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References: <20230129025034.2000-1-longpeng2@huawei.com> <20230129025034.2000-3-longpeng2@huawei.com>
In-Reply-To: <20230129025034.2000-3-longpeng2@huawei.com>
From:   Jason Wang <jasowang@redhat.com>
Date:   Sun, 29 Jan 2023 14:19:51 +0800
Message-ID: <CACGkMEvZsfxQW0fVdy0CpqxoWQzz6z=dYK__xFisncuSRms67A@mail.gmail.com>
Subject: Re: [PATCH v3 2/2] vdpasim: support doorbell mapping
To:     "Longpeng(Mike)" <longpeng2@huawei.com>
Cc:     mst@redhat.com, stefanha@redhat.com, sgarzare@redhat.com,
        arei.gonglei@huawei.com, yechuan@huawei.com,
        huangzhichao@huawei.com, virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, eperezma@redhat.com
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Precedence: bulk

On Sun, Jan 29, 2023 at 10:51 AM Longpeng(Mike) <longpeng2@huawei.com> wrote:
>
> From: Longpeng <longpeng2@huawei.com>
>
> Support doorbell mapping for vdpasim devices, then we can test the notify
> passthrough feature even if there's no real hardware on hand.
>
> Allocates a dummy page which is used to emulate the notify page of the device,
> all VQs share the same notify register  that initiated to 0xffff. A  periodic
> work will check whether there're requests need to process ( the value of the
> notify register is 0xffff or not ).
> ---
>  drivers/vdpa/vdpa_sim/vdpa_sim.c | 65 ++++++++++++++++++++++++++++++++
>  drivers/vdpa/vdpa_sim/vdpa_sim.h |  3 ++
>  2 files changed, 68 insertions(+)
>
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> index b071f0d842fb..4fcfeb6e2fb8 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> @@ -39,6 +39,8 @@ MODULE_PARM_DESC(max_iotlb_entries,
>  #define VDPASIM_QUEUE_ALIGN PAGE_SIZE
>  #define VDPASIM_QUEUE_MAX 256
>  #define VDPASIM_VENDOR_ID 0
> +#define VDPASIM_VRING_POLL_PERIOD 100 /* ms */
> +#define VDPASIM_NOTIFY_DEFVAL 0xffff
>
>  static struct vdpasim *vdpa_to_sim(struct vdpa_device *vdpa)
>  {
> @@ -246,6 +248,28 @@ static const struct dma_map_ops vdpasim_dma_ops = {
>  static const struct vdpa_config_ops vdpasim_config_ops;
>  static const struct vdpa_config_ops vdpasim_batch_config_ops;
>
> +static void vdpasim_notify_work(struct work_struct *work)
> +{
> +       struct vdpasim *vdpasim;
> +       u16 *val;
> +
> +       vdpasim = container_of(work, struct vdpasim, notify_work.work);
> +
> +       if (!(vdpasim->status & VIRTIO_CONFIG_S_DRIVER_OK))
> +               goto out;
> +
> +       if (!vdpasim->running)
> +               goto out;
> +
> +       val = (u16 *)vdpasim->notify;
> +       if (xchg(val, VDPASIM_NOTIFY_DEFVAL) != VDPASIM_NOTIFY_DEFVAL)
> +               schedule_work(&vdpasim->work);
> +
> +out:
> +       schedule_delayed_work(&vdpasim->notify_work,
> +                             msecs_to_jiffies(VDPASIM_VRING_POLL_PERIOD));
> +}
> +
>  struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr,
>                                const struct vdpa_dev_set_config *config)
>  {
> @@ -287,6 +311,13 @@ struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr,
>         set_dma_ops(dev, &vdpasim_dma_ops);
>         vdpasim->vdpa.mdev = dev_attr->mgmt_dev;
>
> +       INIT_DELAYED_WORK(&vdpasim->notify_work, vdpasim_notify_work);
> +
> +       vdpasim->notify = __get_free_page(GFP_KERNEL | __GFP_ZERO);
> +       if (!vdpasim->notify)
> +               goto err_iommu;

We can simply avoid the advertising notification area in this case.

> +       *(u16 *)vdpasim->notify = VDPASIM_NOTIFY_DEFVAL;

WRITE_ONCE()?

> +
>         vdpasim->config = kzalloc(dev_attr->config_size, GFP_KERNEL);
>         if (!vdpasim->config)
>                 goto err_iommu;
> @@ -498,16 +529,21 @@ static u8 vdpasim_get_status(struct vdpa_device *vdpa)
>  static void vdpasim_set_status(struct vdpa_device *vdpa, u8 status)
>  {
>         struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
> +       bool started = vdpasim->status & VIRTIO_CONFIG_S_DRIVER_OK;

Do we need to do the check under the vdpasim->lock?

>
>         spin_lock(&vdpasim->lock);
>         vdpasim->status = status;
>         spin_unlock(&vdpasim->lock);
> +       if (!started && (status & VIRTIO_CONFIG_S_DRIVER_OK))
> +               schedule_delayed_work(&vdpasim->notify_work,
> +                                     msecs_to_jiffies(VDPASIM_VRING_POLL_PERIOD));
>  }
>
>  static int vdpasim_reset(struct vdpa_device *vdpa)
>  {
>         struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
>
> +       cancel_delayed_work_sync(&vdpasim->notify_work);

Do we need to do this after setting running to zero? Otherwise it's racy.

Thanks

>         spin_lock(&vdpasim->lock);
>         vdpasim->status = 0;
>         vdpasim_do_reset(vdpasim);
> @@ -672,11 +708,34 @@ static int vdpasim_dma_unmap(struct vdpa_device *vdpa, unsigned int asid,
>         return 0;
>  }
>
> +static pgprot_t vdpasim_get_vq_notification_pgprot(struct vdpa_device *vdpa,
> +                                                  u16 qid, pgprot_t prot)
> +{
> +       /*
> +        * We use normal RAM pages to emulate the vq notification area, so
> +        * just keep the pgprot as it mmaped.
> +        */
> +       return prot;
> +}
> +
> +static struct vdpa_notification_area
> +vdpasim_get_vq_notification(struct vdpa_device *vdpa, u16 qid)
> +{
> +       struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
> +       struct vdpa_notification_area notify;
> +
> +       notify.addr = virt_to_phys((void *)vdpasim->notify);
> +       notify.size = PAGE_SIZE;
> +
> +       return notify;
> +}
> +
>  static void vdpasim_free(struct vdpa_device *vdpa)
>  {
>         struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
>         int i;
>
> +       cancel_delayed_work_sync(&vdpasim->notify_work);
>         cancel_work_sync(&vdpasim->work);
>
>         for (i = 0; i < vdpasim->dev_attr.nvqs; i++) {
> @@ -693,6 +752,8 @@ static void vdpasim_free(struct vdpa_device *vdpa)
>         vhost_iotlb_free(vdpasim->iommu);
>         kfree(vdpasim->vqs);
>         kfree(vdpasim->config);
> +       if (vdpasim->notify)
> +               free_page(vdpasim->notify);
>  }
>
>  static const struct vdpa_config_ops vdpasim_config_ops = {
> @@ -704,6 +765,8 @@ static const struct vdpa_config_ops vdpasim_config_ops = {
>         .get_vq_ready           = vdpasim_get_vq_ready,
>         .set_vq_state           = vdpasim_set_vq_state,
>         .get_vq_state           = vdpasim_get_vq_state,
> +       .get_vq_notification    = vdpasim_get_vq_notification,
> +       .get_vq_notification_pgprot = vdpasim_get_vq_notification_pgprot,
>         .get_vq_align           = vdpasim_get_vq_align,
>         .get_vq_group           = vdpasim_get_vq_group,
>         .get_device_features    = vdpasim_get_device_features,
> @@ -737,6 +800,8 @@ static const struct vdpa_config_ops vdpasim_batch_config_ops = {
>         .get_vq_ready           = vdpasim_get_vq_ready,
>         .set_vq_state           = vdpasim_set_vq_state,
>         .get_vq_state           = vdpasim_get_vq_state,
> +       .get_vq_notification    = vdpasim_get_vq_notification,
> +       .get_vq_notification_pgprot = vdpasim_get_vq_notification_pgprot,
>         .get_vq_align           = vdpasim_get_vq_align,
>         .get_vq_group           = vdpasim_get_vq_group,
>         .get_device_features    = vdpasim_get_device_features,
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.h b/drivers/vdpa/vdpa_sim/vdpa_sim.h
> index 0e78737dcc16..0769ccbd3911 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.h
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.h
> @@ -69,6 +69,9 @@ struct vdpasim {
>         bool running;
>         /* spinlock to synchronize iommu table */
>         spinlock_t iommu_lock;
> +       /* dummy notify page */
> +       unsigned long notify;
> +       struct delayed_work notify_work;
>  };
>
>  struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *attr,
> --
> 2.23.0
>