Claude review: drm/panthor: Avoid potential UAF due to memory reclaim

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

Patch Review

**Correctness: Good.** The fix correctly ensures that new VA mappings on an already-evicted vm_bo are still invalidated by the shrinker. The original code:

```c
-		/* Skip already evicted GPU mappings. */
-		if (vm_bo->evicted)
-			continue;
```

...was too aggressive — it skipped not just the `drm_gpuvm_bo_evict()` call, but the entire VA walk below it. After the fix, only the `drm_gpuvm_bo_evict()` call is conditionally skipped:

```c
+		if (!vm_bo->evicted)
+			drm_gpuvm_bo_evict(vm_bo, true);
 		drm_gpuvm_bo_for_each_va(va, vm_bo) {
```

**Minor comment issue.** The new comment states:

```c
+		/* ...we don't call drm_gpuvm_bo_evict() again because this would
+		 * mess up with the internal gpuvm lists...
```

This is technically inaccurate. Looking at the underlying `__drm_gpuvm_bo_list_add()` in `drm_gpuvm.c:871`:

```c
static void
__drm_gpuvm_bo_list_add(struct drm_gpuvm *gpuvm, spinlock_t *lock,
			struct list_head *entry, struct list_head *list)
{
	cond_spin_lock(lock, !!lock);
	if (list_empty(entry))
		list_add_tail(entry, list);
	cond_spin_unlock(lock, !!lock);
}
```

The `list_empty()` guard already prevents double-insertion — calling `drm_gpuvm_bo_evict(vm_bo, true)` a second time would be a harmless no-op (evicted is already `true`, and the list add is guarded). The real reason to skip the call is that it's *redundant*, not that it would corrupt lists. Consider rewording to something like: "we skip the redundant drm_gpuvm_bo_evict() call since the vm_bo is already on the evict list."

This is purely a comment accuracy issue — the code behavior is correct either way.

**Locking:** The `mutex_trylock(&vm->op_lock)` path and the `drm_gpuvm_bo_for_each_va` loop are unchanged and remain correct relative to the pre-existing code.

**Fixes tag and attribution look correct.**

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