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Tsirkin" To: Jason Wang Cc: Xuan Zhuo , zhenwei pi , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Joerg Roedel Subject: Re: [PATCH] virtio_ring: use u32 for virtio_max_dma_size Message-ID: <20230510000603-mutt-send-email-mst@kernel.org> References: <20230510025437.377807-1-pizhenwei@bytedance.com> <1683689214.9647853-1-xuanzhuo@linux.alibaba.com> <20230509233907-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 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 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 > > > > Signed-off-by: zhenwei pi > > > > --- > > > > 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 > > > > > >