From 8898bd00b7c2e6385ceb7238f29d3672308b949a Mon Sep 17 00:00:00 2001
From: Arthur Hanson Rasmusson <arthur@vgpu.io>
Date: Tue, 27 Oct 2026 06:36:00 -0400
Subject: 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.
---
 kernel/gsp_rm_emulation.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

(limited to 'kernel/gsp_rm_emulation.c')

diff --git a/kernel/gsp_rm_emulation.c b/kernel/gsp_rm_emulation.c
index d6412c3..fc08b9d 100644
--- a/kernel/gsp_rm_emulation.c
+++ b/kernel/gsp_rm_emulation.c
@@ -3052,8 +3052,21 @@ static bool gsp_rm_is_channel_class(u32 class_id)
 	case 0x906f:	/* MAXWELL_CHANNEL_GPFIFO_A */
 	case 0xa06f:	/* KEPLER_CHANNEL_GPFIFO_A */
 	case 0xb06f:	/* PASCAL_CHANNEL_GPFIFO_A */
-	case 0xc06f:	/* VOLTA_CHANNEL_GPFIFO_A */
+	case 0xc06f:	/* VOLTA_CHANNEL_GPFIFO_A (PRE-TURING NAME) */
+	case 0xc36f:	/* VOLTA_CHANNEL_GPFIFO_A */
+		/*
+		 * r828: the RC watchdog's channel allocates 0xc36f on this
+		 * device (the driver's gpfifoMapping loop picks the first
+		 * class the gpu reports supported) - without it in this set
+		 * the channel never reaches the progress service, its class2d
+		 * notifier cycle (SET_NOTIFY_A/B + NOTIFY) never executes and
+		 * the guest's krcWatchdog declares the GPU locked after its
+		 * 7 s timeout as soon as robust channels are in play.
+		 */
 	case 0xc46f:	/* TURING_CHANNEL_GPFIFO_A */
+	case 0xc56f:	/* AMPERE_CHANNEL_GPFIFO_A */
+	case 0xc86f:	/* HOPPER_CHANNEL_GPFIFO_A */
+	case 0xc96f:	/* BLACKWELL_CHANNEL_GPFIFO_A */
 		return true;
 	default:
 		return false;
@@ -3075,8 +3088,18 @@ static void gsp_rm_register_channel(struct gsp_emu_context *ctx, u32 h_object,
 {
 	struct sema_channel_desc desc;
 
-	if (params_size < GSPRM_CHAN_NOTIFIER_MEM + 8)
+	if (params_size < GSPRM_CHAN_NOTIFIER_MEM + 8) {
+		/*
+		 * r828 diag: a channel-class alloc whose params are shorter
+		 * than the notifier field is not registered, silently. The
+		 * RC watchdog channel (hObject 0x31415900) never appeared in
+		 * the sema table; name every such skip with its size so the
+		 * shape question is answered by a log, not inference.
+		 */
+		pr_info("vgsp-rm: channel alloc hObject=0x%x params_size=%u too short (< %u); NOT registered\n",
+			h_object, params_size, GSPRM_CHAN_NOTIFIER_MEM + 8);
 		return;
+	}
 
 	memset(&desc, 0, sizeof(desc));
 	desc.vgpu = ctx->vgpu;
-- 
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