Virtualization - Dec 2020 - [PATCH RFC 00/12] vdpa: generalize vdpa simulator and add block device

On 2020/12/18 ??7:38, Stefano Garzarella wrote:
> On Mon, Nov 16, 2020 at 11:37:48AM +0800, Jason Wang wrote:
>>
>> On 2020/11/13 ??9:47, Stefano Garzarella wrote:
>>> Thanks to Max that started this work!
>>> I took his patches, and extended the block simulator a bit.
>>>
>>> This series moves the network device simulator in a new module
>>> (vdpa_sim_net) and leaves the generic functions in the vdpa_sim
core
>>> module, allowing the possibility to add new vDPA device simulators.
>>> Then we added a new vdpa_sim_blk module to simulate a block device.
>>>
>>> I'm not sure about patch 11 ("vringh: allow
vringh_iov_xfer() to skip
>>> bytes when ptr is NULL"), maybe we can add a new functions
instead of
>>> modify vringh_iov_xfer().
>>>
>>> As Max reported, I'm also seeing errors with vdpa_sim_blk
related to
>>> iotlb and vringh when there is high load, these are some of the
error
>>> messages I can see randomly:
>>>
>>> ? vringh: Failed to access avail idx at 00000000e8deb2cc
>>> ? vringh: Failed to read head: idx 6289 address 00000000e1ad1d50
>>> ? vringh: Failed to get flags at 000000006635d7a3
>>>
>>> ? virtio_vdpa vdpa0: vringh_iov_push_iotlb() error: -14 offset: ? 
>>> 0x2840000 len: 0x20000
>>> ? virtio_vdpa vdpa0: vringh_iov_pull_iotlb() error: -14 offset: ? 
>>> 0x58ee000 len: 0x3000
>>>
>>> These errors should all be related to the fact that
iotlb_translate()
>>> fails with -EINVAL, so it seems that we miss some mapping.
>>
>>
>> Is this only reproducible when there's multiple co-current
accessing
>> of IOTLB? If yes, it's probably a hint that some kind of 
>> synchronization is still missed somewhere.
>>
>> It might be useful to log the dma_map/unmp in both virtio_ring and 
>> vringh to see who is missing the map.
>>
>
> Just an update about these issues with vdpa-sim-blk.
> I've been focusing a little bit on these failures over the last few 
> days and have found two issues related to the IOTLB/IOMMU:
>
> 1. Some requests coming from the block layer fills the SG list with 
> multiple buffers that had the same physical address. This happens for 
> example while using 'mkfs', at some points multiple sectors are
zeroed
> so multiple SG elements point to the same physical page that is zeroed.
> Since we are using vhost_iotlb_del_range() in the 
> vdpasim_unmap_page(), this removes all the overlapped ranges. I fixed 
> removing a single map in vdpasim_unmap_page(), but has an alternative 
> we can implement some kind of reference counts.

I think we need to do what hardware do. So using refcount is probably 
not a good ida.

>
> 2. There was a race between dma_map/unmap and the worker thread, since 
> both are accessing the IOMMU. Taking the iommu_lock while using 
> vhost_iotlb_* API in the worker thread fixes the "vringh: Failed to
*"
> issues.
>
> Whit these issues fixed the vdpa-blk simulator seems to work well.
> I'll send the patches next week or after the break.

Good to know this.

Thanks

>
> Thanks,
> Stefano
>

On Mon, Dec 21, 2020 at 11:16:54AM +0800, Jason Wang
wrote:
>
>On 2020/12/18 ??7:38, Stefano Garzarella wrote:
>>On Mon, Nov 16, 2020 at 11:37:48AM +0800, Jason Wang wrote:
>>>
>>>On 2020/11/13 ??9:47, Stefano Garzarella wrote:
>>>>Thanks to Max that started this work!
>>>>I took his patches, and extended the block simulator a bit.
>>>>
>>>>This series moves the network device simulator in a new module
>>>>(vdpa_sim_net) and leaves the generic functions in the vdpa_sim
core
>>>>module, allowing the possibility to add new vDPA device
simulators.
>>>>Then we added a new vdpa_sim_blk module to simulate a block
device.
>>>>
>>>>I'm not sure about patch 11 ("vringh: allow
vringh_iov_xfer() to skip
>>>>bytes when ptr is NULL"), maybe we can add a new functions
instead of
>>>>modify vringh_iov_xfer().
>>>>
>>>>As Max reported, I'm also seeing errors with vdpa_sim_blk
related to
>>>>iotlb and vringh when there is high load, these are some of the
error
>>>>messages I can see randomly:
>>>>
>>>>? vringh: Failed to access avail idx at 00000000e8deb2cc
>>>>? vringh: Failed to read head: idx 6289 address 00000000e1ad1d50
>>>>? vringh: Failed to get flags at 000000006635d7a3
>>>>
>>>>? virtio_vdpa vdpa0: vringh_iov_push_iotlb() error: -14 offset: 
>>>>? 0x2840000 len: 0x20000
>>>>? virtio_vdpa vdpa0: vringh_iov_pull_iotlb() error: -14 offset: 
>>>>? 0x58ee000 len: 0x3000
>>>>
>>>>These errors should all be related to the fact that
iotlb_translate()
>>>>fails with -EINVAL, so it seems that we miss some mapping.
>>>
>>>
>>>Is this only reproducible when there's multiple co-current 
>>>accessing of IOTLB? If yes, it's probably a hint that some kind
of
>>>synchronization is still missed somewhere.
>>>
>>>It might be useful to log the dma_map/unmp in both virtio_ring and 
>>>vringh to see who is missing the map.
>>>
>>
>>Just an update about these issues with vdpa-sim-blk.
>>I've been focusing a little bit on these failures over the last few 
>>days and have found two issues related to the IOTLB/IOMMU:
>>
>>1. Some requests coming from the block layer fills the SG list with 
>>multiple buffers that had the same physical address. This happens 
>>for example while using 'mkfs', at some points multiple sectors
are
>>zeroed so multiple SG elements point to the same physical page that 
>>is zeroed.
>>Since we are using vhost_iotlb_del_range() in the 
>>vdpasim_unmap_page(), this removes all the overlapped ranges. I 
>>fixed removing a single map in vdpasim_unmap_page(), but has an 
>>alternative we can implement some kind of reference counts.
>
>
>I think we need to do what hardware do. So using refcount is probably 
>not a good ida.
Okay, so since we are using for simplicity an identical mapping, we are 
assigning the same dma_addr to multiple pages.

So, it should be okay to remove a single mapping checking the others 
parameters (i.e. dir, size).

I'll send a patch, so with the code it should be easier :-)

Thanks,
Stefano
>
>
>>
>>2. There was a race between dma_map/unmap and the worker thread, 
>>since both are accessing the IOMMU. Taking the iommu_lock while 
>>using vhost_iotlb_* API in the worker thread fixes the "vringh: 
>>Failed to *" issues.
>>
>>Whit these issues fixed the vdpa-blk simulator seems to work well.
>>I'll send the patches next week or after the break.
>
>
>Good to know this.
>
>Thanks
>
>
>>
>>Thanks,
>>Stefano
>>
>