linux-kernel - Re: [RFC PATCH] vdpa_sim: implement .reset

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Date:   Tue, 17 Oct 2023 15:44:14 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Si-Wei Liu <si-wei.liu@...cle.com>
Cc:     jasowang@...hat.com, mst@...hat.com, eperezma@...hat.com,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] vdpa_sim: implement .reset_map support

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@...-vm-build ~]# modprobe virtio-vdpa
[root@...-vm-build ~]# modprobe vdpa-sim-blk
[root@...-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@oracle.com/
>>
>>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