Claude review: drm/amdkfd: Add user_range_info infrastructure to kgd_mem

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

Patch Review

**Overview:** Adds per-range metadata structures.

**Issues:**

1. **Race Condition - Critical:**
```c
+struct user_range_info {
+	uint64_t start;
+	uint64_t size;
+	struct hmm_range *range;
+	bool valid;				/* Flag: true if pages are valid, false if invalidated */
+	struct interval_tree_node it_node;
+};
```
The `valid` flag is accessed without proper locking documentation. This flag is:
- Set in `init_user_pages_batch()` under `process_info->lock`
- Cleared in `discard_invalid_ranges()` under `process_info->notifier_lock`
- Read in validation paths potentially without locks

This creates a race window where `valid` could be stale.

2. **Type Inconsistency:**
Uses both `uint64_t` and `__u64`. Kernel code should prefer fixed-width types like `u64`.

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Generated by Claude Code Patch Reviewer