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References: <20221205135130.2336-1-longpeng2@huawei.com>
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From:   Jason Wang <jasowang@redhat.com>
Date:   Tue, 6 Dec 2022 14:59:22 +0800
Message-ID: <CACGkMEtdT5fG=ffbpQadkGmzHf6Ax-+L50LsriYqJaW++natMg@mail.gmail.com>
Subject: Re: [PATCH v2] vdpasim: support doorbell mapping
To:     "Longpeng(Mike)" <longpeng2@huawei.com>
Cc:     stefanha@redhat.com, mst@redhat.com, sgarzare@redhat.com,
        eperezma@redhat.com, cohuck@redhat.com, arei.gonglei@huawei.com,
        yechuan@huawei.com, huangzhichao@huawei.com,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
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On Mon, Dec 5, 2022 at 9:52 PM 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 ).
>
> This cap is disabled as default, users can enable it as follow:
>   modprobe vdpa_sim notify_passthrough=true
>
> Signed-off-by: Longpeng <longpeng2@huawei.com>
> ---
> Changes v1->v2:
>   - support both kick mode and passthrough mode. [Jason]
>   - poll the notify register first. [Jason, Michael]
> ---
>  drivers/vdpa/vdpa_sim/vdpa_sim.c | 77 ++++++++++++++++++++++++++++++++
>  drivers/vdpa/vdpa_sim/vdpa_sim.h |  3 ++
>  2 files changed, 80 insertions(+)
>
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> index 7438a89ce939..07096a04dabb 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> @@ -14,6 +14,7 @@
>  #include <linux/slab.h>
>  #include <linux/sched.h>
>  #include <linux/dma-map-ops.h>
> +#include <asm/set_memory.h>
>  #include <linux/vringh.h>
>  #include <linux/vdpa.h>
>  #include <linux/vhost_iotlb.h>
> @@ -36,9 +37,16 @@ module_param(max_iotlb_entries, int, 0444);
>  MODULE_PARM_DESC(max_iotlb_entries,
>                  "Maximum number of iotlb entries for each address space. 0 means unlimited. (default: 2048)");
>
> +static bool notify_passthrough;
> +module_param(notify_passthrough, bool, 0444);
> +MODULE_PARM_DESC(notify_passthrough,
> +                "Enable vq notify(doorbell) area mapping. (default: false)");

I'm not sure if it's worth doing this, I think we can afford the cost
of periodic work (especially considering it's a simulator).

> +
>  #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 +254,28 @@ 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 +317,18 @@ struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr,
>         set_dma_ops(dev, &vdpasim_dma_ops);
>         vdpasim->vdpa.mdev = dev_attr->mgmt_dev;
>
> +       if (notify_passthrough) {
> +               INIT_DELAYED_WORK(&vdpasim->notify_work, vdpasim_notify_work);
> +
> +               vdpasim->notify = __get_free_page(GFP_KERNEL | __GFP_ZERO);
> +               if (!vdpasim->notify)
> +                       goto err_iommu;
> +#ifdef CONFIG_X86
> +               set_memory_uc(vdpasim->notify, 1);
> +#endif

I had the same question with version 1, any reason for having this
part uncacheable? It's a hint that we have bugs somewhere. Are we
missing ACCESS/ORDER_PLATFORM or other features?

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

WRITE_ONCE()?

> +       }
> +
>         vdpasim->config = kzalloc(dev_attr->config_size, GFP_KERNEL);
>         if (!vdpasim->config)
>                 goto err_iommu;
> @@ -495,6 +537,18 @@ static u8 vdpasim_get_status(struct vdpa_device *vdpa)
>         return status;
>  }
>
> +static void vdpasim_set_notify_work(struct vdpasim *vdpasim, bool start)
> +{
> +       if (!notify_passthrough)
> +               return;

Only two callers for this function: one is start another is stop. If
we decide to get rid of notify_passthrough, I'd rather opencode the
schedule/cancel_delayed().

Thanks

> +
> +       if (start)
> +               schedule_delayed_work(&vdpasim->notify_work,
> +                                     msecs_to_jiffies(VDPASIM_VRING_POLL_PERIOD));
> +       else
> +               cancel_delayed_work_sync(&vdpasim->notify_work);
> +}
> +
>  static void vdpasim_set_status(struct vdpa_device *vdpa, u8 status)
>  {
>         struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
> @@ -502,12 +556,14 @@ static void vdpasim_set_status(struct vdpa_device *vdpa, u8 status)
>         spin_lock(&vdpasim->lock);
>         vdpasim->status = status;
>         spin_unlock(&vdpasim->lock);
> +       vdpasim_set_notify_work(vdpasim, status & VIRTIO_CONFIG_S_DRIVER_OK);
>  }
>
>  static int vdpasim_reset(struct vdpa_device *vdpa, bool clear)
>  {
>         struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
>
> +       vdpasim_set_notify_work(vdpasim, false);
>         spin_lock(&vdpasim->lock);
>         vdpasim->status = 0;
>         vdpasim_do_reset(vdpasim);
> @@ -672,11 +728,24 @@ static int vdpasim_dma_unmap(struct vdpa_device *vdpa, unsigned int asid,
>         return 0;
>  }
>
> +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;
>
> +       vdpasim_set_notify_work(vdpasim, false);
>         cancel_work_sync(&vdpasim->work);
>
>         for (i = 0; i < vdpasim->dev_attr.nvqs; i++) {
> @@ -693,6 +762,12 @@ static void vdpasim_free(struct vdpa_device *vdpa)
>         vhost_iotlb_free(vdpasim->iommu);
>         kfree(vdpasim->vqs);
>         kfree(vdpasim->config);
> +       if (vdpasim->notify) {
> +#ifdef CONFIG_X86
> +               set_memory_wb(vdpasim->notify, 1);
> +#endif
> +               free_page(vdpasim->notify);
> +       }
>  }
>
>  static const struct vdpa_config_ops vdpasim_config_ops = {
> @@ -704,6 +779,7 @@ 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_align           = vdpasim_get_vq_align,
>         .get_vq_group           = vdpasim_get_vq_group,
>         .get_device_features    = vdpasim_get_device_features,
> @@ -737,6 +813,7 @@ 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_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
>