From c332445746b8a8ef46869c3b47e165c375bb1f8d Mon Sep 17 00:00:00 2001
From: Arthur Hanson Rasmusson <arthur@vgpu.io>
Date: Tue, 3 Nov 2026 17:43:19 -0500
Subject: vgsp-sph: C4 - capture scratch 0x19 (CB selector, mthd 0x3464) + seed
 STATE 0xD19 emission (param sema_mme_state_d19 > captured, 3d-reloc,
 fail-closed) - the d28-forced slow path reads an unseeded d19 and faults the
 consumer at VA 0 (HUBCLIENT_PD); +129/-1

---
 kernel/gsp_sema_service.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 54 insertions(+), 1 deletion(-)

(limited to 'kernel/gsp_sema_service.c')

diff --git a/kernel/gsp_sema_service.c b/kernel/gsp_sema_service.c
index 4546bb0..08f2309 100644
--- a/kernel/gsp_sema_service.c
+++ b/kernel/gsp_sema_service.c
@@ -14768,12 +14768,35 @@ bool gsp_sema_mme_scratch18_get(u32 *val)
 	return svc_scratch18_seen;
 }
 
+/*
+ * SESSION 153-CONTINUED-115: companion capture for the bug2548370 slow-path
+ * selector. STATE 0xD19 / shadow scratch 0x19 (method 0x3464 =
+ * SET_MME_SHADOW_SCRATCH(0x19)) is the constant-buffer selector B/C
+ * (address>>8) the macro's in-band update emits from once the fast path is
+ * refused (d28 forced); when the replay context never receives the client's
+ * once-per-channel write the selector resolves to 0 and the consumer fetches
+ * constants from address 0 - the same failure mode documented for 0x18. The
+ * value is stored exactly as pushed; the GR launch builder can fall back to
+ * sema_mme_state_d19 when this never fires.
+ */
+static u32 svc_scratch19_val;
+static bool svc_scratch19_seen;
+static u32 svc_scratch19_log;
+
+bool gsp_sema_mme_scratch19_get(u32 *val)
+{
+	if (svc_scratch19_seen && val)
+		*val = READ_ONCE(svc_scratch19_val);
+	return svc_scratch19_seen;
+}
+
 static void svc_scratch18_watch(const u8 *buf, u32 len, u64 push_va,
 				u32 h_object)
 {
 	u32 off = 0;
 
-	if (svc_scratch18_seen && svc_scratch18_log >= 24u)
+	if (svc_scratch18_seen && svc_scratch18_log >= 24u &&
+	    svc_scratch19_seen && svc_scratch19_log >= 24u)
 		return;
 	while (off + 4u <= len) {
 		u32 hdr, op, cnt, addr;
@@ -14801,6 +14824,23 @@ static void svc_scratch18_watch(const u8 *buf, u32 len, u64 push_va,
 				off += 4u + cnt * 4u;
 				continue;
 			}
+			if (addr == 0x3464u) {
+				u32 val;
+
+				memcpy(&val, buf + off + 4, 4);
+				if (!svc_scratch19_seen) {
+					svc_scratch19_seen = true;
+					WRITE_ONCE(svc_scratch19_val, val);
+				}
+				if (svc_scratch19_log < 24u) {
+					svc_scratch19_log++;
+					pr_info("sema-scratch19: h=0x%x va=0x%llx off=0x%x op=%u cnt=%u val=0x%08x (SET_MME_SHADOW_SCRATCH(0x19); CB selector B/C address>>8)\n",
+						h_object, push_va, off, op, cnt,
+						val);
+				}
+				off += 4u + cnt * 4u;
+				continue;
+			}
 			off += 4u + cnt * 4u;
 			continue;
 		}
@@ -14817,6 +14857,19 @@ static void svc_scratch18_watch(const u8 *buf, u32 len, u64 push_va,
 					h_object, push_va, off, val);
 			}
 		}
+		if (op == 4u && addr == 0x3464u) {
+			u32 val = (hdr >> 16) & 0x1fffu;
+
+			if (!svc_scratch19_seen) {
+				svc_scratch19_seen = true;
+				WRITE_ONCE(svc_scratch19_val, val);
+			}
+			if (svc_scratch19_log < 24u) {
+				svc_scratch19_log++;
+				pr_info("sema-scratch19: h=0x%x va=0x%llx off=0x%x op=4 immd val=0x%08x (SET_MME_SHADOW_SCRATCH(0x19); CB selector B/C address>>8)\n",
+					h_object, push_va, off, val);
+			}
+		}
 		off += 4u;
 	}
 }
-- 
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