Claude review: drm/amdgpu: add SVM attr prefetch/force-trigger functionality

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

Patch Review

**Overall:** Small and focused. The one-shot prefetch semantics are well-motivated.

**Issue: `preferred_loc` changes no longer trigger `LOCATION_CHANGE`:**
```c
-	if (prev_attrs->preferred_loc != new_attrs->preferred_loc ||
-	    prev_attrs->prefetch_loc != new_attrs->prefetch_loc)
+	if (prev_attrs->prefetch_loc != new_attrs->prefetch_loc)
 		trigger |= AMDGPU_SVM_ATTR_TRIGGER_LOCATION_CHANGE;
```
This means changing `preferred_loc` alone will never trigger migration. In patch 5, `amdgpu_svm_range_apply_attr_change()` only acts on `AMDGPU_SVM_ATTR_TRIGGER_LOCATION_CHANGE` for migration. So if userspace sets a new `preferred_loc` without also issuing a prefetch, the new location preference won't take effect until the next fault or restore event. Is this intentional? The commit message doesn't explain this tradeoff.

**Good:** The `force_trigger` change from `bool` to `uint32_t` bitmask is the right approach — it allows composing multiple trigger reasons.

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Generated by Claude Code Patch Reviewer