From 7dfcf8dae7ebbc06430897997b55999428bdb372 Mon Sep 17 00:00:00 2001
From: Arthur Hanson Rasmusson <arthur@vgpu.io>
Date: Sun, 25 Oct 2026 18:43:30 -0400
Subject: vgsp-sema: per-client unconditional push-read attempt witness -
 sema-rdw (h/va/len/rc/winning-src, budget 400/client, reset in
 svc_session_flush) at the pump read site plus the r707x src out-param
 (svc_read_last_src) inside svc_read_va_push_ex; also per-client reset of the
 sema-pushfail budget. r713: the run reproduced VKDEVICE+flips+VKFAIL but the
 witness rows scrolled out of the 2 KB dmesg ring before capture - the next
 run must read dmesg immediately after the first skips (or raise the ring
 buffer)

---
 kernel/gsp_sema_service.c | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/kernel/gsp_sema_service.c b/kernel/gsp_sema_service.c
index 76fcdf5..c9f5969 100644
--- a/kernel/gsp_sema_service.c
+++ b/kernel/gsp_sema_service.c
@@ -3020,6 +3020,11 @@ struct svc_ipin_alt {
 static struct svc_ipin_alt svc_ipin_alt[SVC_IPIN_ALT_SLOTS];
 static u64 svc_pushalt_hits;	/* push reads served by a displaced pair */
 static u32 svc_pushalt_log;
+/* r707x: per-client push-read attempt witness (pump read site). */
+static u32 svc_rdw_log;
+static u8 svc_read_last_src;
+/* r707d: bounded push-read failure witness (see svc_read_va_push_ex). */
+static u32 svc_pushfail_log;
 
 static int svc_ipin_alt_lookup(u64 va, u64 *pa, int *ap)
 {
@@ -12691,6 +12696,9 @@ static void svc_gr_defer_reset(void);
 
 static void svc_session_flush(void)
 {
+	/* r707x: per-client witness budgets. */
+	svc_pushfail_log = 0;
+	svc_rdw_log = 0;
 	unsigned long flags;
 	u32 i;
 
@@ -14067,9 +14075,11 @@ static int svc_read_va_push_ex(struct nv_vgpu_device *vgpu,
 			 */
 			if (src == 3 && first && !memchr_inv(p, 0, chunk))
 				continue;
+			svc_read_last_src = (u8)src;
 			done = true;
 		}
 		if (!done) {
+			svc_read_last_src = 0xff;
 			if (svc_pushfail_log < 96) {
 				u64 ipa = 0, apa = 0;
 				int iap = 0, aap = 0;
@@ -24414,9 +24424,21 @@ static void svc_pump_channels(struct nv_vgpu_device *vgpu)
 
 				if (pb) {
 					int rescue_rc;
-					bool unreadable =
-						svc_read_va_push(vgpu, ch, va,
-								 pb, len) != 0;
+					int rd_rc;
+					bool unreadable;
+
+					svc_read_last_src = 0xff;
+					rd_rc = svc_read_va_push(vgpu, ch, va,
+								 pb, len);
+					unreadable = rd_rc != 0;
+					if (gsp_sema_dbg && svc_rdw_log < 400 &&
+					    !ch->engine_type) {
+						svc_rdw_log++;
+						pr_info("sema-rdw: h=0x%x va=0x%llx len=%u rc=%d src=%u\n",
+							ch->h_object, va, len,
+							rd_rc,
+							(unsigned)svc_read_last_src);
+					}
 					bool injected = false;
 					bool allow_ops = (ch->engine_type != 0);
 
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