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

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

Patch Review

1. **Comma instead of semicolon (bug):**

```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 of these lines end with `,` (comma operator) instead of `;`. While this compiles and works because the comma operator evaluates both sides, it's definitely a bug/typo. Both should end with `;`.

2. **`access_type` stored without masking:**

```c
e->access_type = pf->consumer.access_type;
```

As noted in patch 1, `pf->consumer.access_type` has `XE_PAGEFAULT_ACCESS_PREFETCH` packed into bit 7. This will leak the prefetch bit into the stored access_type, which then gets exposed to userspace. It should be masked:

```c
e->access_type = pf->consumer.access_type & XE_PAGEFAULT_ACCESS_TYPE_MASK;
```

3. **Allocation under potential memory pressure:** `xe_pagefault_save_to_vm` calls `kzalloc(GFP_KERNEL)` in the page fault handler path. The fault handling path may already be under memory pressure (the fault may have been triggered by reclaim). Consider using `GFP_NOWAIT` or at least `GFP_KERNEL | __GFP_NOWARN`.

4. **Typo in comment:** "asociated" should be "associated" in the comment in `xe_pagefault_save_to_vm`.

5. **Fault list never cleared by userspace:** The faults accumulate up to 50 and then are silently discarded. There's no mechanism for userspace to clear the fault list after reading it. This means after 50 faults are hit, no new faults will ever be recorded. This seems like a significant design limitation — userspace can read the same stale faults forever and never see new ones.

6. **`xe_vm_clear_fault_entries` only called on VM close:** The fault list is only cleaned up on `xe_vm_close_and_put`. If userspace never closes the VM, these 50 allocations persist forever (which is fine, it's bounded, but the list is never useful after filling up).

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