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Date:   Tue, 4 Aug 2020 16:53:39 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Zhu, Lingshan" <lingshan.zhu@...el.com>,
        alex.williamson@...hat.com, mst@...hat.com, pbonzini@...hat.com,
        sean.j.christopherson@...el.com, wanpengli@...cent.com
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kvm@...r.kernel.org, eli@...lanox.com, shahafs@...lanox.com,
        parav@...lanox.com
Subject: Re: [PATCH V5 1/6] vhost: introduce vhost_vring_call


On 2020/8/4 下午4:42, Zhu, Lingshan wrote:
>
>
> On 8/4/2020 4:38 PM, Jason Wang wrote:
>>
>> On 2020/7/31 下午2:55, Zhu Lingshan wrote:
>>> This commit introduces struct vhost_vring_call which replaced
>>> raw struct eventfd_ctx *call_ctx in struct vhost_virtqueue.
>>> Besides eventfd_ctx, it contains a spin lock and an
>>> irq_bypass_producer in its structure.
>>>
>>> Signed-off-by: Zhu Lingshan <lingshan.zhu@...el.com>
>>> Suggested-by: Jason Wang <jasowang@...hat.com>
>>> ---
>>>   drivers/vhost/vdpa.c  |  4 ++--
>>>   drivers/vhost/vhost.c | 22 ++++++++++++++++------
>>>   drivers/vhost/vhost.h |  9 ++++++++-
>>>   3 files changed, 26 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
>>> index a54b60d6623f..df3cf386b0cd 100644
>>> --- a/drivers/vhost/vdpa.c
>>> +++ b/drivers/vhost/vdpa.c
>>> @@ -96,7 +96,7 @@ static void handle_vq_kick(struct vhost_work *work)
>>>   static irqreturn_t vhost_vdpa_virtqueue_cb(void *private)
>>>   {
>>>       struct vhost_virtqueue *vq = private;
>>> -    struct eventfd_ctx *call_ctx = vq->call_ctx;
>>> +    struct eventfd_ctx *call_ctx = vq->call_ctx.ctx;
>>>         if (call_ctx)
>>>           eventfd_signal(call_ctx, 1);
>>> @@ -382,7 +382,7 @@ static long vhost_vdpa_vring_ioctl(struct 
>>> vhost_vdpa *v, unsigned int cmd,
>>>           break;
>>>         case VHOST_SET_VRING_CALL:
>>> -        if (vq->call_ctx) {
>>> +        if (vq->call_ctx.ctx) {
>>>               cb.callback = vhost_vdpa_virtqueue_cb;
>>>               cb.private = vq;
>>>           } else {
>>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>>> index d7b8df3edffc..9f1a845a9302 100644
>>> --- a/drivers/vhost/vhost.c
>>> +++ b/drivers/vhost/vhost.c
>>> @@ -298,6 +298,13 @@ static void vhost_vq_meta_reset(struct 
>>> vhost_dev *d)
>>>           __vhost_vq_meta_reset(d->vqs[i]);
>>>   }
>>>   +static void vhost_vring_call_reset(struct vhost_vring_call 
>>> *call_ctx)
>>> +{
>>> +    call_ctx->ctx = NULL;
>>> +    memset(&call_ctx->producer, 0x0, sizeof(struct 
>>> irq_bypass_producer));
>>> +    spin_lock_init(&call_ctx->ctx_lock);
>>> +}
>>> +
>>>   static void vhost_vq_reset(struct vhost_dev *dev,
>>>                  struct vhost_virtqueue *vq)
>>>   {
>>> @@ -319,13 +326,13 @@ static void vhost_vq_reset(struct vhost_dev *dev,
>>>       vq->log_base = NULL;
>>>       vq->error_ctx = NULL;
>>>       vq->kick = NULL;
>>> -    vq->call_ctx = NULL;
>>>       vq->log_ctx = NULL;
>>>       vhost_reset_is_le(vq);
>>>       vhost_disable_cross_endian(vq);
>>>       vq->busyloop_timeout = 0;
>>>       vq->umem = NULL;
>>>       vq->iotlb = NULL;
>>> +    vhost_vring_call_reset(&vq->call_ctx);
>>>       __vhost_vq_meta_reset(vq);
>>>   }
>>>   @@ -685,8 +692,8 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
>>> eventfd_ctx_put(dev->vqs[i]->error_ctx);
>>>           if (dev->vqs[i]->kick)
>>>               fput(dev->vqs[i]->kick);
>>> -        if (dev->vqs[i]->call_ctx)
>>> - eventfd_ctx_put(dev->vqs[i]->call_ctx);
>>> +        if (dev->vqs[i]->call_ctx.ctx)
>>> + eventfd_ctx_put(dev->vqs[i]->call_ctx.ctx);
>>>           vhost_vq_reset(dev, dev->vqs[i]);
>>>       }
>>>       vhost_dev_free_iovecs(dev);
>>> @@ -1629,7 +1636,10 @@ long vhost_vring_ioctl(struct vhost_dev *d, 
>>> unsigned int ioctl, void __user *arg
>>>               r = PTR_ERR(ctx);
>>>               break;
>>>           }
>>> -        swap(ctx, vq->call_ctx);
>>> +
>>> +        spin_lock(&vq->call_ctx.ctx_lock);
>>> +        swap(ctx, vq->call_ctx.ctx);
>>> +        spin_unlock(&vq->call_ctx.ctx_lock);
>>>           break;
>>>       case VHOST_SET_VRING_ERR:
>>>           if (copy_from_user(&f, argp, sizeof f)) {
>>> @@ -2440,8 +2450,8 @@ static bool vhost_notify(struct vhost_dev 
>>> *dev, struct vhost_virtqueue *vq)
>>>   void vhost_signal(struct vhost_dev *dev, struct vhost_virtqueue *vq)
>>>   {
>>>       /* Signal the Guest tell them we used something up. */
>>> -    if (vq->call_ctx && vhost_notify(dev, vq))
>>> -        eventfd_signal(vq->call_ctx, 1);
>>> +    if (vq->call_ctx.ctx && vhost_notify(dev, vq))
>>> +        eventfd_signal(vq->call_ctx.ctx, 1);
>>>   }
>>>   EXPORT_SYMBOL_GPL(vhost_signal);
>>>   diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
>>> index c8e96a095d3b..38eb1aa3b68d 100644
>>> --- a/drivers/vhost/vhost.h
>>> +++ b/drivers/vhost/vhost.h
>>> @@ -13,6 +13,7 @@
>>>   #include <linux/virtio_ring.h>
>>>   #include <linux/atomic.h>
>>>   #include <linux/vhost_iotlb.h>
>>> +#include <linux/irqbypass.h>
>>>     struct vhost_work;
>>>   typedef void (*vhost_work_fn_t)(struct vhost_work *work);
>>> @@ -60,6 +61,12 @@ enum vhost_uaddr_type {
>>>       VHOST_NUM_ADDRS = 3,
>>>   };
>>>   +struct vhost_vring_call {
>>> +    struct eventfd_ctx *ctx;
>>> +    struct irq_bypass_producer producer;
>>> +    spinlock_t ctx_lock;
>>
>>
>> It's not clear to me why we need ctx_lock here.
>>
>> Thanks
> Hi Jason,
>
> we use this lock to protect the eventfd_ctx and irq from race conditions,


We don't support irq notification from vDPA device driver in this 
version, do we still have race condition?

Thanks


>   are you suggesting a better name?
>
> Thanks
>>
>>
>>> +};
>>> +
>>>   /* The virtqueue structure describes a queue attached to a device. */
>>>   struct vhost_virtqueue {
>>>       struct vhost_dev *dev;
>>> @@ -72,7 +79,7 @@ struct vhost_virtqueue {
>>>       vring_used_t __user *used;
>>>       const struct vhost_iotlb_map *meta_iotlb[VHOST_NUM_ADDRS];
>>>       struct file *kick;
>>> -    struct eventfd_ctx *call_ctx;
>>> +    struct vhost_vring_call call_ctx;
>>>       struct eventfd_ctx *error_ctx;
>>>       struct eventfd_ctx *log_ctx;
>>

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