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Tue, 09 May 2023 20:39:25 -0700 (PDT) X-Google-Smtp-Source: ACHHUZ6sYk9M1+ioaOc46/jtM0pADUa1SIsRL3bgJIdk7tzU+GlllerCbudekFfug0+600+8xihsEw== X-Received: by 2002:a17:907:a429:b0:94a:8e19:6aba with SMTP id sg41-20020a170907a42900b0094a8e196abamr12998174ejc.21.1683689964809; Tue, 09 May 2023 20:39:24 -0700 (PDT) Received: from redhat.com ([176.119.195.36]) by smtp.gmail.com with ESMTPSA id bn13-20020a170906c0cd00b0096599bf7029sm2129152ejb.145.2023.05.09.20.39.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 May 2023 20:39:24 -0700 (PDT) Date: Tue, 9 May 2023 23:39:19 -0400 From: "Michael S. Tsirkin" To: Xuan Zhuo Subject: Re: [PATCH] virtio_ring: use u32 for virtio_max_dma_size Message-ID: <20230509233907-mutt-send-email-mst@kernel.org> References: <20230510025437.377807-1-pizhenwei@bytedance.com> <1683689214.9647853-1-xuanzhuo@linux.alibaba.com> MIME-Version: 1.0 In-Reply-To: <1683689214.9647853-1-xuanzhuo@linux.alibaba.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: Joerg Roedel , linux-kernel@vger.kernel.org, zhenwei pi , virtualization@lists.linux-foundation.org X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" 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. > > { > > - 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 > > _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization