From 3031f72e6408a894c05d3cf1679e4bb7d074d989 Mon Sep 17 00:00:00 2001
From: Arthur Hanson Rasmusson <arthur@vgpu.io>
Date: Tue, 29 Sep 2026 13:18:00 -0400
Subject: guest-diag: resolve pushbuffer from uvpbf kprobe pointer
 (deterministic)

---
 tools/guest-diag/semfix_watch.py | 45 ++++++++++++++++++++++++++++++++++------
 1 file changed, 39 insertions(+), 6 deletions(-)

(limited to 'tools')

diff --git a/tools/guest-diag/semfix_watch.py b/tools/guest-diag/semfix_watch.py
index 0de5cad..8fd534d 100644
--- a/tools/guest-diag/semfix_watch.py
+++ b/tools/guest-diag/semfix_watch.py
@@ -87,16 +87,34 @@ def is_gpu(v):
     return v and GPU_VA_LO <= v < GPU_VA_HI
 
 
-def guest_sems():
-    """Kernel pointers of tracking semaphores the client is spinning on."""
+def guest_trace():
+    """(sem kptrs, pushbuffer kptrs) from the trace ring, then clear it."""
     cmd = ("sudo sh -c 'echo > /sys/kernel/tracing/trace; sleep 2; "
-           "grep uvmt /sys/kernel/tracing/trace | tail -4'")
+           "grep -E \"uvmt|uvpb\" /sys/kernel/tracing/trace | tail -8'")
     try:
         out = subprocess.run([VMEXEC, "exec", cmd], capture_output=True,
                              text=True, timeout=90).stdout
     except Exception:
-        return set()
-    return {int(m, 16) for m in re.findall(r"sem=0x([0-9a-fA-F]+)", out)}
+        return set(), set()
+    sems = {int(m, 16) for m in re.findall(r"sem=0x([0-9a-fA-F]+)", out)}
+    pbs = {int(m, 16) for m in re.findall(r"pb=0x([0-9a-fA-F]+)", out)}
+    return sems, pbs
+
+
+def resolve_pb_ptr(q, pb):
+    """pushbuffer pointer -> rm_mem -> vas[] -> (gpu_vas, cpu, gpa)."""
+    mem = q.read64(pb + 8)
+    if not mem or not is_kern(mem[0]):
+        return [], None, None
+    vas = q.read64(mem[0] + 0x10, 16)
+    gpu_vas = [v for v in vas if PUSHBUF_VA_LO <= v < PUSHBUF_VA_HI]
+    cpu = next((v for v in vas if is_kern(v)), None)
+    if not gpu_vas or not cpu:
+        return [], None, None
+    gpa = q.gva2gpa(cpu)
+    if not gpa:
+        return [], None, None
+    return gpu_vas, cpu, gpa
 
 
 def pin(va, pa):
@@ -201,10 +219,25 @@ def main():
     interval = float(sys.argv[1]) if len(sys.argv) > 1 else 3.0
     q = Qmp(QMP_SOCK)
     seen = set()
+    seen_pb = set()
     pb_done = False
     print("semfix: watching (interval %.1fs)" % interval, flush=True)
     while True:
-        for sem in guest_sems() - seen:
+        sems, pbs = guest_trace()
+        if not pb_done:
+            for pb in pbs - seen_pb:
+                seen_pb.add(pb)
+                try:
+                    gpu_vas, cpu, gpa = resolve_pb_ptr(q, pb)
+                except Exception as e:
+                    print("semfix: pb=0x%x resolve failed: %s" % (pb, e), flush=True)
+                    continue
+                if gpu_vas:
+                    pin_pushbuffer(q, gpu_vas, cpu, gpa)
+                    pb_done = True
+                    break
+                print("semfix: pb=0x%x no pushbuffer rm_mem (retry)" % pb, flush=True)
+        for sem in sems - seen:
             try:
                 pairs = resolve_sem_pool(q, sem)
             except Exception as e:
-- 
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