vgsp-sema r626: sema_no_shadow - A/B knob to disable the VA shadow lane (copy-dst + fill fallbacks hold instead); isolates the lane as a variable for the fatal corruption class (nvidia channel structs overwritten with PTE-like patterns -> panic in kchannelGetGfid_IMPL via nvGpuOpsStopChannel; r613c/r616/r623c)

1 files changed, 15 insertions, 0 deletions

diff --git a/kernel/gsp_sema_service.c b/kernel/gsp_sema_service.c
index e76cb7a..0e8474f 100644
--- a/kernel/gsp_sema_service.c
+++ b/kernel/gsp_sema_service.c
@@ -2696,8 +2696,23 @@ static bool svc_vas_has(u64 va)
  * 100 TiB). Explicit sources (GRCE inline writes, the bridge's output write)
  * shadow any VA because their target is device memory by construction.
  */
+bool gsp_sema_no_shadow;	/* r626 A/B: disable the shadow lane */
+module_param_named(sema_no_shadow, gsp_sema_no_shadow, bool, 0644);
+MODULE_PARM_DESC(sema_no_shadow,
+	"Disable the VA shadow lane (copy-dst and fill fallbacks) for an A/B boot; unresolved device VAs hold instead (default 0)");
+
 static bool svc_vas_can_shadow(u64 va)
 {
+	/*
+	 * r626 A/B: with the knob set, every shadow fallback is refused and
+	 * the caller takes its -ENOENT/hold path. The r613c/r616/r623c
+	 * corruption class (nvidia channel structures overwritten with
+	 * PTE-like 0x444../0x4456.. patterns, fatal panic in
+	 * kchannelGetGfid_IMPL via nvGpuOpsStopChannel) follows the
+	 * shadow-lane era; this knob isolates the lane as a variable.
+	 */
+	if (gsp_sema_no_shadow)
+		return false;
 	return va >= SVC_VAS_FLOOR;
 }