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Date:   Tue, 4 Jul 2023 08:18:17 +0800
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Subject: PING Re: [PATCH] virtio_ring: use u32 for virtio_max_dma_size
To:     "Michael S. Tsirkin" <mst@redhat.com>
Cc:     Xuan Zhuo <xuanzhuo@linux.alibaba.com>,
        Jason Wang <jasowang@redhat.com>,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, Joerg Roedel <jroedel@suse.de>
References: <20230510025437.377807-1-pizhenwei@bytedance.com>
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From:   zhenwei pi <pizhenwei@bytedance.com>
In-Reply-To: <20230510000603-mutt-send-email-mst@kernel.org>
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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