vgsp-sema: resolve the CE push buffer from the kernel chain (second-client stall)

The second CUDA client's GPFIFO entries in the CE push-buffer window
(0x120000000) had no injected pin: that window is never mapped into the
client's pagemap, so the scanner's window scan cannot see it, and its
only supplier - the one-shot uvbp kprobe event - is raced by two trace
clears (the scanner's pid-switch clear and semfix's trace-tail clear).
When the event loses the race the entry reads fall back to the ~250 ms
content rescue, which is the second-client stall and the same
resolution-miss class as the ISSUE-0001 lottery.

The guest scanner now walks channel->pool->manager->pushbuffer->rm_mem
in kernel memory with kcore and pins the push-buffer pages directly (no
trace event to lose), and the trace reader's dedup marks reset on a
client switch so a reused kptr cannot suppress the new client's #pb.

Boot evidence (r112): rescue reject ipin=0 for va_page=0x120023000,
rescue scans 175 ms - 1 s each, want incrementing to 39. Smoke test of
this fix on the stalled VM: 478 pin runs (~7955 pages) streamed within
seconds, first va=0x120000000 -> pa=0x108090000. A bounded kernel log
now prints the first CE push-buffer pins of each session.

0 files changed, 0 insertions, 0 deletions