Re: [RFC PATCH] vdpa_sim: implement .reset_map support

[Stefano Garzarella]

On Fri, Oct 13, 2023 at 10:29:26AM -0700, Si-Wei Liu wrote:
> Hi Stefano,
>
> On 10/13/2023 2:22 AM, Stefano Garzarella wrote:
> > Hi Si-Wei,
> >
> > On Fri, Oct 13, 2023 at 01:23:40AM -0700, Si-Wei Liu wrote:
> > > RFC only. Not tested on vdpa-sim-blk with user virtual address.
> >
> > I can test it, but what I should stress?
> Great, thank you! As you see, my patch moved vhost_iotlb_reset out of 
> vdpasim_reset for the sake of decoupling mapping from vdpa device 
> reset. For hardware devices this decoupling makes sense as platform 
> IOMMU already did it. But I'm not sure if there's something in the 
> software device (esp. with vdpa-blk and the userspace library stack) 
> that may have to rely on the current .reset behavior that clears the 
> vhost_iotlb. So perhaps you can try to exercise every possible case 
> involving blk device reset, and see if anything (related to mapping) 
> breaks?

I just tried these steps without using a VM and the host kernel hangs
after adding the device:

[root@f38-vm-build ~]# modprobe virtio-vdpa
[root@f38-vm-build ~]# modprobe vdpa-sim-blk
[root@f38-vm-build ~]# vdpa dev add mgmtdev vdpasim_blk name blk0
[   35.284575][  T563] virtio_blk virtio6: 1/0/0 default/read/poll queues
[   35.286372][  T563] virtio_blk virtio6: [vdb] 262144 512-byte logical blocks (134 MB/128 MiB)
[   35.295271][  T564] vringh:

Reverting this patch (so building "vdpa/mlx5: implement .reset_map 
driver op") worked here.

> > > Works fine with vdpa-sim-net which uses physical address to map.
> >
> > Can you share your tests? so I'll try to do the same with blk.
> Basically everything involving virtio device reset in the guest, e.g.  
> reboot the VM, remove/unbind then reprobe/bind the virtio-net 
> module/driver, then see if device I/O (which needs mapping properly) is 
> still flowing as expected. And then everything else that could trigger 
> QEMU's vhost_dev_start/stop paths ending up as passive vhos-vdpa 
> backend reset, for e.g. link status change, suspend/hibernate, SVQ 
> switch and live migration. I am not sure if vdpa-blk supports live 
> migration through SVQ or not, if not you don't need to worry about.
>
> > > This patch is based on top of [1].
> > >
> > > [1] https://lore.kernel.org/virtualization/1696928580-7520-1-git-send-email-si-wei.liu@xxxxxxxxxx/
> >
> > The series does not apply well on master or vhost tree.
> > Where should I apply it?
> Sent the link through another email offline.

Received thanks!

Stefano