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

[Si-Wei Liu]

Hi Stefano,

On 10/17/2023 6:44 AM, Stefano Garzarella wrote:
> 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.
I'm sorry, the previous RFC patch was incomplete - please see the v2 I 
just posted. Tested both use_va and !use_va on vdpa-sim-blk, and raw 
disk copy to the vdpa block simulator using dd seems fine. Just let me 
know how it goes on your side this time.

Thanks,
-Siwei

> > > > 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