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Message-ID: <fb3a6ad0-dc79-9b58-3a32-06e3145a4dad@huawei.com>
Date:   Tue, 6 Dec 2022 16:45:42 +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>
From:   "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" 
        <longpeng2@huawei.com>
In-Reply-To: <CACGkMEtdT5fG=ffbpQadkGmzHf6Ax-+L50LsriYqJaW++natMg@mail.gmail.com>
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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.

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
>>
> 
> .