Message-ID: <5ec828eb-6012-1d8e-63b1-5dab19095e0c@huawei.com>
Date:   Tue, 14 Feb 2023 10:05:00 +0800
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Subject: Re: [PATCH v3 2/2] vdpasim: support doorbell mapping
To:     "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>
CC:     <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>
References: <20230129025034.2000-1-longpeng2@huawei.com>
 <20230129025034.2000-3-longpeng2@huawei.com>
 <CACGkMEvZsfxQW0fVdy0CpqxoWQzz6z=dYK__xFisncuSRms67A@mail.gmail.com>
 <20230213070446-mutt-send-email-mst@kernel.org>
From:   "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" 
        <longpeng2@huawei.com>
In-Reply-To: <20230213070446-mutt-send-email-mst@kernel.org>
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在 2023/2/13 20:05, Michael S. Tsirkin 写道:
> On Sun, Jan 29, 2023 at 02:19:51PM +0800, Jason Wang wrote:
>> 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()?
> 
> it is just initialization so it should not matter.
> 
I think so.

And WRITE_ONCE seems operate on a variable, but we want write value into 
a specific memory location here.

>>> +
>>>          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
>>>
> 
> .