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Date:   Mon, 12 Dec 2022 08:51:03 +0800
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Subject: Re: [PATCH v2] vdpasim: support doorbell mapping
To:     Jason Wang <jasowang@redhat.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>
References: <20221205135130.2336-1-longpeng2@huawei.com>
 <CACGkMEtdT5fG=ffbpQadkGmzHf6Ax-+L50LsriYqJaW++natMg@mail.gmail.com>
 <fb3a6ad0-dc79-9b58-3a32-06e3145a4dad@huawei.com>
 <CACGkMEtgOArE-g8Frp0CkOZRa8F9YbHm5vSoN31X3-BxgT8YNA@mail.gmail.com>
From:   "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" 
        <longpeng2@huawei.com>
In-Reply-To: <CACGkMEtgOArE-g8Frp0CkOZRa8F9YbHm5vSoN31X3-BxgT8YNA@mail.gmail.com>
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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@huawei.com> wrote:
>>
>>
>>
>> 在 2022/12/6 14:59, Jason Wang 写道:
>>> 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).
>>>
>> 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.

> 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? 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?

> 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
>>>>
>>>
>>> .
>>
> 
> .