Re: [PATCH RFC 00/12] vdpa: generalize vdpa simulator and add block device

[Jason Wang]

On 2020/12/22 下午6:57, Stefano Garzarella wrote:
> On Tue, Dec 22, 2020 at 10:44:48AM +0800, Jason Wang wrote:
> > On 2020/12/21 下午7:14, Stefano Garzarella wrote:
> > > On Mon, Dec 21, 2020 at 11:16:54AM +0800, Jason Wang wrote:
> > > > On 2020/12/18 下午7:38, Stefano Garzarella wrote:
> > > > > On Mon, Nov 16, 2020 at 11:37:48AM +0800, Jason Wang wrote:
> > > > > > On 2020/11/13 下午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 :-)


Kernel had implemented one in iova.c but I'm not sure we need the 
complexity like that. Or we can just use rbtree or idr to implement a 
simpler one.

Thanks


> Thanks,
> Stefano