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

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Message-ID: <2222edd1-4eb1-4b06-87ef-df2d4f591931@oracle.com>
Date:   Fri, 13 Oct 2023 10:29:26 -0700
From:   Si-Wei Liu <si-wei.liu@...cle.com>
To:     Stefano Garzarella <sgarzare@...hat.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

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?

>
>> 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.

Thanks,
-Siwei

>
> If you have a tree with all of them applied, will be easy for me ;-)
>
> Thanks,
> Stefano
>