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Re: [Qemu-block] [PATCH 2/2] virtio-scsi/virtio-blk: Disable poll handle
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-block] [PATCH 2/2] virtio-scsi/virtio-blk: Disable poll handlers when stopping vq handler |
Date: |
Thu, 13 Sep 2018 11:11:57 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 |
On 13/09/2018 08:03, Fam Zheng wrote:
> On Wed, 09/12 14:42, Paolo Bonzini wrote:
>> 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?
>
> I'm not sure if it is a bug or not. I think what happens is the device is left
> enabled by Seabios, and then reset by kernel.
That makes sense, though I'm not sure why QEMU needs to process a
request long after SeaBIOS has left control to Linux. Maybe it's just
that the messages should not go on QEMU stderr, and rather trace-point
should be enough.
Paolo
- [Qemu-block] [PATCH 1/2] virtio: Return true from virtio_queue_empty if broken, (continued)
- [Qemu-block] [PATCH 1/2] virtio: Return true from virtio_queue_empty if broken, Fam Zheng, 2018/09/10
- [Qemu-block] [PATCH 2/2] virtio-scsi/virtio-blk: Disable poll handlers when stopping vq handler, Fam Zheng, 2018/09/10
- Re: [Qemu-block] [PATCH 2/2] virtio-scsi/virtio-blk: Disable poll handlers when stopping vq handler, Paolo Bonzini, 2018/09/11
- Re: [Qemu-block] [PATCH 2/2] virtio-scsi/virtio-blk: Disable poll handlers when stopping vq handler, Fam Zheng, 2018/09/11
- Re: [Qemu-block] [PATCH 2/2] virtio-scsi/virtio-blk: Disable poll handlers when stopping vq handler, Paolo Bonzini, 2018/09/11
- Re: [Qemu-block] [PATCH 2/2] virtio-scsi/virtio-blk: Disable poll handlers when stopping vq handler, Fam Zheng, 2018/09/11
- Re: [Qemu-block] [PATCH 2/2] virtio-scsi/virtio-blk: Disable poll handlers when stopping vq handler, Paolo Bonzini, 2018/09/12
- Re: [Qemu-block] [PATCH 2/2] virtio-scsi/virtio-blk: Disable poll handlers when stopping vq handler, Fam Zheng, 2018/09/12
- Re: [Qemu-block] [PATCH 2/2] virtio-scsi/virtio-blk: Disable poll handlers when stopping vq handler, Paolo Bonzini, 2018/09/12
- Re: [Qemu-block] [PATCH 2/2] virtio-scsi/virtio-blk: Disable poll handlers when stopping vq handler, Fam Zheng, 2018/09/13
- Re: [Qemu-block] [PATCH 2/2] virtio-scsi/virtio-blk: Disable poll handlers when stopping vq handler,
Paolo Bonzini <=
- Re: [Qemu-block] [PATCH 2/2] virtio-scsi/virtio-blk: Disable poll handlers when stopping vq handler, Paolo Bonzini, 2018/09/13
- Re: [Qemu-block] [PATCH 2/2] virtio-scsi/virtio-blk: Disable poll handlers when stopping vq handler, Alex Williamson, 2018/09/13
- Re: [Qemu-block] [PATCH 2/2] virtio-scsi/virtio-blk: Disable poll handlers when stopping vq handler, Peter Xu, 2018/09/13