Sure. I hit this with a generic vhost-vdpa virtio-blk device when changing the write cache mode.
For virtio-blk, the guest updates virtio_blk_config.wce when switching between write through and write back. Without this patch, QEMU still passes the old s->config buffer to VHOST_VDPA_SET_CONFIG, so the backend does not see the new wce value. I reproduced it with vdpa_sim_blk. After writing wce=1 and then wce=0, the byte corresponding to virtio_blk_config.wce in the buffer passed to VHOST_VDPA_SET_CONFIG remained unchanged without this patch: guest writes wce=1: 0x0020: 00 00 01 00 ... guest writes wce=0: 0x0020: 00 00 01 00 ... With this patch, the same writes are passed down correctly: guest writes wce=1: 0x0020: 01 00 00 00 ... guest writes wce=0: 0x0020: 00 00 00 00 ... So from the guest's perspective the write cache mode change appears to succeed, but the updated value never reaches the vDPA backend because VHOST_VDPA_SET_CONFIG receives stale configuration data.
