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 <[email protected]>
Signed-off-by: zhenwei pi <[email protected]>
---
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
On Wed, 10 May 2023 10:54:37 +0800, zhenwei pi <[email protected]> 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 <[email protected]>
> Signed-off-by: zhenwei pi <[email protected]>
> ---
> 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
>
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 <[email protected]>
> Signed-off-by: zhenwei pi <[email protected]>
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
On Wed, May 10, 2023 at 11:26:54AM +0800, Xuan Zhuo wrote:
> On Wed, 10 May 2023 10:54:37 +0800, zhenwei pi <[email protected]> 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 <[email protected]>
> > Signed-off-by: zhenwei pi <[email protected]>
> > ---
> > 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
> >
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 <[email protected]>
>> Signed-off-by: zhenwei pi <[email protected]>
>
>
> 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
>
--
zhenwei pi
On Wed, May 10, 2023 at 11:44 AM Michael S. Tsirkin <[email protected]> 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 <[email protected]> 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 <[email protected]>
> > > Signed-off-by: zhenwei pi <[email protected]>
> > > ---
> > > 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
> > >
>
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 <[email protected]> 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 <[email protected]> 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 <[email protected]>
> > > > Signed-off-by: zhenwei pi <[email protected]>
> > > > ---
> > > > 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
> > > >
> >
On 5/10/23 11:26, Xuan Zhuo wrote:
> On Wed, 10 May 2023 10:54:37 +0800, zhenwei pi <[email protected]> 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 <[email protected]>
>> Signed-off-by: zhenwei pi <[email protected]>
>> ---
>> 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
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 <[email protected]> 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 <[email protected]> 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 <[email protected]>
>>>>> Signed-off-by: zhenwei pi <[email protected]>
>>>>> ---
>>>>> 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
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 <[email protected]>
> Signed-off-by: zhenwei pi <[email protected]>
> ---
> 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
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 <[email protected]>
>> Signed-off-by: zhenwei pi <[email protected]>
>> ---
>> 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
>
--
zhenwei pi