virtio_input: fix DMA alignment for evts

virtio_input: fix DMA alignment for evts

On non-cache-coherent platforms, when a structure contains a buffer
used for DMA alongside fields that the CPU writes to, cacheline sharing
can cause data corruption.

The evts array is used for DMA_FROM_DEVICE operations via
virtqueue_add_inbuf(). The adjacent lock and ready fields are written
by the CPU during normal operation. If these share cachelines with evts,
CPU writes can corrupt DMA data.

Add __dma_from_device_group_begin()/end() annotations to ensure evts is
isolated in its own cachelines.

Message-ID: <cd328233198a76618809bb5cd9a6ddcaa603a8a1.1767601130.git.mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>