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    SubjectRe: [PATCH 1/2] vdpa/mlx5: Avoid unnecessary query virtqueue
    On Mon, Feb 01, 2021 at 08:15:29PM -0800, Si-Wei Liu wrote:
    > On Mon, Feb 1, 2021 at 7:13 PM Jason Wang <jasowang@redhat.com> wrote:
    > >
    > >
    > > On 2021/2/2 上午3:17, Si-Wei Liu wrote:
    > > > On Mon, Feb 1, 2021 at 10:51 AM Si-Wei Liu <siwliu.kernel@gmail.com> wrote:
    > > >> On Thu, Jan 28, 2021 at 5:46 AM Eli Cohen <elic@nvidia.com> wrote:
    > > >>> suspend_vq should only suspend the VQ on not save the current available
    > > >>> index. This is done when a change of map occurs when the driver calls
    > > >>> save_channel_info().
    > > >> Hmmm, suspend_vq() is also called by teardown_vq(), the latter of
    > > >> which doesn't save the available index as save_channel_info() doesn't
    > > >> get called in that path at all. How does it handle the case that
    > > >> aget_vq_state() is called from userspace (e.g. QEMU) while the
    > > >> hardware VQ object was torn down, but userspace still wants to access
    > > >> the queue index?
    > > >>
    > > >> Refer to https://lore.kernel.org/netdev/1601583511-15138-1-git-send-email-si-wei.liu@oracle.com/
    > > >>
    > > >> vhost VQ 0 ring restore failed: -1: Resource temporarily unavailable (11)
    > > >> vhost VQ 1 ring restore failed: -1: Resource temporarily unavailable (11)
    > > >>
    > > >> QEMU will complain with the above warning while VM is being rebooted
    > > >> or shut down.
    > > >>
    > > >> Looks to me either the kernel driver should cover this requirement, or
    > > >> the userspace has to bear the burden in saving the index and not call
    > > >> into kernel if VQ is destroyed.
    > > > Actually, the userspace doesn't have the insights whether virt queue
    > > > will be destroyed if just changing the device status via set_status().
    > > > Looking at other vdpa driver in tree i.e. ifcvf it doesn't behave like
    > > > so. Hence this still looks to me to be Mellanox specifics and
    > > > mlx5_vdpa implementation detail that shouldn't expose to userspace.
    > >
    > >
    > > So I think we can simply drop this patch?
    >
    > Yep, I think so. To be honest I don't know why it has anything to do
    > with the memory hotplug issue.

    No relation. That's why I put them in two different patches. Only the
    second one is the fix as I stated in the cover letter.

    Anyway, let's just take the second patch.

    Michael, do you need me to send PATCH 2 again as a single patch or can
    you just take it?


    >
    > -Siwei
    >
    > >
    > > Thanks
    > >
    > >
    > > >> -Siwei
    > > >>
    > > >>
    > > >>> Signed-off-by: Eli Cohen <elic@nvidia.com>
    > > >>> ---
    > > >>> drivers/vdpa/mlx5/net/mlx5_vnet.c | 8 --------
    > > >>> 1 file changed, 8 deletions(-)
    > > >>>
    > > >>> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
    > > >>> index 88dde3455bfd..549ded074ff3 100644
    > > >>> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
    > > >>> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
    > > >>> @@ -1148,8 +1148,6 @@ static int setup_vq(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *mvq)
    > > >>>
    > > >>> static void suspend_vq(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *mvq)
    > > >>> {
    > > >>> - struct mlx5_virtq_attr attr;
    > > >>> -
    > > >>> if (!mvq->initialized)
    > > >>> return;
    > > >>>
    > > >>> @@ -1158,12 +1156,6 @@ static void suspend_vq(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *m
    > > >>>
    > > >>> if (modify_virtqueue(ndev, mvq, MLX5_VIRTIO_NET_Q_OBJECT_STATE_SUSPEND))
    > > >>> mlx5_vdpa_warn(&ndev->mvdev, "modify to suspend failed\n");
    > > >>> -
    > > >>> - if (query_virtqueue(ndev, mvq, &attr)) {
    > > >>> - mlx5_vdpa_warn(&ndev->mvdev, "failed to query virtqueue\n");
    > > >>> - return;
    > > >>> - }
    > > >>> - mvq->avail_idx = attr.available_index;
    > > >>> }
    > > >>>
    > > >>> static void suspend_vqs(struct mlx5_vdpa_net *ndev)
    > > >>> --
    > > >>> 2.29.2
    > > >>>
    > >

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