Date:   Mon, 28 Nov 2022 22:35:51 +0800
From:   "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" 
        <longpeng2@...wei.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     Jason Wang <jasowang@...hat.com>, <stefanha@...hat.com>,
        <sgarzare@...hat.com>, <eperezma@...hat.com>, <cohuck@...hat.com>,
        <arei.gonglei@...wei.com>, <yechuan@...wei.com>,
        <huangzhichao@...wei.com>,
        <virtualization@...ts.linux-foundation.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] vdpasim: support doorbell mapping



在 2022/11/28 22:17, Michael S. Tsirkin 写道:
> On Mon, Nov 28, 2022 at 09:20:21PM +0800, Longpeng (Mike, Cloud Infrastructure Service Product Dept.) wrote:
>>
>>
>> 在 2022/11/28 20:20, Michael S. Tsirkin 写道:
>>> On Mon, Nov 28, 2022 at 07:59:33PM +0800, Longpeng (Mike, Cloud Infrastructure Service Product Dept.) wrote:
>>>>
>>>>
>>>> 在 2022/11/28 18:19, Michael S. Tsirkin 写道:
>>>>> On Mon, Nov 28, 2022 at 04:19:30PM +0800, Longpeng (Mike, Cloud Infrastructure Service Product Dept.) wrote:
>>>>>>
>>>>>>
>>>>>> 在 2022/11/28 12:05, Jason Wang 写道:
>>>>>>> On Mon, Nov 28, 2022 at 10:56 AM Longpeng(Mike) <longpeng2@...wei.com> wrote:
>>>>>>>>
>>>>>>>> From: Longpeng <longpeng2@...wei.com>
>>>>>>>>
>>>>>>>> Support doorbell mapping for vdpasim devices, then we can test the notify
>>>>>>>> passthrough feature even if there's no real hardware on hand.
>>>>>>>
>>>>>>> You can use vp_vdpa in L1 plus page_ver_vq in L0 to test it in L2.
>>>>>>> That is how I test it.
>>>>>>>
>>>>>> Yes, using nested virtualization can work, but it's hard to deploy in my
>>>>>> working environment for some reasons, so I decided to emulate this
>>>>>> capability in vdpasim, it's much easier.
>>>>>>
>>>>>>>>
>>>>>>>> Allocates a dummy page which used to emulate the notify page of the device.
>>>>>>>> All values written to this page would be ignored,  a periodic work will
>>>>>>>> check whether there're requests that need to process.
>>>>>>>
>>>>>>> This seems tricky, it means the device is working even if there's no
>>>>>>
>>>>>> Right. It just try to make the vdpasim device work properly, but the vdpasim
>>>>>> device is only used for testing, so maybe the tricky emulation is
>>>>>> acceptable?
>>>>>
>>>>> Maybe. You can try enabling VIRTIO_F_NOTIFICATION_DATA and then
>>>>> looking at the data written to figure out whether
>>>>> you need to poll the vq.
>>>>>
>>>> We can try after the kernel supports the VIRTIO_F_NOTIFICATION_DATA feature,
>>>> while there is still a long way to go.
>>>
>>> That would be up to you to implement ;) It's probably 10-20 lines of
>>> code all in all.
>>>
>>
>> Um...The kick operation won't trigger VMEXIT if we support notify mapping
>> for the vdpasim device.
>> So, does the vdpasim device has to poll the notify
>> address and then decide which VQ to poll?
>> The pro of this approach is we can poll the notify address first instead of
>> the unconditional poll the VQ, right?
> 
> Right. In fact you can do this without VIRTIO_F_NOTIFICATION_DATA too,
> just write 0xffff before checking the vq.
> 
Yes, this can work. I will try it in the next version if there're no 
other objections.

>>
>>>>>
>>>>>>> kick. If we really want to do, we should try to use page fault handler
>>>>>>> (probably by extending the config ops), but I'm not sure it's worth to
>>>>>>> bother (or if we can find a use case for no simulator devices).
>>>>>>>
>>>>>> This need to modify the framework, it seems unworthy.
>>>>>>
>>>>>>>>
>>>>>>>> This cap is disabled as default, users can enable it as follow:
>>>>>>>>       modprobe vdpa_sim notify_passthrough=true
>>>>>>>>
>>>>>>>> Signed-off-by: Longpeng <longpeng2@...wei.com>
>>>>>>>> ---
>>>>>>>>      drivers/vdpa/vdpa_sim/vdpa_sim.c     | 71 ++++++++++++++++++++++++++--
>>>>>>>>      drivers/vdpa/vdpa_sim/vdpa_sim.h     |  5 +-
>>>>>>>>      drivers/vdpa/vdpa_sim/vdpa_sim_blk.c |  5 +-
>>>>>>>>      drivers/vdpa/vdpa_sim/vdpa_sim_net.c |  4 +-
>>>>>>>>      4 files changed, 76 insertions(+), 9 deletions(-)
>>>>>>>>
>>>>>>>> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
>>>>>>>> index 7438a89ce939..5c215b56b78b 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 +37,15 @@ 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)");
>>>>>>>> +
>>>>>>>>      #define VDPASIM_QUEUE_ALIGN PAGE_SIZE
>>>>>>>>      #define VDPASIM_QUEUE_MAX 256
>>>>>>>>      #define VDPASIM_VENDOR_ID 0
>>>>>>>> +#define VDPASIM_VRING_POLL_PERIOD 100 /* ms */
>>>>>>>>
>>>>>>>>      static struct vdpasim *vdpa_to_sim(struct vdpa_device *vdpa)
>>>>>>>>      {
>>>>>>>> @@ -276,7 +283,7 @@ struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr,
>>>>>>>>             }
>>>>>>>>
>>>>>>>>             vdpasim->dev_attr = *dev_attr;
>>>>>>>> -       INIT_WORK(&vdpasim->work, dev_attr->work_fn);
>>>>>>>> +       INIT_DELAYED_WORK(&vdpasim->vring_work, dev_attr->work_fn);
>>>>>>>>             spin_lock_init(&vdpasim->lock);
>>>>>>>>             spin_lock_init(&vdpasim->iommu_lock);
>>>>>>>>
>>>>>>>> @@ -287,6 +294,15 @@ 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) {
>>>>>>>> +               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
>>>>>>>
>>>>>>> What's the reason for using uc memory?
>>>>>>>
>>>>>> The vma->vm_page_prot of notify mapping is pgprot_noncached (see
>>>>>> vhost_vdpa_fault) but the vdpasim->notify is WB, so we should set its
>>>>>> memtype to UC here and set it back to WB when releasing the device.
>>>>>
>>>>> You never look at this memory though. Why does it matter whether
>>>>> it's UC or WB?
>>>>>
>>>>
>>>> The warning in trace_pfn_remap() would be triggered.
>>>>
>>>> For example:
>>>>
>>>> x86/PAT: CPU 16/KVM:17819 map pfn RAM range req uncached-minus for [mem
>>>> 0x5151f3000-0x5151f3fff], got write-back
>>>>
>>>>
>>>>>>>> +       }
>>>>>>>> +
>>>>>>>>             vdpasim->config = kzalloc(dev_attr->config_size, GFP_KERNEL);
>>>>>>>>             if (!vdpasim->config)
>>>>>>>>                     goto err_iommu;
>>>>>>>> @@ -357,8 +373,11 @@ static void vdpasim_kick_vq(struct vdpa_device *vdpa, u16 idx)
>>>>>>>>             struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
>>>>>>>>             struct vdpasim_virtqueue *vq = &vdpasim->vqs[idx];
>>>>>>>>
>>>>>>>> +       if (notify_passthrough)
>>>>>>>> +               return;
>>>>>>>
>>>>>>> So we should keep the two paths to be used at the same time. Userspace
>>>>>>> can choose to not map doorbells?
>>>>>>>
>>>>>> It can work even if the userspace does not to map doorbells (e.g start
>>>>>> without page-per-vq=on), because the device will periodic check its vqs.
>>>>>>
>>>>>>> Thanks
>>>>>>>
>>>>>>>> +
>>>>>>>>             if (vq->ready)
>>>>>>>> -               schedule_work(&vdpasim->work);
>>>>>>>> +               schedule_work(&vdpasim->vring_work.work);
>>>>>>>>      }
>>>>>>>>
>>>>>>>>      static void vdpasim_set_vq_cb(struct vdpa_device *vdpa, u16 idx,
>>>>>>>> @@ -495,6 +514,18 @@ static u8 vdpasim_get_status(struct vdpa_device *vdpa)
>>>>>>>>             return status;
>>>>>>>>      }
>>>>>>>>
>>>>>>>> +static void vdpasim_set_vring_work(struct vdpasim *vdpasim, bool start)
>>>>>>>> +{
>>>>>>>> +       if (!notify_passthrough)
>>>>>>>> +               return;
>>>>>>>> +
>>>>>>>> +       if (start)
>>>>>>>> +               schedule_delayed_work(&vdpasim->vring_work,
>>>>>>>> +                               msecs_to_jiffies(VDPASIM_VRING_POLL_PERIOD));
>>>>>>>> +       else
>>>>>>>> +               cancel_delayed_work_sync(&vdpasim->vring_work);
>>>>>>>> +}
>>>>>>>> +
>>>>>>>>      static void vdpasim_set_status(struct vdpa_device *vdpa, u8 status)
>>>>>>>>      {
>>>>>>>>             struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
>>>>>>>> @@ -502,12 +533,16 @@ static void vdpasim_set_status(struct vdpa_device *vdpa, u8 status)
>>>>>>>>             spin_lock(&vdpasim->lock);
>>>>>>>>             vdpasim->status = status;
>>>>>>>>             spin_unlock(&vdpasim->lock);
>>>>>>>> +
>>>>>>>> +       vdpasim_set_vring_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_vring_work(vdpasim, false);
>>>>>>>> +
>>>>>>>>             spin_lock(&vdpasim->lock);
>>>>>>>>             vdpasim->status = 0;
>>>>>>>>             vdpasim_do_reset(vdpasim);
>>>>>>>> @@ -672,12 +707,24 @@ 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;
>>>>>>>>
>>>>>>>> -       cancel_work_sync(&vdpasim->work);
>>>>>>>> +       cancel_delayed_work_sync(&vdpasim->vring_work);
>>>>>>>>
>>>>>>>>             for (i = 0; i < vdpasim->dev_attr.nvqs; i++) {
>>>>>>>>                     vringh_kiov_cleanup(&vdpasim->vqs[i].out_iov);
>>>>>>>> @@ -693,7 +740,23 @@ 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);
>>>>>>>> +       }
>>>>>>>> +}
>>>>>>>> +
>>>>>>>> +void vdpasim_schedule_work(struct vdpasim *vdpasim, bool sched_now)
>>>>>>>> +{
>>>>>>>> +       if (sched_now)
>>>>>>>> +               schedule_work(&vdpasim->vring_work.work);
>>>>>>>> +       else if (notify_passthrough)
>>>>>>>> +               schedule_delayed_work(&vdpasim->vring_work,
>>>>>>>> +                                     msecs_to_jiffies(VDPASIM_VRING_POLL_PERIOD));
>>>>>>>>      }
>>>>>>>> +EXPORT_SYMBOL_GPL(vdpasim_schedule_work);
>>>>>>>>
>>>>>>>>      static const struct vdpa_config_ops vdpasim_config_ops = {
>>>>>>>>             .set_vq_address         = vdpasim_set_vq_address,
>>>>>>>> @@ -704,6 +767,7 @@ 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 +801,7 @@ 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..da0866834918 100644
>>>>>>>> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.h
>>>>>>>> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.h
>>>>>>>> @@ -53,7 +53,7 @@ struct vdpasim_dev_attr {
>>>>>>>>      struct vdpasim {
>>>>>>>>             struct vdpa_device vdpa;
>>>>>>>>             struct vdpasim_virtqueue *vqs;
>>>>>>>> -       struct work_struct work;
>>>>>>>> +       struct delayed_work vring_work;
>>>>>>>>             struct vdpasim_dev_attr dev_attr;
>>>>>>>>             /* spinlock to synchronize virtqueue state */
>>>>>>>>             spinlock_t lock;
>>>>>>>> @@ -69,10 +69,13 @@ struct vdpasim {
>>>>>>>>             bool running;
>>>>>>>>             /* spinlock to synchronize iommu table */
>>>>>>>>             spinlock_t iommu_lock;
>>>>>>>> +       /* dummy notify page */
>>>>>>>> +       unsigned long notify;
>>>>>>>>      };
>>>>>>>>
>>>>>>>>      struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *attr,
>>>>>>>>                                    const struct vdpa_dev_set_config *config);
>>>>>>>> +void vdpasim_schedule_work(struct vdpasim *vdpasim, bool sched_now);
>>>>>>>>
>>>>>>>>      /* TODO: cross-endian support */
>>>>>>>>      static inline bool vdpasim_is_little_endian(struct vdpasim *vdpasim)
>>>>>>>> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c b/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
>>>>>>>> index c6db1a1baf76..8a640ea82284 100644
>>>>>>>> --- a/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
>>>>>>>> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
>>>>>>>> @@ -288,7 +288,7 @@ static bool vdpasim_blk_handle_req(struct vdpasim *vdpasim,
>>>>>>>>
>>>>>>>>      static void vdpasim_blk_work(struct work_struct *work)
>>>>>>>>      {
>>>>>>>> -       struct vdpasim *vdpasim = container_of(work, struct vdpasim, work);
>>>>>>>> +       struct vdpasim *vdpasim = container_of(work, struct vdpasim, vring_work.work);
>>>>>>>>             bool reschedule = false;
>>>>>>>>             int i;
>>>>>>>>
>>>>>>>> @@ -325,8 +325,7 @@ static void vdpasim_blk_work(struct work_struct *work)
>>>>>>>>      out:
>>>>>>>>             spin_unlock(&vdpasim->lock);
>>>>>>>>
>>>>>>>> -       if (reschedule)
>>>>>>>> -               schedule_work(&vdpasim->work);
>>>>>>>> +       vdpasim_schedule_work(vdpasim, reschedule);
>>>>>>>>      }
>>>>>>>>
>>>>>>>>      static void vdpasim_blk_get_config(struct vdpasim *vdpasim, void *config)
>>>>>>>> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim_net.c b/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
>>>>>>>> index c3cb225ea469..8b998952384b 100644
>>>>>>>> --- a/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
>>>>>>>> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
>>>>>>>> @@ -145,7 +145,7 @@ static void vdpasim_handle_cvq(struct vdpasim *vdpasim)
>>>>>>>>
>>>>>>>>      static void vdpasim_net_work(struct work_struct *work)
>>>>>>>>      {
>>>>>>>> -       struct vdpasim *vdpasim = container_of(work, struct vdpasim, work);
>>>>>>>> +       struct vdpasim *vdpasim = container_of(work, struct vdpasim, vring_work.work);
>>>>>>>>             struct vdpasim_virtqueue *txq = &vdpasim->vqs[1];
>>>>>>>>             struct vdpasim_virtqueue *rxq = &vdpasim->vqs[0];
>>>>>>>>             ssize_t read, write;
>>>>>>>> @@ -196,7 +196,7 @@ static void vdpasim_net_work(struct work_struct *work)
>>>>>>>>                     vdpasim_net_complete(rxq, write);
>>>>>>>>
>>>>>>>>                     if (++pkts > 4) {
>>>>>>>> -                       schedule_work(&vdpasim->work);
>>>>>>>> +                       vdpasim_schedule_work(vdpasim, true);
>>>>>>>>                             goto out;
>>>>>>>>                     }
>>>>>>>>             }
>>>>>>>> --
>>>>>>>> 2.23.0
>>>>>>>>
>>>>>>>
>>>>>>> .
>>>>>
>>>>> .
>>>
>>> .
> 
> .

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