * GP_GET past the guest's ~3 s ctx-init patience (T2 unwound with a
+ * zeroed PROMOTE_CTX at binding+3.46 s, exactly when the host finally
+ * consumed the residual). The guest needs GP_GET to advance promptly;
+ * the rebuild lands in ~0.8 s, so 1.2 s is enough for one attempt.
+ */
+#define SVC_GR_NEWBIND_HOLD_MS	1200u
 
 static void svc_gr_stale_wedge_check(struct nv_vgpu_device *vgpu,
 				     struct svc_channel *ch, u32 put, u32 get)
@@ -17195,6 +17207,8 @@ static void svc_pump_channels(struct nv_vgpu_device *vgpu)
 			svc_opdef_drop_channel(vgpu, ch->h_object, jiffies);
 			ch->wd_newbind_until = jiffies +
 				msecs_to_jiffies(SVC_GR_NEWBIND_MS);
+			ch->wd_newbind_hold_until = jiffies +
+				msecs_to_jiffies(SVC_GR_NEWBIND_HOLD_MS);
 			/*
 			 * Bounded proof (r234 asks): the window was armed for
 			 * THIS binding; if a later stall shows no such line,
@@ -17719,9 +17733,10 @@ static void svc_pump_channels(struct nv_vgpu_device *vgpu)
 							    !entry_replay &&
 							    svc_rel_count == rel_n_iter &&
 							    svc_gr_qmd_seen == 0 &&
-							    ch->wd_newbind_until &&
+							    put == get &&
+							    ch->wd_newbind_hold_until &&
 							    time_before(jiffies,
-									ch->wd_newbind_until)) {
+									ch->wd_newbind_hold_until)) {
 								if (!ch->defer_since)
 									ch->defer_since =
 										jiffies;
@@ -18805,9 +18820,10 @@ static void svc_pump_channels(struct nv_vgpu_device *vgpu)
 							 * the rebuild caught up).
 							 */
 							if (!ch->engine_type &&
-							    ch->wd_newbind_until &&
+							    put == get &&
+							    ch->wd_newbind_hold_until &&
 							    time_before(jiffies,
-									ch->wd_newbind_until)) {
+									ch->wd_newbind_hold_until)) {
 								svc.rebuild_now = true;
 								if (svc.gr_pending_map < 16) {
 									svc.gr_pending_map++;
@@ -19045,6 +19061,8 @@ static void svc_pump_channels(struct nv_vgpu_device *vgpu)
 				svc.chan[k].wd_nocap_put = ch->wd_nocap_put;
 				svc.chan[k].wd_chanswitch = ch->wd_chanswitch;
 				svc.chan[k].wd_newbind_until = ch->wd_newbind_until;
+				svc.chan[k].wd_newbind_hold_until =
+					ch->wd_newbind_hold_until;
 				svc.chan[k].pushpg_va = ch->pushpg_va;
 				svc.chan[k].pushpg_n = ch->pushpg_n;
 				svc.chan[k].content_max = ch->content_max;