# session 77 (r683/r684) — vkCreateDevice PASSES: the 0x7E event validation and the readiness-word completion

## The two-part unblock

1. **r682 fix validated** (`e3c1cdc5`, loaded on r683/r684): the
   nvkms/Vulkan path allocates its completion event as
   NV01_EVENT_KERNEL_CALLBACK_EX (class 0x7E); the emulation now
   registers it alongside 0x79. Live proof (r683, sema_dbg=1):

       GSP_RM_ALLOC class=0x7e paramsSize=24 hClient=0xc1e00011
           hParent=0xcaf00001 hObject=0xcaf00003
       event registered hEvent=0xcaf00003 hSrc=0x0
           notifyIndex=1006632972 (off 8, slot 13)
           params=1100e0c1000000007e0000000c00003c0000000000000000
       EVPOST all ev[13] cl=0xc1e00011 ev=0xcaf00003 nidx=0x3c00000c rc=0

   (notifyIndex 0x3c00000c = subdevice 0x3c, index 0xc =
   NV2080_NOTIFIERS_GRAPHICS). The guest consumes the records
   (`guest_read == our_write` in the rmstate dump), but the guest's
   event dispatch does NOT write the event's notification word — the
   residual delivery gap.

2. **The completion word found and driven (the actual unblock)**. The
   main-thread vkCreateDevice wait (eglcore 0xdceb80, session 76) reads
   a u32 readiness word: `should-wait = (word != 1)`; the word lives at
   `+0x80` of a **16 KB rw-s /dev/nvidiactl mapping** (the event
   notification buffer; holder chain sub -> obj2 -> holder, resolved
   live by t79.py). The host can write it directly in the guest RAM
   file:

       PA = pagemap PFN << 12  (+0x80);  file offset = PA - 0x80000000
       (above-4G RAM; below-4G would be PA itself per the cycle's
       guest-RAM registration: gpa 0x0/0x100000000 -> off 0x0/0x80000000)

   Writing 1 flipped the wait and **vkCreateDevice returned success**
   (`VKDEVICE ok family=0`) — reproduced three times:
   * r683: manual write after a t79 probe;
   * r684: nudger (all 16 KB mapping words) + slotfill restart;
   * r684d: probe -> single-word write (the reliable recipe).

## The reliable recipe (per run)

1. r682+ module; `sema_dbg=1 gsp_rm_ev_log=300` optional.
2. Launch `vk_frame` + `slotfill2.sh` (EGL completion-slot fills; the
   slots re-arm, so re-run slotfill if the client is stuck in the
   sched_yield spin before the word-wait).
3. Wait for the main thread in `do_poll` (the word-wait).
4. `t79.py` (gdb) -> `WAIT word=0x...`; guest pagemap -> PFN -> PA;
   host write `01 00 00 00` at `PA-0x80000000`.
5. `VKDEVICE ok` follows within ~10 s. The client then proceeds to
   image/memory/pipeline setup; its next wait is NOT the same word
   (the word stays 1) — next session: probe the follow-on state
   (attach fails while the client spins in the post-device phase;
   use the /proc-only checks + a longer observation window).

## Cautions learned

* Writing ALL 16 KB mapping words (the multi-page nudger) can trip the
  -4 give-up path (an RM error flag word gets written): restrict nudges
  to the single probed word.
* Attaching gdb to the client while it is in the tight post-device spin
  can hang the attach (leave a `timeout`-wrapped gdb, then kill that
  gdb by PID and `kill -CONT` the client — the pending SIGSTOP from a
  dead tracer otherwise wedges it).
* zsh truncates 64-bit hex literals in `$(( ))`: compute PFN/PA in
  python, not zsh.

## Tools

* `t79.py` — resolves the wait chain (sub -> obj2 -> holder -> word VA)
  and prints the client's nvidiactl rw-s mapping sizes.
* `guest_words.sh` — prints VA/PA of the +0x80 word for every 16 KB
  nvidiactl mapping (pagemap; run in the guest as root).
* `nudge.sh` — host-side loop: poll guest_words.sh and write 1 to any
  zero word (multi-page variant; prefer the single-word recipe).

## ADDENDUM (r685, session 78) — POST-DEVICE WAIT IDENTIFIED: the NvOgl (GL ucode) engine init; push windows now READABLE (resolver6)

* The post-device spin is the **GL module bring-up**: the main thread's
  A8-layer retry loop (eglcore 0xa85d24) works on a work item whose
  embedded name is ASCII **"NvOgl_m0"** (+0xf04: "NvOgl_m40"); the D6
  submit layer (0xd624e0) ORs **0x200000** into its pending word (the
  same engine-pending bit SESSION 75/76 watched on E+0x150), then the
  A8 loop yields via the B284B0 spin helper (sched_yield) waiting for
  the GL ucode init to complete on the GR engine.
* **The push windows ARE now readable** (first time): the resolver6
  recipe (window-record pair {push_va,0x20000}+{ring_va,0x40000} ->
  same-page 0x20000 memdesc PA -> `sema_map_add`) injected
  `0x4480000 -> 0x120cfb000` (content `2001c00d 70000000 2001c00d
  68000000` = the 2-method semaphore-like push) and `0x4ca0000 ->
  0x12e51e000` (the 1432-byte GR init stream: SET_OBJECT 0xc5c0/0xc5b5,
  `0x200121ed`, `0x200120a9`, bulk methods, tail `2001c00d
  70/68`). The service now decodes the streams (`sema-push ... tail=0dc0
  012000000070...`) where SESSION 73-74 saw "unread".
  CAUTION: the resolver injects every candidate; a zero-page candidate
  injected last replaces the good mapping for that VA (re-inject the
  good page after the scan).
* **Remaining gate**: the service still reports `have_rel=0` for every
  GR push (the CE-shaped release matcher) and — decisively — the
  GR-forward machinery is NOT engaging: `drain held=4 starved=149
  forwarded=0 ... gr_nocap=4`. The GL ucode init work is never
  forwarded/executed, so the completion (and the 0x200000 bit clear)
  never arrives. Next: the GR forward/capture path for these channels
  (operand capture + release decode for the GR shape), then the client
  proceeds to VKFRAME.