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Date:   Mon, 12 Dec 2022 11:54:00 +0800
From:   "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" 
        <longpeng2@...wei.com>
To:     Jason Wang <jasowang@...hat.com>
CC:     <stefanha@...hat.com>, <mst@...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 v2] vdpasim: support doorbell mapping



在 2022/12/12 11:40, Jason Wang 写道:
> On Mon, Dec 12, 2022 at 8:51 AM Longpeng (Mike, Cloud Infrastructure
> Service Product Dept.) <longpeng2@...wei.com> wrote:
>>
>>
>>
>> 在 2022/12/8 15:37, Jason Wang 写道:
>>> On Tue, Dec 6, 2022 at 4:46 PM Longpeng (Mike, Cloud Infrastructure
>>> Service Product Dept.) <longpeng2@...wei.com> wrote:
>>>>
>>>>
>>>>
>>>> 在 2022/12/6 14:59, Jason Wang 写道:
>>>>> On Mon, Dec 5, 2022 at 9:52 PM 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.
>>>>>>
>>>>>> 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@...wei.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).
>>>>>
>>>> We can support kick mode and passthgourh mode simultaneously now, it is
>>>> a little unnecessary. I would remove it in next version.
>>>>
>>>>>> +
>>>>>>     #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?
>>>>>
>>>> Oh, I had replied you in that thread.
>>>>
>>>> The vm_page_prot of notify mapping VMA 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.
>>>
>>> Ok, but any reason to have a X86 guard for this? This basically makes
>>> it won't work for non-x86 archs?
>>>
>> Because only X86 defines __HAVE_PFNMAP_TRACKING, track_pfn_remap does
>> nothing on other archs.
> 
> Ok, but this seems fragile, as we don't have a guarantee that it won't
> be implemented in the future.
> 
>>
>>> I think the correct way is to introduce a new config_ops to fetch the
>>> correct pgprot. Then we are fine.
>>>
>> Is it worth doing this?
> 
> I think it's worth since it:
> 
> 1) only require small tweak on the vdpa core
> 2) avoid arch specific code in the simulator
> 
>> It seems the vdpasim device is just a special
>> case (using RAM to emulates the notify area) and other real HW devices
>> work fine with the current implementation?
> 
> There's no guarantee that we won't have any other software based vDPA
> devices. We've already had a simulator and VDUSE. And we should not
> exclude the possibility of another one.
> 
Make sense.

Any suggestion for the name of this new config_ops? get_notify_pgprot? 
Or add a new field (pgrot) in vdpa_notification_area?

> Thanks
> 
>>
>>> Thanks
>>>
>>>>
>>>> Otherwise, 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
>>>>
>>>>>> +               *(u16 *)vdpasim->notify = VDPASIM_NOTIFY_DEFVAL;
>>>>>
>>>>> WRITE_ONCE()?
>>>>>
>>>> Okay.
>>>>
>>>>>> +       }
>>>>>> +
>>>>>>            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().
>>>>>
>>>> Okay, thanks.
>>>>
>>>>> 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
>>>>>>
>>>>>
>>>>> .
>>>>
>>>
>>> .
>>
> 
> .

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