The issue is related to a functional regression in the Linux kernel's swiotlb component, which causes double-allocation of slots due to broken alignment handling. This can lead to buffer corruption and/or a hang when using vsock in a virtual machine with a restricted DMA SWIOTLB pool. The problem occurs because swiotlb alloc() expects a page-aligned allocation but returns a pointer to the 'struct page' corresponding to the allocation, resulting in double-allocation of the first half of the 4KiB page. The issue is resolved by treating the allocation alignment separately from any additional alignment requirements from the device.