Re: [PATCH 0/7] vhost-vdpa multiqueue fixes

[Jason Wang]

On Wed, Apr 27, 2022 at 5:09 PM Si-Wei Liu <si-wei.liu@oracle.com> wrote:
>
>
>
> On 4/27/2022 1:38 AM, Jason Wang wrote:
> > On Wed, Apr 27, 2022 at 4:30 PM Si-Wei Liu <si-wei.liu@oracle.com> wrote:
> >>
> >>
> >> On 4/26/2022 9:28 PM, Jason Wang wrote:
> >>> 在 2022/3/30 14:33, Si-Wei Liu 写道:
> >>>> Hi,
> >>>>
> >>>> This patch series attempt to fix a few issues in vhost-vdpa
> >>>> multiqueue functionality.
> >>>>
> >>>> Patch #1 is the formal submission for RFC patch in:
> >>>> https://urldefense.com/v3/__https://lore.kernel.org/qemu-devel/c3e931ee-1a1b-9c2f-2f59-cb4395c230f9@oracle.com/__;!!ACWV5N9M2RV99hQ!OoUKcyWauHGQOM4MTAUn88TINQo5ZP4aaYyvyUCK9ggrI_L6diSZo5Nmq55moGH769SD87drxQyqg3ysNsk$
> >>>>
> >>>> Patch #2 and #3 were taken from a previous patchset posted on
> >>>> qemu-devel:
> >>>> https://urldefense.com/v3/__https://lore.kernel.org/qemu-devel/20211117192851.65529-1-eperezma@redhat.com/__;!!ACWV5N9M2RV99hQ!OoUKcyWauHGQOM4MTAUn88TINQo5ZP4aaYyvyUCK9ggrI_L6diSZo5Nmq55moGH769SD87drxQyqc3mXqDs$
> >>>>
> >>>> albeit abandoned, two patches in that set turn out to be useful for
> >>>> patch #4, which is to fix a QEMU crash due to race condition.
> >>>>
> >>>> Patch #5 through #7 are obviously small bug fixes. Please find the
> >>>> description of each in the commit log.
> >>>>
> >>>> Thanks,
> >>>> -Siwei
> >>>
> >>> Hi Si Wei:
> >>>
> >>> I think we need another version of this series?
> >> Hi Jason,
> >>
> >> Apologies for the long delay. I was in the middle of reworking the patch
> >> "virtio: don't read pending event on host notifier if disabled", but
> >> found out that it would need quite some code change for the userspace
> >> fallback handler to work properly (for the queue no. change case
> >> specifically).
> > We probably need this fix for -stable, so I wonder if we can have a
> > workaround first and do refactoring on top?
> Hmmm, a nasty fix but may well address the segfault is something like this:
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 8ca0b80..3ac93a4 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -368,6 +368,10 @@ static void virtio_net_set_status(struct
> VirtIODevice *vdev, uint8_t status)
>       int i;
>       uint8_t queue_status;
>
> +    if (n->status_pending)
> +        return;
> +
> +    n->status_pending = true;
>       virtio_net_vnet_endian_status(n, status);
>       virtio_net_vhost_status(n, status);
>
> @@ -416,6 +420,7 @@ static void virtio_net_set_status(struct
> VirtIODevice *vdev, uint8_t status)
>               }
>           }
>       }
> +    n->status_pending = false;
>   }
>
>   static void virtio_net_set_link_status(NetClientState *nc)
> diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
> index eb87032..95efea8 100644
> --- a/include/hw/virtio/virtio-net.h
> +++ b/include/hw/virtio/virtio-net.h
> @@ -216,6 +216,7 @@ struct VirtIONet {
>       VirtioNetRssData rss_data;
>       struct NetRxPkt *rx_pkt;
>       struct EBPFRSSContext ebpf_rss;
> +    bool status_pending;
>   };
>
>   void virtio_net_set_netclient_name(VirtIONet *n, const char *name,
>
> To be honest, I am not sure if this is worth a full blown fix to make it
> completely work. Without applying vq suspend patch (the one I posted in
> https://lore.kernel.org/qemu-devel/df7c9a87-b2bd-7758-a6b6-bd834a7336fe@oracle.com/),
> it's very hard for me to effectively verify my code change - it's very
> easy for the guest vq index to be out of sync if not stopping the vq
> once the vhost is up and running (I tested it with repeatedly set_link
> off and on).

Can we test via vmstop?

> I am not sure if there's real chance we can run into issue
> in practice due to the incomplete fix, if we don't fix the vq
> stop/suspend issue first. Anyway I will try, as other use case e.g, live
> migration is likely to get stumbled on it, too.

Ok, so I think we probably don't need the "nasty" fix above. Let's fix
it with the issue of stop/resume.

Thanks

>
> -Siwei
>
>
> >
> >> I have to drop it from the series and posted it later on
> >> when ready. Will post a v2 with relevant patches removed.
> > Thanks
> >
> >> Regards,
> >> -Siwei
> >>
> >>> Thanks
> >>>
> >>>
> >>>> ---
> >>>>
> >>>> Eugenio Pérez (2):
> >>>>     virtio-net: Fix indentation
> >>>>     virtio-net: Only enable userland vq if using tap backend
> >>>>
> >>>> Si-Wei Liu (5):
> >>>>     virtio-net: align ctrl_vq index for non-mq guest for vhost_vdpa
> >>>>     virtio: don't read pending event on host notifier if disabled
> >>>>     vhost-vdpa: fix improper cleanup in net_init_vhost_vdpa
> >>>>     vhost-net: fix improper cleanup in vhost_net_start
> >>>>     vhost-vdpa: backend feature should set only once
> >>>>
> >>>>    hw/net/vhost_net.c         |  4 +++-
> >>>>    hw/net/virtio-net.c        | 25 +++++++++++++++++++++----
> >>>>    hw/virtio/vhost-vdpa.c     |  2 +-
> >>>>    hw/virtio/virtio-bus.c     |  3 ++-
> >>>>    hw/virtio/virtio.c         | 21 +++++++++++++--------
> >>>>    include/hw/virtio/virtio.h |  2 ++
> >>>>    net/vhost-vdpa.c           |  4 +++-
> >>>>    7 files changed, 45 insertions(+), 16 deletions(-)
> >>>>
>