kernel: Fix GSP emulation shadow binding, eventfd wiring, RPC livelocks + docs suite + repo reorg

CRITICAL FIXES (guest driver bring-up):
- gsp_emulation.c: emulation engine bound to the WRONG BAR0 - it polled the
  host physical BAR0 (bars[0].vaddr ioremap) for the doorbell and read RPCs
  from a local dma_alloc_wc buffer, while the guest writes land in the
  vzalloc'd bar0_shadow. The RPC path could never work; PBA writes even
  corrupted the host GPU's physical BAR0+0x3000. gsp_emu_init now binds
  exclusively to bar0_shadow (doorbell/mailbox/PBA aliases;
  shared_mem_dma==0 marks the alias so cleanup never dma_free's it).
- main.c SET_IRQS: DATA_EVENTFD eventfds were DISCARDED ('TODO' + kfree) -
  the guest never received MSI-X completions. Full wiring now:
  eventfd_ctx_fdget per vector, fd -1 clears, dev_close releases refs.
  gsp_emu_inject_completion_interrupt looks up vgpu->irqs[0].trigger LIVE
  (init-time copy was permanently NULL since QEMU wires after gsp_emu_init).
- gsp_rpc_client.c: BAR_TRAP/MIGRATE in emulation mode called
  gsp_rpc_submit_raw which rings the SAME doorbell the thread polls -
  self-triggered RPC livelock + multi-second stalls. Now fail fast with
  -ENOTSUPP + pr_warn_ratelimited (guest BAR access is direct MMIO).

MORE FIXES:
- main.c: nv_vgpu_config_write returned SIZE_MAX (while(count--) wrap) and
  was dead code while the VFIO write handler did unfiltered byte copies
  (guest could rewrite vendor ID/BARs). Return fixed; VFIO write handler
  now routes through the per-register filter.
- kernel/Makefile: M=$(PWD) used the env var which is stale when invoked
  via the top-level make (pointed at repo root -> kbuild silently built
  NOTHING; explains every 'stale .ko' incident). Now M=$(CURDIR).
- Warnings sweep: header prototypes for mdev/type functions, format casts
  in gsp_comm.c DRY-RUN logs, unused variable.

ROBUSTNESS (harness/tooling):
- vgpu_vm.py: run had no timeout (start could block forever);
  guest_shell recv could block forever on a wedged guest. Both now bounded;
  guest_shell pre-flights guest-ping and reports wedge diagnostics.
- stack_manager.sh: qemu/qemu-debug now launch via the vgpu_vm.py harness
  (workflow rule: never raw QEMU).

REPO REORGANIZATION:
- driver/ (legacy guest-side gsp-vgpu.ko) moved to legacy-driver-guest/
  (reference only, not built; README explains). 3 legacy un-buildable test
  files moved to legacy-driver-guest/kernel-tests/. Top-level Makefile
  cleaned of the dead DRIVER_DIR reference.

DOCUMENTATION SUITE (new):
- docs/GSP_EMULATION_ARCHITECTURE.md - emulator deep-dive: shadow BAR0
  model, doorbell protocol, dispatch table, MSI-X path, lifecycle, memory-
  model caveats
- docs/DEBUGGING.md - QEMU GDB stub workflow, serial console, QMP NMI,
  failure taxonomy, full bring-up validation checklist, EPT-livelock case
  study, version-matrix discipline
- docs/ONBOARDING.md - repo tour, coding standards (incl. virt_to_phys /
  dma_addr_t / get-put rules), first build & test
- docs/VERSION_UPGRADE.md - end-to-end new-driver-version procedure
  (firmware fetch, Ghidra analysis, configs, signatures, validation)
- docs/PERFORMANCE.md - bare-metal A/B methodology + targets
- README.md doc index; STATE.md refreshed; DEVELOPMENT_WORKFLOW.md corrected
  (load order: open-iov-vfio BEFORE nvidia; stock-driver blacklist note)

1 files changed, 34 insertions, 6 deletions

diff --git a/kernel/gsp_rpc_client.c b/kernel/gsp_rpc_client.c
index ae45513..93c1876 100644
--- a/kernel/gsp_rpc_client.c
+++ b/kernel/gsp_rpc_client.c
@@ -375,8 +375,8 @@ int gsp_rpc_unpin(struct gsp_client *client, u64 handle, u64 offset, u64 size)
 
 /* BAR Trap Emulation */
 int gsp_rpc_bar_trap(struct gsp_client *client,
-                      u64 bar_addr, u32 access_type, u32 size,
-                      u64 value, u32 bar_num, u64 *ret_value)
+                       u64 bar_addr, u32 access_type, u32 size,
+                       u64 value, u32 bar_num, u64 *ret_value)
 {
     struct gsp_bar_trap_req req = {0};
     struct gsp_bar_trap_rsp rsp = {0};
@@ -384,6 +384,17 @@ int gsp_rpc_bar_trap(struct gsp_client *client,
     u32 seq = gsp_next_seq(client);
     int ret;
 
+    /* In emulation mode there is no real firmware to submit to, and
+     * submit_raw would ring the very doorbell the emulation thread polls
+     * (self-triggered RPC livelock + timeout stall). Guest BAR access is
+     * synchronous MMIO via the shadow mapping and never needs this RPC.
+     * Real shadow-register handlers are TODO; fail fast and loudly. */
+    if (gsp_rpc_emulation_is_enabled()) {
+        pr_warn_ratelimited("gsp_rpc_bar_trap: not supported in emulation mode (bar=%u addr=0x%llx)\n",
+                            bar_num, bar_addr);
+        return -ENOTSUPP;
+    }
+
     req.bar_addr = bar_addr;
     req.access_type = access_type;
     req.size = size;
@@ -413,9 +424,19 @@ int gsp_rpc_migrate_save(struct gsp_client *client,
     struct gsp_migrate_req req = {0};
     struct gsp_migrate_rsp rsp = {0};
     struct gsp_rpc_response response = {0};
-    u32 seq = gsp_next_seq(client);
+    u32 seq;
     int ret;
 
+    /* Emulation mode: no real firmware; submit_raw would ring the doorbell
+     * the emulation thread polls (self-triggered livelock + 30s stall).
+     * Live migration over the emulated vGPU is not yet implemented;
+     * see kernel/migration.c for the 4-phase host-side protocol work. */
+    if (gsp_rpc_emulation_is_enabled()) {
+        pr_warn_ratelimited("gsp_rpc_migrate_save: not supported in emulation mode\n");
+        return -ENOTSUPP;
+    }
+
+    seq = gsp_next_seq(client);
     req.src_gpu_id = src_gpu_id;
     req.dst_gpu_id = dst_gpu_id;
     req.memory_bitmap = memory_bitmap;
@@ -444,9 +465,16 @@ int gsp_rpc_migrate_restore(struct gsp_client *client,
 {
     struct gsp_migrate_req req = {0};
     struct gsp_rpc_response response = {0};
-    u32 seq = gsp_next_seq(client);
+    u32 seq;
     int ret;
 
+    /* Emulation mode: no real firmware; see gsp_rpc_migrate_save note. */
+    if (gsp_rpc_emulation_is_enabled()) {
+        pr_warn_ratelimited("gsp_rpc_migrate_restore: not supported in emulation mode\n");
+        return -ENOTSUPP;
+    }
+
+    seq = gsp_next_seq(client);
     req.src_gpu_id = src_gpu_id;
     req.dst_gpu_id = dst_gpu_id;
     req.memory_bitmap = memory_bitmap;
@@ -777,7 +805,7 @@ int gsp_rpc_schedule(struct gsp_client *client,
     u32 seq = gsp_next_seq(client);
     int ret;
     
-    if (gsp_emulation_enabled) {
+    if (gsp_rpc_emulation_is_enabled()) {
         struct gsp_sched_work *sched = kzalloc(sizeof(*sched), GFP_KERNEL);
         if (!sched)
             return -ENOMEM;
@@ -827,7 +855,7 @@ int gsp_rpc_yield(struct gsp_client *client)
     u32 seq = gsp_next_seq(client);
     int ret;
     
-    if (gsp_emulation_enabled) {
+    if (gsp_rpc_emulation_is_enabled()) {
         /* In emulation, yield is a no-op success */
         return 0;
     }