On 12/09/2018 13:50, Fam Zheng wrote: >> I think it's okay if it is invoked. The sequence is first you stop the >> vq, then you drain the BlockBackends, then you switch AioContext. All >> that matters is the outcome when virtio_scsi_dataplane_stop returns. > Yes, but together with vIOMMU, it also effectively leads to a virtio_error(), > which is not clean. QEMU stderr when this call happens (with patch 1 but not > this patch): > > 2018-09-12T11:48:10.193023Z qemu-system-x86_64: vtd_iommu_translate: detected > translation failure (dev=02:00:00, iova=0x0) > 2018-09-12T11:48:10.193044Z qemu-system-x86_64: New fault is not recorded due > to compression of faults > 2018-09-12T11:48:10.193061Z qemu-system-x86_64: virtio: zero sized buffers > are not allowed
But with iothread, virtio_scsi_dataplane_stop runs in another thread than the iothread; in that case you still have a race where the iothread can process the vq before aio_disable_external and print the error. IIUC the guest has cleared the IOMMU page tables _before_ clearing the DRIVER_OK bit in the status field. Could this be a guest bug? Paolo
