r510 keep the page-directory discovery attempts for coherent evidence: a large mixed-space map no longer burns them

r508/r509 witness: 'page directory discovery: not found (base=0x0 ap=ram
cands=39621 best=0/8)' during the very first client - eight RAM walks
spent on a stride subsample of the boot-scoped map, which holds pairs from
several VA spaces and (per the code's own comment) no single directory
reproduces. By the time the push-buffer pairs - the strongest samples -
formed, the attempts budget was gone; every later client's high argument
pointers stayed unresolvable and the boot ended in the held-launch class.
Only a small map (one session's own pairs) still falls back; a larger one
waits for the pairs and keeps the attempts.

1 files changed, 17 insertions, 2 deletions

diff --git a/kernel/gsp_sema_service.c b/kernel/gsp_sema_service.c
index 6fa1813..bc21e95 100644
--- a/kernel/gsp_sema_service.c
+++ b/kernel/gsp_sema_service.c
@@ -2258,8 +2258,23 @@ static void svc_pd_discover(struct nv_vgpu_device *vgpu)
 	}
 	if (n < SVC_PD_MIN_HITS) {
 		n = 0;
-		if (svc.map_n < SVC_PD_SAMPLES)
-			return;	/* no evidence yet: retry when pairs appear */
+		/*
+		 * r510: a LARGE map is a mixed set of VA spaces cached over
+		 * the whole guest boot (the comment above already names the
+		 * consequence: no single directory reproduces a mixed set), so
+		 * scanning with its stride subsample burns the attempts budget
+		 * on evidence that cannot succeed - and by the time the
+		 * push-buffer pairs (the strongest samples) exist, the budget
+		 * is spent (r508/r509 witness: 'not found (base=0x0 ap=ram
+		 * cands=39621 best=0/8)' during the first client, eight RAM
+		 * walks consumed, every later client's high argument pointers
+		 * unresolvable - the terminal class). Only a SMALL map, which
+		 * is one session's own pairs, still falls back; otherwise wait
+		 * for the push-buffer pairs and keep the attempts.
+		 */
+		if (svc.map_n > (u32)(SVC_PD_SAMPLES * 2) ||
+		    svc.map_n < SVC_PD_SAMPLES)
+			return;	/* no coherent evidence yet: retry later */
 		step = svc.map_n / SVC_PD_SAMPLES;
 		for (i = 0; i < SVC_PD_SAMPLES; i++) {
 			sva[i] = svc.map[i * step].gpu_page;