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

On 2020/12/21 ??7:14, Stefano Garzarella wrote:
> 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.

I think I get you now. That's the root cause for the failure.

Then I think we need an simple iova allocator for vdpa simulator, and it 
might be useful for VDUSE as well.

Thanks

>
> 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
>>>
>>
>

On Tue, Dec 22, 2020 at 10:44:48AM +0800, Jason Wang
wrote:
>
>On 2020/12/21 ??7:14, Stefano Garzarella wrote:
>>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.
>
>
>I think I get you now. That's the root cause for the failure.
Yes, sorry, I didn't explain well previously.
>
>Then I think we need an simple iova allocator for vdpa simulator, and 
>it might be useful for VDUSE as well.
Okay, I'll work on it.
If you have an example to follow or some pointers, they are welcome :-)

Thanks,
Stefano