From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0F934C77B7D for ; Wed, 10 May 2023 03:30:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229565AbjEJDaD (ORCPT ); Tue, 9 May 2023 23:30:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37254 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235121AbjEJD37 (ORCPT ); Tue, 9 May 2023 23:29:59 -0400 Received: from out30-113.freemail.mail.aliyun.com (out30-113.freemail.mail.aliyun.com [115.124.30.113]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 38B0391 for ; Tue, 9 May 2023 20:29:56 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R131e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046050;MF=xuanzhuo@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0ViDxAvy_1683689393; Received: from localhost(mailfrom:xuanzhuo@linux.alibaba.com fp:SMTPD_---0ViDxAvy_1683689393) by smtp.aliyun-inc.com; Wed, 10 May 2023 11:29:54 +0800 Message-ID: <1683689214.9647853-1-xuanzhuo@linux.alibaba.com> Subject: Re: [PATCH] virtio_ring: use u32 for virtio_max_dma_size Date: Wed, 10 May 2023 11:26:54 +0800 From: Xuan Zhuo To: zhenwei pi Cc: virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, zhenwei pi , Joerg Roedel , mst@redhat.com, jasowang@redhat.com References: <20230510025437.377807-1-pizhenwei@bytedance.com> In-Reply-To: <20230510025437.377807-1-pizhenwei@bytedance.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > { > - 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 >