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Xuan Zhuo

2023-May-10 03:26 UTC

[PATCH] virtio_ring: use u32 for virtio_max_dma_size

On Wed, 10 May 2023 10:54:37 +0800, zhenwei pi <pizhenwei at
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 at suse.de>
> Signed-off-by: zhenwei pi <pizhenwei at 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
>

Michael S. Tsirkin

2023-May-10 03:39 UTC

head link

[PATCH] virtio_ring: use u32 for virtio_max_dma_size

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 at
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 at suse.de>
> > Signed-off-by: zhenwei pi <pizhenwei at 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
> >

zhenwei pi

2023-May-10 07:52 UTC

head link

[PATCH] virtio_ring: use u32 for virtio_max_dma_size

On 5/10/23 11:26, Xuan Zhuo wrote:> On Wed, 10 May 2023 10:54:37 +0800, zhenwei pi <pizhenwei at
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 at suse.de>
>> Signed-off-by: zhenwei pi <pizhenwei at 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
>>
-- 
zhenwei pi

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