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Message-ID: <28c1ae52-38ff-42ce-4331-11f7aa040296@huawei.com>
Date:   Mon, 28 Nov 2022 19:59:33 +0800
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Subject: Re: [PATCH] vdpasim: support doorbell mapping
To:     "Michael S. Tsirkin" <mst@redhat.com>
CC:     Jason Wang <jasowang@redhat.com>, <stefanha@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: <20221128025558.2152-1-longpeng2@huawei.com>
 <CACGkMEsWoM1LKkPWPgDALssjkk4UXxfhYm3_aCFktNnpXtWVjQ@mail.gmail.com>
 <53edc14a-74bb-f9c7-06bd-7ea1047fe613@huawei.com>
 <20221128051555-mutt-send-email-mst@kernel.org>
From:   "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" 
        <longpeng2@huawei.com>
In-Reply-To: <20221128051555-mutt-send-email-mst@kernel.org>
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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@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.
>>>
>>> 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.

> 
>>> 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@huawei.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
>>>>
>>>
>>> .
> 
> .