[PATCH] virtio_ring: use u32 for virtio_max_dma_size

[PATCH] virtio_ring: use u32 for virtio_max_dma_size

[zhenwei pi via Virtualization]

Both split ring and packed ring use 32bits to describe the length of
a descriptor: see struct vring_desc and struct vring_packed_desc.
This means the max segment size supported by virtio is U32_MAX.

An example of virtio_max_dma_size in virtio_blk.c:
  u32 v, max_size;

  max_size = virtio_max_dma_size(vdev);  -> implicit convert
  err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SIZE_MAX,
                             struct virtio_blk_config, size_max, &v);
  max_size = min(max_size, v);

There is a risk during implicit convert here, once virtio_max_dma_size
returns 4G, max_size becomes 0.

Fixes: e6d6dd6c875e ("virtio: Introduce virtio_max_dma_size()")
Cc: Joerg Roedel <jroedel@suse.de>
Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
---
 drivers/virtio/virtio_ring.c | 12 ++++++++----
 include/linux/virtio.h       |  2 +-
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index c5310eaf8b46..55cfecf030a1 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -289,12 +289,16 @@ static bool vring_use_dma_api(const struct virtio_device *vdev)
 	return false;
 }
 
-size_t virtio_max_dma_size(const struct virtio_device *vdev)
+u32 virtio_max_dma_size(const struct virtio_device *vdev)
 {
-	size_t max_segment_size = SIZE_MAX;
+	u32 max_segment_size = U32_MAX;
 
-	if (vring_use_dma_api(vdev))
-		max_segment_size = dma_max_mapping_size(vdev->dev.parent);
+	if (vring_use_dma_api(vdev)) {
+		size_t max_dma_size = dma_max_mapping_size(vdev->dev.parent);
+
+		if (max_dma_size < max_segment_size)
+			max_segment_size = max_dma_size;
+	}
 
 	return max_segment_size;
 }
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index b93238db94e3..1a605f408329 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -147,7 +147,7 @@ int virtio_device_restore(struct virtio_device *dev);
 #endif
 void virtio_reset_device(struct virtio_device *dev);
 
-size_t virtio_max_dma_size(const struct virtio_device *vdev);
+u32 virtio_max_dma_size(const struct virtio_device *vdev);
 
 #define virtio_device_for_each_vq(vdev, vq) \
 	list_for_each_entry(vq, &vdev->vqs, list)
-- 
2.20.1

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Re: [PATCH] virtio_ring: use u32 for virtio_max_dma_size

[Xuan Zhuo]

On Wed, 10 May 2023 10:54:37 +0800, zhenwei pi <pizhenwei@bytedance.com> wrote:
> Both split ring and packed ring use 32bits to describe the length of
> a descriptor: see struct vring_desc and struct vring_packed_desc.
> This means the max segment size supported by virtio is U32_MAX.
>
> An example of virtio_max_dma_size in virtio_blk.c:
>   u32 v, max_size;
>
>   max_size = virtio_max_dma_size(vdev);  -> implicit convert
>   err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SIZE_MAX,
>                              struct virtio_blk_config, size_max, &v);
>   max_size = min(max_size, v);
>
> There is a risk during implicit convert here, once virtio_max_dma_size
> returns 4G, max_size becomes 0.
>
> Fixes: e6d6dd6c875e ("virtio: Introduce virtio_max_dma_size()")
> Cc: Joerg Roedel <jroedel@suse.de>
> Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
> ---
>  drivers/virtio/virtio_ring.c | 12 ++++++++----
>  include/linux/virtio.h       |  2 +-
>  2 files changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index c5310eaf8b46..55cfecf030a1 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -289,12 +289,16 @@ static bool vring_use_dma_api(const struct virtio_device *vdev)
>  	return false;
>  }
>
> -size_t virtio_max_dma_size(const struct virtio_device *vdev)
> +u32 virtio_max_dma_size(const struct virtio_device *vdev)


LGTM

But, should we change the parameter to vq, then use the dma_dev?

@Jason

Thanks.


>  {
> -	size_t max_segment_size = SIZE_MAX;
> +	u32 max_segment_size = U32_MAX;
>
> -	if (vring_use_dma_api(vdev))
> -		max_segment_size = dma_max_mapping_size(vdev->dev.parent);
> +	if (vring_use_dma_api(vdev)) {
> +		size_t max_dma_size = dma_max_mapping_size(vdev->dev.parent);
> +
> +		if (max_dma_size < max_segment_size)
> +			max_segment_size = max_dma_size;
> +	}
>
>  	return max_segment_size;
>  }
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index b93238db94e3..1a605f408329 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -147,7 +147,7 @@ int virtio_device_restore(struct virtio_device *dev);
>  #endif
>  void virtio_reset_device(struct virtio_device *dev);
>
> -size_t virtio_max_dma_size(const struct virtio_device *vdev);
> +u32 virtio_max_dma_size(const struct virtio_device *vdev);
>
>  #define virtio_device_for_each_vq(vdev, vq) \
>  	list_for_each_entry(vq, &vdev->vqs, list)
> --
> 2.20.1
>
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Re: [PATCH] virtio_ring: use u32 for virtio_max_dma_size

[Michael S. Tsirkin]

On Wed, May 10, 2023 at 11:26:54AM +0800, Xuan Zhuo wrote:
> On Wed, 10 May 2023 10:54:37 +0800, zhenwei pi <pizhenwei@bytedance.com> wrote:
> > Both split ring and packed ring use 32bits to describe the length of
> > a descriptor: see struct vring_desc and struct vring_packed_desc.
> > This means the max segment size supported by virtio is U32_MAX.
> >
> > An example of virtio_max_dma_size in virtio_blk.c:
> >   u32 v, max_size;
> >
> >   max_size = virtio_max_dma_size(vdev);  -> implicit convert
> >   err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SIZE_MAX,
> >                              struct virtio_blk_config, size_max, &v);
> >   max_size = min(max_size, v);
> >
> > There is a risk during implicit convert here, once virtio_max_dma_size
> > returns 4G, max_size becomes 0.
> >
> > Fixes: e6d6dd6c875e ("virtio: Introduce virtio_max_dma_size()")
> > Cc: Joerg Roedel <jroedel@suse.de>
> > Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
> > ---
> >  drivers/virtio/virtio_ring.c | 12 ++++++++----
> >  include/linux/virtio.h       |  2 +-
> >  2 files changed, 9 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index c5310eaf8b46..55cfecf030a1 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -289,12 +289,16 @@ static bool vring_use_dma_api(const struct virtio_device *vdev)
> >  	return false;
> >  }
> >
> > -size_t virtio_max_dma_size(const struct virtio_device *vdev)
> > +u32 virtio_max_dma_size(const struct virtio_device *vdev)
> 
> 
> LGTM
> 
> But, should we change the parameter to vq, then use the dma_dev?
> 
> @Jason
> 
> Thanks.
> 


that would be an unrelated rework.

> >  {
> > -	size_t max_segment_size = SIZE_MAX;
> > +	u32 max_segment_size = U32_MAX;
> >
> > -	if (vring_use_dma_api(vdev))
> > -		max_segment_size = dma_max_mapping_size(vdev->dev.parent);
> > +	if (vring_use_dma_api(vdev)) {
> > +		size_t max_dma_size = dma_max_mapping_size(vdev->dev.parent);
> > +
> > +		if (max_dma_size < max_segment_size)
> > +			max_segment_size = max_dma_size;
> > +	}
> >
> >  	return max_segment_size;
> >  }
> > diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> > index b93238db94e3..1a605f408329 100644
> > --- a/include/linux/virtio.h
> > +++ b/include/linux/virtio.h
> > @@ -147,7 +147,7 @@ int virtio_device_restore(struct virtio_device *dev);
> >  #endif
> >  void virtio_reset_device(struct virtio_device *dev);
> >
> > -size_t virtio_max_dma_size(const struct virtio_device *vdev);
> > +u32 virtio_max_dma_size(const struct virtio_device *vdev);
> >
> >  #define virtio_device_for_each_vq(vdev, vq) \
> >  	list_for_each_entry(vq, &vdev->vqs, list)
> > --
> > 2.20.1
> >

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Re: [PATCH] virtio_ring: use u32 for virtio_max_dma_size

[Jason Wang]

On Wed, May 10, 2023 at 11:44 AM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Wed, May 10, 2023 at 11:26:54AM +0800, Xuan Zhuo wrote:
> > On Wed, 10 May 2023 10:54:37 +0800, zhenwei pi <pizhenwei@bytedance.com> wrote:
> > > Both split ring and packed ring use 32bits to describe the length of
> > > a descriptor: see struct vring_desc and struct vring_packed_desc.
> > > This means the max segment size supported by virtio is U32_MAX.
> > >
> > > An example of virtio_max_dma_size in virtio_blk.c:
> > >   u32 v, max_size;
> > >
> > >   max_size = virtio_max_dma_size(vdev);  -> implicit convert
> > >   err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SIZE_MAX,
> > >                              struct virtio_blk_config, size_max, &v);
> > >   max_size = min(max_size, v);
> > >
> > > There is a risk during implicit convert here, once virtio_max_dma_size
> > > returns 4G, max_size becomes 0.
> > >
> > > Fixes: e6d6dd6c875e ("virtio: Introduce virtio_max_dma_size()")
> > > Cc: Joerg Roedel <jroedel@suse.de>
> > > Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
> > > ---
> > >  drivers/virtio/virtio_ring.c | 12 ++++++++----
> > >  include/linux/virtio.h       |  2 +-
> > >  2 files changed, 9 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > > index c5310eaf8b46..55cfecf030a1 100644
> > > --- a/drivers/virtio/virtio_ring.c
> > > +++ b/drivers/virtio/virtio_ring.c
> > > @@ -289,12 +289,16 @@ static bool vring_use_dma_api(const struct virtio_device *vdev)
> > >     return false;
> > >  }
> > >
> > > -size_t virtio_max_dma_size(const struct virtio_device *vdev)
> > > +u32 virtio_max_dma_size(const struct virtio_device *vdev)
> >
> >
> > LGTM
> >
> > But, should we change the parameter to vq, then use the dma_dev?
> >
> > @Jason
> >
> > Thanks.
> >
>
>
> that would be an unrelated rework.

Probably, but I think it's better to be done on top otherwise we may forget.

Thanks

>
> > >  {
> > > -   size_t max_segment_size = SIZE_MAX;
> > > +   u32 max_segment_size = U32_MAX;
> > >
> > > -   if (vring_use_dma_api(vdev))
> > > -           max_segment_size = dma_max_mapping_size(vdev->dev.parent);
> > > +   if (vring_use_dma_api(vdev)) {
> > > +           size_t max_dma_size = dma_max_mapping_size(vdev->dev.parent);
> > > +
> > > +           if (max_dma_size < max_segment_size)
> > > +                   max_segment_size = max_dma_size;
> > > +   }
> > >
> > >     return max_segment_size;
> > >  }
> > > diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> > > index b93238db94e3..1a605f408329 100644
> > > --- a/include/linux/virtio.h
> > > +++ b/include/linux/virtio.h
> > > @@ -147,7 +147,7 @@ int virtio_device_restore(struct virtio_device *dev);
> > >  #endif
> > >  void virtio_reset_device(struct virtio_device *dev);
> > >
> > > -size_t virtio_max_dma_size(const struct virtio_device *vdev);
> > > +u32 virtio_max_dma_size(const struct virtio_device *vdev);
> > >
> > >  #define virtio_device_for_each_vq(vdev, vq) \
> > >     list_for_each_entry(vq, &vdev->vqs, list)
> > > --
> > > 2.20.1
> > >
>

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Re: [PATCH] virtio_ring: use u32 for virtio_max_dma_size

[Michael S. Tsirkin]

On Wed, May 10, 2023 at 12:04:50PM +0800, Jason Wang wrote:
> On Wed, May 10, 2023 at 11:44 AM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Wed, May 10, 2023 at 11:26:54AM +0800, Xuan Zhuo wrote:
> > > On Wed, 10 May 2023 10:54:37 +0800, zhenwei pi <pizhenwei@bytedance.com> wrote:
> > > > Both split ring and packed ring use 32bits to describe the length of
> > > > a descriptor: see struct vring_desc and struct vring_packed_desc.
> > > > This means the max segment size supported by virtio is U32_MAX.
> > > >
> > > > An example of virtio_max_dma_size in virtio_blk.c:
> > > >   u32 v, max_size;
> > > >
> > > >   max_size = virtio_max_dma_size(vdev);  -> implicit convert
> > > >   err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SIZE_MAX,
> > > >                              struct virtio_blk_config, size_max, &v);
> > > >   max_size = min(max_size, v);
> > > >
> > > > There is a risk during implicit convert here, once virtio_max_dma_size
> > > > returns 4G, max_size becomes 0.
> > > >
> > > > Fixes: e6d6dd6c875e ("virtio: Introduce virtio_max_dma_size()")
> > > > Cc: Joerg Roedel <jroedel@suse.de>
> > > > Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
> > > > ---
> > > >  drivers/virtio/virtio_ring.c | 12 ++++++++----
> > > >  include/linux/virtio.h       |  2 +-
> > > >  2 files changed, 9 insertions(+), 5 deletions(-)
> > > >
> > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > > > index c5310eaf8b46..55cfecf030a1 100644
> > > > --- a/drivers/virtio/virtio_ring.c
> > > > +++ b/drivers/virtio/virtio_ring.c
> > > > @@ -289,12 +289,16 @@ static bool vring_use_dma_api(const struct virtio_device *vdev)
> > > >     return false;
> > > >  }
> > > >
> > > > -size_t virtio_max_dma_size(const struct virtio_device *vdev)
> > > > +u32 virtio_max_dma_size(const struct virtio_device *vdev)
> > >
> > >
> > > LGTM
> > >
> > > But, should we change the parameter to vq, then use the dma_dev?
> > >
> > > @Jason
> > >
> > > Thanks.
> > >
> >
> >
> > that would be an unrelated rework.
> 
> Probably, but I think it's better to be done on top otherwise we may forget.
> 
> Thanks

Just to make things clear I'm merging fixes for this
release but cleanups belong in the next one.

> >
> > > >  {
> > > > -   size_t max_segment_size = SIZE_MAX;
> > > > +   u32 max_segment_size = U32_MAX;
> > > >
> > > > -   if (vring_use_dma_api(vdev))
> > > > -           max_segment_size = dma_max_mapping_size(vdev->dev.parent);
> > > > +   if (vring_use_dma_api(vdev)) {
> > > > +           size_t max_dma_size = dma_max_mapping_size(vdev->dev.parent);
> > > > +
> > > > +           if (max_dma_size < max_segment_size)
> > > > +                   max_segment_size = max_dma_size;
> > > > +   }
> > > >
> > > >     return max_segment_size;
> > > >  }
> > > > diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> > > > index b93238db94e3..1a605f408329 100644
> > > > --- a/include/linux/virtio.h
> > > > +++ b/include/linux/virtio.h
> > > > @@ -147,7 +147,7 @@ int virtio_device_restore(struct virtio_device *dev);
> > > >  #endif
> > > >  void virtio_reset_device(struct virtio_device *dev);
> > > >
> > > > -size_t virtio_max_dma_size(const struct virtio_device *vdev);
> > > > +u32 virtio_max_dma_size(const struct virtio_device *vdev);
> > > >
> > > >  #define virtio_device_for_each_vq(vdev, vq) \
> > > >     list_for_each_entry(vq, &vdev->vqs, list)
> > > > --
> > > > 2.20.1
> > > >
> >

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PING Re: [PATCH] virtio_ring: use u32 for virtio_max_dma_size

[zhenwei pi via Virtualization]

Hi Michael,

This seems to be ignored...

On 5/10/23 12:06, Michael S. Tsirkin wrote:
> On Wed, May 10, 2023 at 12:04:50PM +0800, Jason Wang wrote:
>> On Wed, May 10, 2023 at 11:44 AM Michael S. Tsirkin <mst@redhat.com> wrote:
>>>
>>> On Wed, May 10, 2023 at 11:26:54AM +0800, Xuan Zhuo wrote:
>>>> On Wed, 10 May 2023 10:54:37 +0800, zhenwei pi <pizhenwei@bytedance.com> wrote:
>>>>> Both split ring and packed ring use 32bits to describe the length of
>>>>> a descriptor: see struct vring_desc and struct vring_packed_desc.
>>>>> This means the max segment size supported by virtio is U32_MAX.
>>>>>
>>>>> An example of virtio_max_dma_size in virtio_blk.c:
>>>>>    u32 v, max_size;
>>>>>
>>>>>    max_size = virtio_max_dma_size(vdev);  -> implicit convert
>>>>>    err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SIZE_MAX,
>>>>>                               struct virtio_blk_config, size_max, &v);
>>>>>    max_size = min(max_size, v);
>>>>>
>>>>> There is a risk during implicit convert here, once virtio_max_dma_size
>>>>> returns 4G, max_size becomes 0.
>>>>>
>>>>> Fixes: e6d6dd6c875e ("virtio: Introduce virtio_max_dma_size()")
>>>>> Cc: Joerg Roedel <jroedel@suse.de>
>>>>> Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
>>>>> ---
>>>>>   drivers/virtio/virtio_ring.c | 12 ++++++++----
>>>>>   include/linux/virtio.h       |  2 +-
>>>>>   2 files changed, 9 insertions(+), 5 deletions(-)
>>>>>
>>>>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
>>>>> index c5310eaf8b46..55cfecf030a1 100644
>>>>> --- a/drivers/virtio/virtio_ring.c
>>>>> +++ b/drivers/virtio/virtio_ring.c
>>>>> @@ -289,12 +289,16 @@ static bool vring_use_dma_api(const struct virtio_device *vdev)
>>>>>      return false;
>>>>>   }
>>>>>
>>>>> -size_t virtio_max_dma_size(const struct virtio_device *vdev)
>>>>> +u32 virtio_max_dma_size(const struct virtio_device *vdev)
>>>>
>>>>
>>>> LGTM
>>>>
>>>> But, should we change the parameter to vq, then use the dma_dev?
>>>>
>>>> @Jason
>>>>
>>>> Thanks.
>>>>
>>>
>>>
>>> that would be an unrelated rework.
>>
>> Probably, but I think it's better to be done on top otherwise we may forget.
>>
>> Thanks
> 
> Just to make things clear I'm merging fixes for this
> release but cleanups belong in the next one.
> 
>>>
>>>>>   {
>>>>> -   size_t max_segment_size = SIZE_MAX;
>>>>> +   u32 max_segment_size = U32_MAX;
>>>>>
>>>>> -   if (vring_use_dma_api(vdev))
>>>>> -           max_segment_size = dma_max_mapping_size(vdev->dev.parent);
>>>>> +   if (vring_use_dma_api(vdev)) {
>>>>> +           size_t max_dma_size = dma_max_mapping_size(vdev->dev.parent);
>>>>> +
>>>>> +           if (max_dma_size < max_segment_size)
>>>>> +                   max_segment_size = max_dma_size;
>>>>> +   }
>>>>>
>>>>>      return max_segment_size;
>>>>>   }
>>>>> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
>>>>> index b93238db94e3..1a605f408329 100644
>>>>> --- a/include/linux/virtio.h
>>>>> +++ b/include/linux/virtio.h
>>>>> @@ -147,7 +147,7 @@ int virtio_device_restore(struct virtio_device *dev);
>>>>>   #endif
>>>>>   void virtio_reset_device(struct virtio_device *dev);
>>>>>
>>>>> -size_t virtio_max_dma_size(const struct virtio_device *vdev);
>>>>> +u32 virtio_max_dma_size(const struct virtio_device *vdev);
>>>>>
>>>>>   #define virtio_device_for_each_vq(vdev, vq) \
>>>>>      list_for_each_entry(vq, &vdev->vqs, list)
>>>>> --
>>>>> 2.20.1
>>>>>
>>>
> 

-- 
zhenwei pi
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Re: Re: [PATCH] virtio_ring: use u32 for virtio_max_dma_size

[zhenwei pi via Virtualization]

On 5/10/23 11:26, Xuan Zhuo wrote:
> On Wed, 10 May 2023 10:54:37 +0800, zhenwei pi <pizhenwei@bytedance.com> wrote:
>> Both split ring and packed ring use 32bits to describe the length of
>> a descriptor: see struct vring_desc and struct vring_packed_desc.
>> This means the max segment size supported by virtio is U32_MAX.
>>
>> An example of virtio_max_dma_size in virtio_blk.c:
>>    u32 v, max_size;
>>
>>    max_size = virtio_max_dma_size(vdev);  -> implicit convert
>>    err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SIZE_MAX,
>>                               struct virtio_blk_config, size_max, &v);
>>    max_size = min(max_size, v);
>>
>> There is a risk during implicit convert here, once virtio_max_dma_size
>> returns 4G, max_size becomes 0.
>>
>> Fixes: e6d6dd6c875e ("virtio: Introduce virtio_max_dma_size()")
>> Cc: Joerg Roedel <jroedel@suse.de>
>> Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
>> ---
>>   drivers/virtio/virtio_ring.c | 12 ++++++++----
>>   include/linux/virtio.h       |  2 +-
>>   2 files changed, 9 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
>> index c5310eaf8b46..55cfecf030a1 100644
>> --- a/drivers/virtio/virtio_ring.c
>> +++ b/drivers/virtio/virtio_ring.c
>> @@ -289,12 +289,16 @@ static bool vring_use_dma_api(const struct virtio_device *vdev)
>>   	return false;
>>   }
>>
>> -size_t virtio_max_dma_size(const struct virtio_device *vdev)
>> +u32 virtio_max_dma_size(const struct virtio_device *vdev)
> 
> 
> LGTM
> 
> But, should we change the parameter to vq, then use the dma_dev?
> 
> @Jason
> 
> Thanks.
> 

The max DMA size is a attribute of a virtio device rather than any VQ, 
so I guess virtio_max_dma_size(const struct virtio_device *vdev) is clear.

On the other hand, if changing the parameter to vq, we need select a VQ, 
then the question is:
1, which VQ to select? VQ0 or a random one? this leads confusing.
2, The virtio spec defines: Each device can have zero or more virtqueues


> 
>>   {
>> -	size_t max_segment_size = SIZE_MAX;
>> +	u32 max_segment_size = U32_MAX;
>>
>> -	if (vring_use_dma_api(vdev))
>> -		max_segment_size = dma_max_mapping_size(vdev->dev.parent);
>> +	if (vring_use_dma_api(vdev)) {
>> +		size_t max_dma_size = dma_max_mapping_size(vdev->dev.parent);
>> +
>> +		if (max_dma_size < max_segment_size)
>> +			max_segment_size = max_dma_size;
>> +	}
>>
>>   	return max_segment_size;
>>   }
>> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
>> index b93238db94e3..1a605f408329 100644
>> --- a/include/linux/virtio.h
>> +++ b/include/linux/virtio.h
>> @@ -147,7 +147,7 @@ int virtio_device_restore(struct virtio_device *dev);
>>   #endif
>>   void virtio_reset_device(struct virtio_device *dev);
>>
>> -size_t virtio_max_dma_size(const struct virtio_device *vdev);
>> +u32 virtio_max_dma_size(const struct virtio_device *vdev);
>>
>>   #define virtio_device_for_each_vq(vdev, vq) \
>>   	list_for_each_entry(vq, &vdev->vqs, list)
>> --
>> 2.20.1
>>

-- 
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Re: [PATCH] virtio_ring: use u32 for virtio_max_dma_size

[Michael S. Tsirkin]

On Wed, May 10, 2023 at 10:54:37AM +0800, zhenwei pi wrote:
> Both split ring and packed ring use 32bits to describe the length of
> a descriptor: see struct vring_desc and struct vring_packed_desc.
> This means the max segment size supported by virtio is U32_MAX.
> 
> An example of virtio_max_dma_size in virtio_blk.c:
>   u32 v, max_size;
> 
>   max_size = virtio_max_dma_size(vdev);  -> implicit convert
>   err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SIZE_MAX,
>                              struct virtio_blk_config, size_max, &v);
>   max_size = min(max_size, v);
> 
> There is a risk during implicit convert here, once virtio_max_dma_size
> returns 4G, max_size becomes 0.
> 
> Fixes: e6d6dd6c875e ("virtio: Introduce virtio_max_dma_size()")
> Cc: Joerg Roedel <jroedel@suse.de>
> Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>


is this a theoretical concern or do you manage to trigger this
somehow?

> ---
>  drivers/virtio/virtio_ring.c | 12 ++++++++----
>  include/linux/virtio.h       |  2 +-
>  2 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index c5310eaf8b46..55cfecf030a1 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -289,12 +289,16 @@ static bool vring_use_dma_api(const struct virtio_device *vdev)
>  	return false;
>  }
>  
> -size_t virtio_max_dma_size(const struct virtio_device *vdev)
> +u32 virtio_max_dma_size(const struct virtio_device *vdev)
>  {
> -	size_t max_segment_size = SIZE_MAX;
> +	u32 max_segment_size = U32_MAX;
>  
> -	if (vring_use_dma_api(vdev))
> -		max_segment_size = dma_max_mapping_size(vdev->dev.parent);
> +	if (vring_use_dma_api(vdev)) {
> +		size_t max_dma_size = dma_max_mapping_size(vdev->dev.parent);
> +
> +		if (max_dma_size < max_segment_size)
> +			max_segment_size = max_dma_size;
> +	}
>  
>  	return max_segment_size;
>  }
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index b93238db94e3..1a605f408329 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -147,7 +147,7 @@ int virtio_device_restore(struct virtio_device *dev);
>  #endif
>  void virtio_reset_device(struct virtio_device *dev);
>  
> -size_t virtio_max_dma_size(const struct virtio_device *vdev);
> +u32 virtio_max_dma_size(const struct virtio_device *vdev);
>  
>  #define virtio_device_for_each_vq(vdev, vq) \
>  	list_for_each_entry(vq, &vdev->vqs, list)
> -- 
> 2.20.1

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Re: Re: [PATCH] virtio_ring: use u32 for virtio_max_dma_size

[zhenwei pi via Virtualization]

On 5/10/23 11:39, Michael S. Tsirkin wrote:
> On Wed, May 10, 2023 at 10:54:37AM +0800, zhenwei pi wrote:
>> Both split ring and packed ring use 32bits to describe the length of
>> a descriptor: see struct vring_desc and struct vring_packed_desc.
>> This means the max segment size supported by virtio is U32_MAX.
>>
>> An example of virtio_max_dma_size in virtio_blk.c:
>>    u32 v, max_size;
>>
>>    max_size = virtio_max_dma_size(vdev);  -> implicit convert
>>    err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SIZE_MAX,
>>                               struct virtio_blk_config, size_max, &v);
>>    max_size = min(max_size, v);
>>
>> There is a risk during implicit convert here, once virtio_max_dma_size
>> returns 4G, max_size becomes 0.
>>
>> Fixes: e6d6dd6c875e ("virtio: Introduce virtio_max_dma_size()")
>> Cc: Joerg Roedel <jroedel@suse.de>
>> Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
> 
> 
> is this a theoretical concern or do you manage to trigger this
> somehow?
> 

I never hit any issue about this, I notice here during diving into the 
symbols exported by virtio_ring.ko.

>> ---
>>   drivers/virtio/virtio_ring.c | 12 ++++++++----
>>   include/linux/virtio.h       |  2 +-
>>   2 files changed, 9 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
>> index c5310eaf8b46..55cfecf030a1 100644
>> --- a/drivers/virtio/virtio_ring.c
>> +++ b/drivers/virtio/virtio_ring.c
>> @@ -289,12 +289,16 @@ static bool vring_use_dma_api(const struct virtio_device *vdev)
>>   	return false;
>>   }
>>   
>> -size_t virtio_max_dma_size(const struct virtio_device *vdev)
>> +u32 virtio_max_dma_size(const struct virtio_device *vdev)
>>   {
>> -	size_t max_segment_size = SIZE_MAX;
>> +	u32 max_segment_size = U32_MAX;
>>   
>> -	if (vring_use_dma_api(vdev))
>> -		max_segment_size = dma_max_mapping_size(vdev->dev.parent);
>> +	if (vring_use_dma_api(vdev)) {
>> +		size_t max_dma_size = dma_max_mapping_size(vdev->dev.parent);
>> +
>> +		if (max_dma_size < max_segment_size)
>> +			max_segment_size = max_dma_size;
>> +	}
>>   
>>   	return max_segment_size;
>>   }
>> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
>> index b93238db94e3..1a605f408329 100644
>> --- a/include/linux/virtio.h
>> +++ b/include/linux/virtio.h
>> @@ -147,7 +147,7 @@ int virtio_device_restore(struct virtio_device *dev);
>>   #endif
>>   void virtio_reset_device(struct virtio_device *dev);
>>   
>> -size_t virtio_max_dma_size(const struct virtio_device *vdev);
>> +u32 virtio_max_dma_size(const struct virtio_device *vdev);
>>   
>>   #define virtio_device_for_each_vq(vdev, vq) \
>>   	list_for_each_entry(vq, &vdev->vqs, list)
>> -- 
>> 2.20.1
> 

-- 
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Re: [PATCH] virtio_ring: use u32 for virtio_max_dma_size

[Michael S. Tsirkin]

On Wed, May 10, 2023 at 10:54:37AM +0800, zhenwei pi wrote:
> Both split ring and packed ring use 32bits to describe the length of
> a descriptor: see struct vring_desc and struct vring_packed_desc.
> This means the max segment size supported by virtio is U32_MAX.
> 
> An example of virtio_max_dma_size in virtio_blk.c:
>   u32 v, max_size;
> 
>   max_size = virtio_max_dma_size(vdev);  -> implicit convert
>   err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SIZE_MAX,
>                              struct virtio_blk_config, size_max, &v);
>   max_size = min(max_size, v);
> 
> There is a risk during implicit convert here, once virtio_max_dma_size
> returns 4G, max_size becomes 0.
> 
> Fixes: e6d6dd6c875e ("virtio: Introduce virtio_max_dma_size()")
> Cc: Joerg Roedel <jroedel@suse.de>
> Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
> ---
>  drivers/virtio/virtio_ring.c | 12 ++++++++----
>  include/linux/virtio.h       |  2 +-
>  2 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index c5310eaf8b46..55cfecf030a1 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -289,12 +289,16 @@ static bool vring_use_dma_api(const struct virtio_device *vdev)
>  	return false;
>  }
>  
> -size_t virtio_max_dma_size(const struct virtio_device *vdev)
> +u32 virtio_max_dma_size(const struct virtio_device *vdev)
>  {
> -	size_t max_segment_size = SIZE_MAX;
> +	u32 max_segment_size = U32_MAX;
>  
> -	if (vring_use_dma_api(vdev))
> -		max_segment_size = dma_max_mapping_size(vdev->dev.parent);
> +	if (vring_use_dma_api(vdev)) {
> +		size_t max_dma_size = dma_max_mapping_size(vdev->dev.parent);
> +
> +		if (max_dma_size < max_segment_size)
> +			max_segment_size = max_dma_size;
> +	}
>  
>  	return max_segment_size;
>  }

Took a while for me to get this, it's confusing.  I think the issue is
really in virtio blk, so I would just change max_size there to size_t
and be done with it.




> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index b93238db94e3..1a605f408329 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -147,7 +147,7 @@ int virtio_device_restore(struct virtio_device *dev);
>  #endif
>  void virtio_reset_device(struct virtio_device *dev);
>  
> -size_t virtio_max_dma_size(const struct virtio_device *vdev);
> +u32 virtio_max_dma_size(const struct virtio_device *vdev);
>  
>  #define virtio_device_for_each_vq(vdev, vq) \
>  	list_for_each_entry(vq, &vdev->vqs, list)
> -- 
> 2.20.1

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Re: Re: [PATCH] virtio_ring: use u32 for virtio_max_dma_size

[zhenwei pi via Virtualization]

On 7/4/23 14:21, Michael S. Tsirkin wrote:
> On Wed, May 10, 2023 at 10:54:37AM +0800, zhenwei pi wrote:
>> Both split ring and packed ring use 32bits to describe the length of
>> a descriptor: see struct vring_desc and struct vring_packed_desc.
>> This means the max segment size supported by virtio is U32_MAX.
>>
>> An example of virtio_max_dma_size in virtio_blk.c:
>>    u32 v, max_size;
>>
>>    max_size = virtio_max_dma_size(vdev);  -> implicit convert
>>    err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SIZE_MAX,
>>                               struct virtio_blk_config, size_max, &v);
>>    max_size = min(max_size, v);
>>
>> There is a risk during implicit convert here, once virtio_max_dma_size
>> returns 4G, max_size becomes 0.
>>
>> Fixes: e6d6dd6c875e ("virtio: Introduce virtio_max_dma_size()")
>> Cc: Joerg Roedel <jroedel@suse.de>
>> Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
>> ---
>>   drivers/virtio/virtio_ring.c | 12 ++++++++----
>>   include/linux/virtio.h       |  2 +-
>>   2 files changed, 9 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
>> index c5310eaf8b46..55cfecf030a1 100644
>> --- a/drivers/virtio/virtio_ring.c
>> +++ b/drivers/virtio/virtio_ring.c
>> @@ -289,12 +289,16 @@ static bool vring_use_dma_api(const struct virtio_device *vdev)
>>   	return false;
>>   }
>>   
>> -size_t virtio_max_dma_size(const struct virtio_device *vdev)
>> +u32 virtio_max_dma_size(const struct virtio_device *vdev)
>>   {
>> -	size_t max_segment_size = SIZE_MAX;
>> +	u32 max_segment_size = U32_MAX;
>>   
>> -	if (vring_use_dma_api(vdev))
>> -		max_segment_size = dma_max_mapping_size(vdev->dev.parent);
>> +	if (vring_use_dma_api(vdev)) {
>> +		size_t max_dma_size = dma_max_mapping_size(vdev->dev.parent);
>> +
>> +		if (max_dma_size < max_segment_size)
>> +			max_segment_size = max_dma_size;
>> +	}
>>   
>>   	return max_segment_size;
>>   }
> 
> Took a while for me to get this, it's confusing.  I think the issue is
> really in virtio blk, so I would just change max_size there to size_t
> and be done with it.
> 
> 

Fine.

> 
> 
>> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
>> index b93238db94e3..1a605f408329 100644
>> --- a/include/linux/virtio.h
>> +++ b/include/linux/virtio.h
>> @@ -147,7 +147,7 @@ int virtio_device_restore(struct virtio_device *dev);
>>   #endif
>>   void virtio_reset_device(struct virtio_device *dev);
>>   
>> -size_t virtio_max_dma_size(const struct virtio_device *vdev);
>> +u32 virtio_max_dma_size(const struct virtio_device *vdev);
>>   
>>   #define virtio_device_for_each_vq(vdev, vq) \
>>   	list_for_each_entry(vq, &vdev->vqs, list)
>> -- 
>> 2.20.1
> 

-- 
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