sema-svc: bounded diagnostics for GR counter writes; scanner guarantees counter-page delta

- rel-apply/publish now log the first 32/48 outcomes (written, skipped with
  current value, no slot, read failure) so the live counter page can be
  matched against host writes.
- guest pin scanner logs the counter page's pagemap state each loop and adds
  it to the delta set explicitly, so the page is pinned the moment it is
  mapped even if the window scan misses it.

1 files changed, 22 insertions, 2 deletions

diff --git a/tools/guest-diag/guest_pin_stream.py b/tools/guest-diag/guest_pin_stream.py
index 8d0b34d..717a05d 100644
--- a/tools/guest-diag/guest_pin_stream.py
+++ b/tools/guest-diag/guest_pin_stream.py
@@ -141,6 +141,26 @@ def main():
             time.sleep(INTERVAL)
             continue
         dt = time.time() - t0
+        # Diagnostic: the GR completion-counter page is the one page the
+        # client's context-init wait polls; log its pagemap entry every loop
+        # so a scan blind spot is visible in the guest log.
+        cpm = None
+        try:
+            fdp = os.open('/proc/%d/pagemap' % pid, os.O_RDONLY)
+            os.lseek(fdp, (0x20400fec0 // 4096) * 8, 0)
+            cpm = int.from_bytes(os.read(fdp, 8), 'little')
+            os.close(fdp)
+        except OSError:
+            cpm = None
+        diag = ('cpm=%s' % ('present' if (cpm or 0) >> 63 & 1 else 'absent')
+                if cpm is not None else 'cpm=ERR')
+        # Guaranteed fast path for the GR completion-counter page: if the
+        # window scan misses it (observed once), add it explicitly so the host
+        # can register the slots before the client's first wait.
+        if cpm is not None and (cpm >> 63) & 1:
+            cpa = (cpm & ((1 << 55) - 1)) << 12
+            if cpa and (not PAMAX or cpa < PAMAX):
+                cur[0x20400f000] = cpa
         new = [(va, pa) for va, pa in cur.items() if seen.get(va) != pa]
         seen = cur
         lines = []
@@ -152,9 +172,9 @@ def main():
             last_log = now
             try:
                 with open('/tmp/guest_pin_stream.log', 'a') as f:
-                    f.write('%s pid=%s present=%d new=%d sem=%d scan=%.3fs\n'
+                    f.write('%s pid=%s present=%d new=%d sem=%d scan=%.3fs %s\n'
                             % (time.strftime('%T'), pid, len(cur), len(new),
-                               len(seen_sems), dt))
+                               len(seen_sems), dt, diag))
             except OSError:
                 pass
         if not new and not lines: