[dpdk-dev] [PATCH] vhost: fix vhost interrupt support

[dpdk-dev] [PATCH] vhost: fix vhost interrupt support

[Tiwei Bie]

When VIRTIO_RING_F_EVENT_IDX is negotiated, we need to
update the avail event to enable the notification.

Fixes: 3f8ff12821e4 ("vhost: support interrupt mode")
Cc: stable@dpdk.org

Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
---
 lib/librte_vhost/Makefile |  1 +
 lib/librte_vhost/vhost.c  | 18 ++++++++++++------
 lib/librte_vhost/vhost.h  |  2 ++
 3 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/lib/librte_vhost/Makefile b/lib/librte_vhost/Makefile
index de431fbb7..531cf4832 100644
--- a/lib/librte_vhost/Makefile
+++ b/lib/librte_vhost/Makefile
@@ -13,6 +13,7 @@ LIBABIVER := 4
 CFLAGS += -DALLOW_EXPERIMENTAL_API
 CFLAGS += $(WERROR_FLAGS) -I$(SRCDIR) -O3 -D_FILE_OFFSET_BITS=64
 CFLAGS += -I vhost_user
+CFLAGS += -fno-strict-aliasing
 LDLIBS += -lpthread
 
 ifeq ($(CONFIG_RTE_LIBRTE_VHOST_NUMA),y)
diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
index 3c9be10a0..88b1781d5 100644
--- a/lib/librte_vhost/vhost.c
+++ b/lib/librte_vhost/vhost.c
@@ -646,12 +646,18 @@ rte_vhost_avail_entries(int vid, uint16_t queue_id)
 }
 
 static inline void
-vhost_enable_notify_split(struct vhost_virtqueue *vq, int enable)
+vhost_enable_notify_split(struct virtio_net *dev,
+		struct vhost_virtqueue *vq, int enable)
 {
-	if (enable)
-		vq->used->flags &= ~VRING_USED_F_NO_NOTIFY;
-	else
-		vq->used->flags |= VRING_USED_F_NO_NOTIFY;
+	if (!(dev->features & (1ULL << VIRTIO_RING_F_EVENT_IDX))) {
+		if (enable)
+			vq->used->flags &= ~VRING_USED_F_NO_NOTIFY;
+		else
+			vq->used->flags |= VRING_USED_F_NO_NOTIFY;
+	} else {
+		if (enable)
+			vhost_avail_event(vq) = vq->last_avail_idx;
+	}
 }
 
 static inline void
@@ -689,7 +695,7 @@ rte_vhost_enable_guest_notification(int vid, uint16_t queue_id, int enable)
 	if (vq_is_packed(dev))
 		vhost_enable_notify_packed(dev, vq, enable);
 	else
-		vhost_enable_notify_split(vq, enable);
+		vhost_enable_notify_split(dev, vq, enable);
 
 	return 0;
 }
diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
index 760a09c0d..25ffd7614 100644
--- a/lib/librte_vhost/vhost.h
+++ b/lib/librte_vhost/vhost.h
@@ -648,6 +648,8 @@ vhost_iova_to_vva(struct virtio_net *dev, struct vhost_virtqueue *vq,
 	return __vhost_iova_to_vva(dev, vq, iova, len, perm);
 }
 
+#define vhost_avail_event(vr) \
+	(*(volatile uint16_t*)&(vr)->used->ring[(vr)->size])
 #define vhost_used_event(vr) \
 	(*(volatile uint16_t*)&(vr)->avail->ring[(vr)->size])
 
-- 
2.18.0

Re: [dpdk-dev] [PATCH] vhost: fix vhost interrupt support

[Maxime Coquelin]

Hi Tiwei,

On 09/05/2018 01:55 AM, Tiwei Bie wrote:
> When VIRTIO_RING_F_EVENT_IDX is negotiated, we need to
> update the avail event to enable the notification.
> 
> Fixes: 3f8ff12821e4 ("vhost: support interrupt mode")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
> ---
>   lib/librte_vhost/Makefile |  1 +
>   lib/librte_vhost/vhost.c  | 18 ++++++++++++------
>   lib/librte_vhost/vhost.h  |  2 ++
>   3 files changed, 15 insertions(+), 6 deletions(-)
> 
> diff --git a/lib/librte_vhost/Makefile b/lib/librte_vhost/Makefile
> index de431fbb7..531cf4832 100644
> --- a/lib/librte_vhost/Makefile
> +++ b/lib/librte_vhost/Makefile
> @@ -13,6 +13,7 @@ LIBABIVER := 4
>   CFLAGS += -DALLOW_EXPERIMENTAL_API
>   CFLAGS += $(WERROR_FLAGS) -I$(SRCDIR) -O3 -D_FILE_OFFSET_BITS=64
>   CFLAGS += -I vhost_user
> +CFLAGS += -fno-strict-aliasing

I'm not clear why this is needed looking at the code below,
could you please explain?

>   LDLIBS += -lpthread
>   
>   ifeq ($(CONFIG_RTE_LIBRTE_VHOST_NUMA),y)
> diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
> index 3c9be10a0..88b1781d5 100644
> --- a/lib/librte_vhost/vhost.c
> +++ b/lib/librte_vhost/vhost.c
> @@ -646,12 +646,18 @@ rte_vhost_avail_entries(int vid, uint16_t queue_id)
>   }
>   
>   static inline void
> -vhost_enable_notify_split(struct vhost_virtqueue *vq, int enable)
> +vhost_enable_notify_split(struct virtio_net *dev,
> +		struct vhost_virtqueue *vq, int enable)
>   {
> -	if (enable)
> -		vq->used->flags &= ~VRING_USED_F_NO_NOTIFY;
> -	else
> -		vq->used->flags |= VRING_USED_F_NO_NOTIFY;
> +	if (!(dev->features & (1ULL << VIRTIO_RING_F_EVENT_IDX))) {
> +		if (enable)
> +			vq->used->flags &= ~VRING_USED_F_NO_NOTIFY;
> +		else
> +			vq->used->flags |= VRING_USED_F_NO_NOTIFY;
> +	} else {
> +		if (enable)
> +			vhost_avail_event(vq) = vq->last_avail_idx;
> +	}
>   }
>   
>   static inline void
> @@ -689,7 +695,7 @@ rte_vhost_enable_guest_notification(int vid, uint16_t queue_id, int enable)
>   	if (vq_is_packed(dev))
>   		vhost_enable_notify_packed(dev, vq, enable);
>   	else
> -		vhost_enable_notify_split(vq, enable);
> +		vhost_enable_notify_split(dev, vq, enable);
>   
>   	return 0;
>   }
> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> index 760a09c0d..25ffd7614 100644
> --- a/lib/librte_vhost/vhost.h
> +++ b/lib/librte_vhost/vhost.h
> @@ -648,6 +648,8 @@ vhost_iova_to_vva(struct virtio_net *dev, struct vhost_virtqueue *vq,
>   	return __vhost_iova_to_vva(dev, vq, iova, len, perm);
>   }
>   
> +#define vhost_avail_event(vr) \
> +	(*(volatile uint16_t*)&(vr)->used->ring[(vr)->size])
>   #define vhost_used_event(vr) \
>   	(*(volatile uint16_t*)&(vr)->avail->ring[(vr)->size])
>   
> 

Re: [dpdk-dev] [PATCH] vhost: fix vhost interrupt support

[Tiwei Bie]

Hi Maxime,

On Mon, Sep 10, 2018 at 09:22:00AM +0200, Maxime Coquelin wrote:
> Hi Tiwei,
> 
> On 09/05/2018 01:55 AM, Tiwei Bie wrote:
> > When VIRTIO_RING_F_EVENT_IDX is negotiated, we need to
> > update the avail event to enable the notification.
> > 
> > Fixes: 3f8ff12821e4 ("vhost: support interrupt mode")
> > Cc: stable@dpdk.org
> > 
> > Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
> > ---
> >   lib/librte_vhost/Makefile |  1 +
> >   lib/librte_vhost/vhost.c  | 18 ++++++++++++------
> >   lib/librte_vhost/vhost.h  |  2 ++
> >   3 files changed, 15 insertions(+), 6 deletions(-)
> > 
> > diff --git a/lib/librte_vhost/Makefile b/lib/librte_vhost/Makefile
> > index de431fbb7..531cf4832 100644
> > --- a/lib/librte_vhost/Makefile
> > +++ b/lib/librte_vhost/Makefile
> > @@ -13,6 +13,7 @@ LIBABIVER := 4
> >   CFLAGS += -DALLOW_EXPERIMENTAL_API
> >   CFLAGS += $(WERROR_FLAGS) -I$(SRCDIR) -O3 -D_FILE_OFFSET_BITS=64
> >   CFLAGS += -I vhost_user
> > +CFLAGS += -fno-strict-aliasing
> 
> I'm not clear why this is needed looking at the code below,
> could you please explain?

Without this, we will get below build error:

lib/librte_vhost/vhost.c: In function ‘vhost_enable_notify_split’:
lib/librte_vhost/vhost.h:656:4: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
  (*(volatile uint16_t*)&(vr)->used->ring[(vr)->size])
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
lib/librte_vhost/vhost.c:659:4: note: in expansion of macro ‘vhost_avail_event’
    vhost_avail_event(vq) = vq->last_avail_idx;
    ^~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

> 
> >   LDLIBS += -lpthread
> >   ifeq ($(CONFIG_RTE_LIBRTE_VHOST_NUMA),y)
> > diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
> > index 3c9be10a0..88b1781d5 100644
> > --- a/lib/librte_vhost/vhost.c
> > +++ b/lib/librte_vhost/vhost.c
> > @@ -646,12 +646,18 @@ rte_vhost_avail_entries(int vid, uint16_t queue_id)
> >   }
> >   static inline void
> > -vhost_enable_notify_split(struct vhost_virtqueue *vq, int enable)
> > +vhost_enable_notify_split(struct virtio_net *dev,
> > +		struct vhost_virtqueue *vq, int enable)
> >   {
> > -	if (enable)
> > -		vq->used->flags &= ~VRING_USED_F_NO_NOTIFY;
> > -	else
> > -		vq->used->flags |= VRING_USED_F_NO_NOTIFY;
> > +	if (!(dev->features & (1ULL << VIRTIO_RING_F_EVENT_IDX))) {
> > +		if (enable)
> > +			vq->used->flags &= ~VRING_USED_F_NO_NOTIFY;
> > +		else
> > +			vq->used->flags |= VRING_USED_F_NO_NOTIFY;
> > +	} else {
> > +		if (enable)
> > +			vhost_avail_event(vq) = vq->last_avail_idx;
> > +	}
> >   }
> >   static inline void
> > @@ -689,7 +695,7 @@ rte_vhost_enable_guest_notification(int vid, uint16_t queue_id, int enable)
> >   	if (vq_is_packed(dev))
> >   		vhost_enable_notify_packed(dev, vq, enable);
> >   	else
> > -		vhost_enable_notify_split(vq, enable);
> > +		vhost_enable_notify_split(dev, vq, enable);
> >   	return 0;
> >   }
> > diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> > index 760a09c0d..25ffd7614 100644
> > --- a/lib/librte_vhost/vhost.h
> > +++ b/lib/librte_vhost/vhost.h
> > @@ -648,6 +648,8 @@ vhost_iova_to_vva(struct virtio_net *dev, struct vhost_virtqueue *vq,
> >   	return __vhost_iova_to_vva(dev, vq, iova, len, perm);
> >   }
> > +#define vhost_avail_event(vr) \
> > +	(*(volatile uint16_t*)&(vr)->used->ring[(vr)->size])
> >   #define vhost_used_event(vr) \
> >   	(*(volatile uint16_t*)&(vr)->avail->ring[(vr)->size])
> > 

Re: [dpdk-dev] [PATCH] vhost: fix vhost interrupt support

[Maxime Coquelin]

On 09/10/2018 09:36 AM, Tiwei Bie wrote:
> Hi Maxime,
> 
> On Mon, Sep 10, 2018 at 09:22:00AM +0200, Maxime Coquelin wrote:
>> Hi Tiwei,
>>
>> On 09/05/2018 01:55 AM, Tiwei Bie wrote:
>>> When VIRTIO_RING_F_EVENT_IDX is negotiated, we need to
>>> update the avail event to enable the notification.
>>>
>>> Fixes: 3f8ff12821e4 ("vhost: support interrupt mode")
>>> Cc: stable@dpdk.org
>>>
>>> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
>>> ---
>>>    lib/librte_vhost/Makefile |  1 +
>>>    lib/librte_vhost/vhost.c  | 18 ++++++++++++------
>>>    lib/librte_vhost/vhost.h  |  2 ++
>>>    3 files changed, 15 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/lib/librte_vhost/Makefile b/lib/librte_vhost/Makefile
>>> index de431fbb7..531cf4832 100644
>>> --- a/lib/librte_vhost/Makefile
>>> +++ b/lib/librte_vhost/Makefile
>>> @@ -13,6 +13,7 @@ LIBABIVER := 4
>>>    CFLAGS += -DALLOW_EXPERIMENTAL_API
>>>    CFLAGS += $(WERROR_FLAGS) -I$(SRCDIR) -O3 -D_FILE_OFFSET_BITS=64
>>>    CFLAGS += -I vhost_user
>>> +CFLAGS += -fno-strict-aliasing
>>
>> I'm not clear why this is needed looking at the code below,
>> could you please explain?
> 
> Without this, we will get below build error:
> 
> lib/librte_vhost/vhost.c: In function ‘vhost_enable_notify_split’:
> lib/librte_vhost/vhost.h:656:4: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
>    (*(volatile uint16_t*)&(vr)->used->ring[(vr)->size])
>      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> lib/librte_vhost/vhost.c:659:4: note: in expansion of macro ‘vhost_avail_event’
>      vhost_avail_event(vq) = vq->last_avail_idx;
>      ^~~~~~~~~~~~~~~~~
> cc1: all warnings being treated as errors

OK, thanks for the info.

Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

Maxime

Re: [dpdk-dev] [PATCH] vhost: fix vhost interrupt support

[Maxime Coquelin]

On 09/05/2018 01:55 AM, Tiwei Bie wrote:
> When VIRTIO_RING_F_EVENT_IDX is negotiated, we need to
> update the avail event to enable the notification.
> 
> Fixes: 3f8ff12821e4 ("vhost: support interrupt mode")
> Cc:stable@dpdk.org
> 
> Signed-off-by: Tiwei Bie<tiwei.bie@intel.com>
> ---
>   lib/librte_vhost/Makefile |  1 +
>   lib/librte_vhost/vhost.c  | 18 ++++++++++++------
>   lib/librte_vhost/vhost.h  |  2 ++
>   3 files changed, 15 insertions(+), 6 deletions(-)

Applied to dpdk-next-virtio/master.

Thanks!
Maxime

Re: [dpdk-dev] [dpdk-stable] [PATCH] vhost: fix vhost interrupt support

[Ferruh Yigit]

On 9/10/2018 8:36 AM, Tiwei Bie wrote:
> Hi Maxime,
> 
> On Mon, Sep 10, 2018 at 09:22:00AM +0200, Maxime Coquelin wrote:
>> Hi Tiwei,
>>
>> On 09/05/2018 01:55 AM, Tiwei Bie wrote:
>>> When VIRTIO_RING_F_EVENT_IDX is negotiated, we need to
>>> update the avail event to enable the notification.
>>>
>>> Fixes: 3f8ff12821e4 ("vhost: support interrupt mode")
>>> Cc: stable@dpdk.org
>>>
>>> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
>>> ---
>>>   lib/librte_vhost/Makefile |  1 +
>>>   lib/librte_vhost/vhost.c  | 18 ++++++++++++------
>>>   lib/librte_vhost/vhost.h  |  2 ++
>>>   3 files changed, 15 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/lib/librte_vhost/Makefile b/lib/librte_vhost/Makefile
>>> index de431fbb7..531cf4832 100644
>>> --- a/lib/librte_vhost/Makefile
>>> +++ b/lib/librte_vhost/Makefile
>>> @@ -13,6 +13,7 @@ LIBABIVER := 4
>>>   CFLAGS += -DALLOW_EXPERIMENTAL_API
>>>   CFLAGS += $(WERROR_FLAGS) -I$(SRCDIR) -O3 -D_FILE_OFFSET_BITS=64
>>>   CFLAGS += -I vhost_user
>>> +CFLAGS += -fno-strict-aliasing
>>
>> I'm not clear why this is needed looking at the code below,
>> could you please explain?
> 
> Without this, we will get below build error:
> 
> lib/librte_vhost/vhost.c: In function ‘vhost_enable_notify_split’:
> lib/librte_vhost/vhost.h:656:4: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
>   (*(volatile uint16_t*)&(vr)->used->ring[(vr)->size])
>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> lib/librte_vhost/vhost.c:659:4: note: in expansion of macro ‘vhost_avail_event’
>     vhost_avail_event(vq) = vq->last_avail_idx;
>     ^~~~~~~~~~~~~~~~~
> cc1: all warnings being treated as errors
> 

Getting this error with meson build system, since "-fno-strict-aliasing" is not
added to meson build file. BUT instead of disabling compiler warning,

first element of the "struct vring_used_elem ring[0]" is "uint32_t id;", so it
should be accessed as uint32_t. What about following:

  #define vhost_avail_event(vr) \
 -       (*(volatile uint16_t*)&(vr)->used->ring[(vr)->size])
 +       (*(volatile uint32_t*)&(vr)->used->ring[(vr)->size])

And for "vhost_avail_event(vq) = vq->last_avail_idx;", "last_avail_idx" is
uint16_t, so assigning from uint16_t to uint32_t should be ok too.

If above works for you please send a patch for update also removing
"-fno-strict-aliasing", this can be rebased on existing patch.

If not works, please at least send a patch to add flag to meson build file

Thanks,
ferruh

>>
>>>   LDLIBS += -lpthread
>>>   ifeq ($(CONFIG_RTE_LIBRTE_VHOST_NUMA),y)
>>> diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
>>> index 3c9be10a0..88b1781d5 100644
>>> --- a/lib/librte_vhost/vhost.c
>>> +++ b/lib/librte_vhost/vhost.c
>>> @@ -646,12 +646,18 @@ rte_vhost_avail_entries(int vid, uint16_t queue_id)
>>>   }
>>>   static inline void
>>> -vhost_enable_notify_split(struct vhost_virtqueue *vq, int enable)
>>> +vhost_enable_notify_split(struct virtio_net *dev,
>>> +		struct vhost_virtqueue *vq, int enable)
>>>   {
>>> -	if (enable)
>>> -		vq->used->flags &= ~VRING_USED_F_NO_NOTIFY;
>>> -	else
>>> -		vq->used->flags |= VRING_USED_F_NO_NOTIFY;
>>> +	if (!(dev->features & (1ULL << VIRTIO_RING_F_EVENT_IDX))) {
>>> +		if (enable)
>>> +			vq->used->flags &= ~VRING_USED_F_NO_NOTIFY;
>>> +		else
>>> +			vq->used->flags |= VRING_USED_F_NO_NOTIFY;
>>> +	} else {
>>> +		if (enable)
>>> +			vhost_avail_event(vq) = vq->last_avail_idx;
>>> +	}
>>>   }
>>>   static inline void
>>> @@ -689,7 +695,7 @@ rte_vhost_enable_guest_notification(int vid, uint16_t queue_id, int enable)
>>>   	if (vq_is_packed(dev))
>>>   		vhost_enable_notify_packed(dev, vq, enable);
>>>   	else
>>> -		vhost_enable_notify_split(vq, enable);
>>> +		vhost_enable_notify_split(dev, vq, enable);
>>>   	return 0;
>>>   }
>>> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
>>> index 760a09c0d..25ffd7614 100644
>>> --- a/lib/librte_vhost/vhost.h
>>> +++ b/lib/librte_vhost/vhost.h
>>> @@ -648,6 +648,8 @@ vhost_iova_to_vva(struct virtio_net *dev, struct vhost_virtqueue *vq,
>>>   	return __vhost_iova_to_vva(dev, vq, iova, len, perm);
>>>   }
>>> +#define vhost_avail_event(vr) \
>>> +	(*(volatile uint16_t*)&(vr)->used->ring[(vr)->size])
>>>   #define vhost_used_event(vr) \
>>>   	(*(volatile uint16_t*)&(vr)->avail->ring[(vr)->size])
>>>

Re: [dpdk-dev] [dpdk-stable] [PATCH] vhost: fix vhost interrupt support

[Tiwei Bie]

On Fri, Sep 14, 2018 at 01:10:07PM +0100, Ferruh Yigit wrote:
> On 9/10/2018 8:36 AM, Tiwei Bie wrote:
> > Hi Maxime,
> > 
> > On Mon, Sep 10, 2018 at 09:22:00AM +0200, Maxime Coquelin wrote:
> >> Hi Tiwei,
> >>
> >> On 09/05/2018 01:55 AM, Tiwei Bie wrote:
> >>> When VIRTIO_RING_F_EVENT_IDX is negotiated, we need to
> >>> update the avail event to enable the notification.
> >>>
> >>> Fixes: 3f8ff12821e4 ("vhost: support interrupt mode")
> >>> Cc: stable@dpdk.org
> >>>
> >>> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
> >>> ---
> >>>   lib/librte_vhost/Makefile |  1 +
> >>>   lib/librte_vhost/vhost.c  | 18 ++++++++++++------
> >>>   lib/librte_vhost/vhost.h  |  2 ++
> >>>   3 files changed, 15 insertions(+), 6 deletions(-)
> >>>
> >>> diff --git a/lib/librte_vhost/Makefile b/lib/librte_vhost/Makefile
> >>> index de431fbb7..531cf4832 100644
> >>> --- a/lib/librte_vhost/Makefile
> >>> +++ b/lib/librte_vhost/Makefile
> >>> @@ -13,6 +13,7 @@ LIBABIVER := 4
> >>>   CFLAGS += -DALLOW_EXPERIMENTAL_API
> >>>   CFLAGS += $(WERROR_FLAGS) -I$(SRCDIR) -O3 -D_FILE_OFFSET_BITS=64
> >>>   CFLAGS += -I vhost_user
> >>> +CFLAGS += -fno-strict-aliasing
> >>
> >> I'm not clear why this is needed looking at the code below,
> >> could you please explain?
> > 
> > Without this, we will get below build error:
> > 
> > lib/librte_vhost/vhost.c: In function ‘vhost_enable_notify_split’:
> > lib/librte_vhost/vhost.h:656:4: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
> >   (*(volatile uint16_t*)&(vr)->used->ring[(vr)->size])
> >     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > lib/librte_vhost/vhost.c:659:4: note: in expansion of macro ‘vhost_avail_event’
> >     vhost_avail_event(vq) = vq->last_avail_idx;
> >     ^~~~~~~~~~~~~~~~~
> > cc1: all warnings being treated as errors
> > 
> 
> Getting this error with meson build system, since "-fno-strict-aliasing" is not
> added to meson build file.

Thanks! I didn't notice this. I just tried the meson build manually.
The warning isn't treated as errors on my side. So it was not caught
by the build script..

> BUT instead of disabling compiler warning,
> 
> first element of the "struct vring_used_elem ring[0]" is "uint32_t id;", so it
> should be accessed as uint32_t. What about following:
> 
>   #define vhost_avail_event(vr) \
>  -       (*(volatile uint16_t*)&(vr)->used->ring[(vr)->size])
>  +       (*(volatile uint32_t*)&(vr)->used->ring[(vr)->size])
> 
> And for "vhost_avail_event(vq) = vq->last_avail_idx;", "last_avail_idx" is
> uint16_t, so assigning from uint16_t to uint32_t should be ok too.

At the end of used ring, there is a 16bits event_idx. It can't
be interpreted as a vring_used_elem and it's also not part of a
vring_used_elem. This is the traditional way how we access it:

https://github.com/torvalds/linux/blob/a06b0c82a049/drivers/vhost/vhost.c#L50
https://github.com/freebsd/freebsd/blob/209b94df8701/sys/dev/virtio/virtio_ring.h#L133

> 
> If above works for you please send a patch for update also removing
> "-fno-strict-aliasing", this can be rebased on existing patch.
> 
> If not works, please at least send a patch to add flag to meson build file

I'll send a patch to add flag to meson build file.

Thanks!

> 
> Thanks,
> ferruh
> 
> >>
> >>>   LDLIBS += -lpthread
> >>>   ifeq ($(CONFIG_RTE_LIBRTE_VHOST_NUMA),y)
> >>> diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
> >>> index 3c9be10a0..88b1781d5 100644
> >>> --- a/lib/librte_vhost/vhost.c
> >>> +++ b/lib/librte_vhost/vhost.c
> >>> @@ -646,12 +646,18 @@ rte_vhost_avail_entries(int vid, uint16_t queue_id)
> >>>   }
> >>>   static inline void
> >>> -vhost_enable_notify_split(struct vhost_virtqueue *vq, int enable)
> >>> +vhost_enable_notify_split(struct virtio_net *dev,
> >>> +		struct vhost_virtqueue *vq, int enable)
> >>>   {
> >>> -	if (enable)
> >>> -		vq->used->flags &= ~VRING_USED_F_NO_NOTIFY;
> >>> -	else
> >>> -		vq->used->flags |= VRING_USED_F_NO_NOTIFY;
> >>> +	if (!(dev->features & (1ULL << VIRTIO_RING_F_EVENT_IDX))) {
> >>> +		if (enable)
> >>> +			vq->used->flags &= ~VRING_USED_F_NO_NOTIFY;
> >>> +		else
> >>> +			vq->used->flags |= VRING_USED_F_NO_NOTIFY;
> >>> +	} else {
> >>> +		if (enable)
> >>> +			vhost_avail_event(vq) = vq->last_avail_idx;
> >>> +	}
> >>>   }
> >>>   static inline void
> >>> @@ -689,7 +695,7 @@ rte_vhost_enable_guest_notification(int vid, uint16_t queue_id, int enable)
> >>>   	if (vq_is_packed(dev))
> >>>   		vhost_enable_notify_packed(dev, vq, enable);
> >>>   	else
> >>> -		vhost_enable_notify_split(vq, enable);
> >>> +		vhost_enable_notify_split(dev, vq, enable);
> >>>   	return 0;
> >>>   }
> >>> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> >>> index 760a09c0d..25ffd7614 100644
> >>> --- a/lib/librte_vhost/vhost.h
> >>> +++ b/lib/librte_vhost/vhost.h
> >>> @@ -648,6 +648,8 @@ vhost_iova_to_vva(struct virtio_net *dev, struct vhost_virtqueue *vq,
> >>>   	return __vhost_iova_to_vva(dev, vq, iova, len, perm);
> >>>   }
> >>> +#define vhost_avail_event(vr) \
> >>> +	(*(volatile uint16_t*)&(vr)->used->ring[(vr)->size])
> >>>   #define vhost_used_event(vr) \
> >>>   	(*(volatile uint16_t*)&(vr)->avail->ring[(vr)->size])
> >>>
>