Claude review: drm/xe/xe_vm: Add per VM fault info

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**Comma operator bug.** In `xe_vm_add_fault_entry_pf()`:
```c
e->fault_type = FIELD_GET(XE_PAGEFAULT_TYPE_MASK,
              pf->consumer.fault_type_level),
e->fault_level = FIELD_GET(XE_PAGEFAULT_LEVEL_MASK,
               pf->consumer.fault_type_level),
```
Both lines end with `,` (comma) instead of `;` (semicolon). While this compiles and works in this specific context (comma operator evaluates left-to-right and the result is discarded by the next statement), it looks like a typo and could confuse readers. Should be semicolons.

**Memory allocation under potential pressure.** `xe_pagefault_save_to_vm()` calls `kzalloc(sizeof(*e), GFP_KERNEL)` from a workqueue context processing page faults. This should be fine since `GFP_KERNEL` is appropriate here, but the allocation is done before checking `MAX_FAULTS_SAVED_PER_VM` — the check happens inside the spinlock. Moving the length check before the allocation would avoid wasted allocations:

```c
// Could check vm->faults.len first with the lock, then allocate
```

Though the current approach (allocate then check under lock) does avoid holding the lock during allocation, which is the right tradeoff. The wasted allocation on a full list is minor.

**`access_type` stored raw.** `e->access_type = pf->consumer.access_type` stores the raw value including the prefetch bit. The conversion in patch 4 (`xe_to_user_access_type`) then masks it. This means the internal representation differs from the uAPI representation. This works but is fragile — it would be cleaner to mask at storage time in `xe_vm_add_fault_entry_pf()`.

**Prefetch faults are saved.** `xe_pagefault_save_to_vm()` is called for all failed faults, but back in `xe_pagefault_queue_work()`, prefetch faults that fail are treated as benign (only a debug log). Saving prefetch faults to the VM fault list and exposing them to userspace seems inconsistent with the stated goal of only reporting meaningful failed faults. Consider filtering out prefetch faults in `xe_pagefault_save_to_vm()`.

---
Generated by Claude Code Patch Reviewer