Claude review: Re: [PATCH] drm/appletbdrm: Use kvzalloc for big allocations

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

Patch Review

**NAK — vmalloc memory cannot be used as a USB DMA transfer buffer.**

The allocation site:
```c
-	appletbdrm_state->request = kzalloc(request_size, GFP_KERNEL);
+	appletbdrm_state->request = kvzalloc(request_size, GFP_KERNEL);
```

This buffer is subsequently passed to USB bulk transfer at `appletbdrm.c:449`:
```c
ret = appletbdrm_send_request(adev, &request->header, request_size);
```

Which calls `usb_bulk_msg()` at line 160:
```c
ret = usb_bulk_msg(udev, usb_sndbulkpipe(udev, adev->out_ep),
		   request, size, &actual_size, APPLETBDRM_BULK_MSG_TIMEOUT);
```

The USB HCD layer DMA-maps this buffer via `dma_map_single()` (`drivers/usb/core/hcd.c:1488`), and the DMA subsystem explicitly rejects vmalloc addresses (`include/linux/dma-mapping.h:513-515`). When `kvzalloc` falls back to vmalloc under memory pressure — the exact scenario this patch targets — the USB transfer will fail.

The free-side change is correct in isolation (matching `kvzalloc` with `kvfree`), but is moot given the allocation change is wrong:
```c
-	kfree(appletbdrm_state->request);
+	kvfree(appletbdrm_state->request);
```

**Suggestion:** Replace `kvzalloc` with `kzalloc` using `__GFP_RETRY_MAYFAIL`:
```c
appletbdrm_state->request = kzalloc(request_size, GFP_KERNEL | __GFP_RETRY_MAYFAIL);
```

This tells the page allocator to try harder (compacting memory, reclaiming pages) before giving up, while keeping the allocation physically contiguous and safe for DMA. No change needed on the free side since `kfree` remains correct.

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Generated by Claude Code Patch Reviewer