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

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

Patch Review

**Build-breaking bug.** The `xe_vm_add_fault_entry_pf` function references `pf->consumer.fault_type_level` and uses `FIELD_GET` with `XE_PAGEFAULT_TYPE_MASK` and `XE_PAGEFAULT_LEVEL_MASK`:

> +	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),

The `struct xe_pagefault` has separate `fault_type` and `fault_level` fields (both `u8`), not a combined `fault_type_level` field. Neither `XE_PAGEFAULT_TYPE_MASK` nor `XE_PAGEFAULT_LEVEL_MASK` is defined anywhere in the tree. This code will not compile. It appears to be based on an older version of the `xe_pagefault` struct. The fix is straightforward:

```c
e->fault_type = pf->consumer.fault_type;
e->fault_level = pf->consumer.fault_level;
```

**Comma instead of semicolon.** Those same two lines end with commas instead of semicolons. Due to C's comma operator, the two assignment expressions and the subsequent `list_add_tail` call end up chained into a single expression-statement. While this would execute correctly (all three expressions evaluate left to right), it is clearly unintentional and should use semicolons.

**Allocation under potential pressure.** The function calls `kzalloc(sizeof(*e), GFP_KERNEL)` from within `xe_pagefault_queue_work`, a workqueue handler that processes page faults. If the system is under memory pressure (which is exactly when page faults are likely), this allocation could sleep and delay fault processing. Worth considering whether `GFP_NOWAIT` or a pre-allocated pool would be more appropriate here, though this is a design consideration rather than a bug.

**Race window on VM close.** `xe_pagefault_save_to_vm` does `xe_vm_get(vm)` under `xe->usm.lock`, then calls `xe_vm_add_fault_entry_pf`, then `xe_vm_put`. Meanwhile, `xe_vm_close_and_put` calls `xe_vm_clear_fault_entries` after releasing `xe->usm.lock`. The per-fault spinlock (`vm->faults.lock`) protects the list operations, so no corruption occurs, but a fault could be added to a VM that is in the process of being torn down, only to be immediately freed by `xe_vm_clear_fault_entries`. This is harmless but worth noting.

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