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 6E330C433EF for ; Wed, 23 Feb 2022 03:19:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237058AbiBWDTq (ORCPT ); Tue, 22 Feb 2022 22:19:46 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38110 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231871AbiBWDTp (ORCPT ); Tue, 22 Feb 2022 22:19:45 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 1110E33E86 for ; Tue, 22 Feb 2022 19:19:18 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1645586358; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=o10+oL16B6fHkAqAM1KRvbz+KhlX2puJg4tawglVFis=; b=X+X0TE6YVdT0Ka5v9UGhuT+L/KqzK2qaug3ic9THrguALHvD60jmpAQduemcWQ0LAmSD76 P77zVPb66iVBL3Bx8vbHksW2Vt/PYmMQQuyrE/mgqCsoFVu0kotrs9E+aqI36Rk27Rkt50 w4zwVlBWGeIzk7uEkKFyI5S0y7zd23U= Received: from mail-lf1-f69.google.com (mail-lf1-f69.google.com [209.85.167.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-623-zTaXhI0gNVCAwGqvANVyZg-1; Tue, 22 Feb 2022 22:19:16 -0500 X-MC-Unique: zTaXhI0gNVCAwGqvANVyZg-1 Received: by mail-lf1-f69.google.com with SMTP id j11-20020a19f50b000000b00443304eab91so3043142lfb.13 for ; Tue, 22 Feb 2022 19:19:16 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to; bh=o10+oL16B6fHkAqAM1KRvbz+KhlX2puJg4tawglVFis=; b=b7seu0rNncMhAXKBweo3CxpftuUMkIrIQAVgoI48bxmvVhz+LXDxG2CU4NqXRa4wrP mxjU7scE10ZtOLipEYnsR0i4Y16Xgcz0NOpShdM3Vir5HWTRb9/e3sAiaxa1NbSHaCdL mLCgCIt5Hd8YM/1pS0zcVRKfhRImKSyfz3VCMVM48zxyr59/wxy203Q4wUWumD6tznLv 6qciGw0Rc0W4OKoxoUeIYt8zKNFzukLvXInIwMjub1ajMuUV4Xi63KjNuItcB5g22pXK L3ajJ96arqf1DT4OGI+vB6c9unhHRK0tbypj3kzjzDixCPW/3NtS8UdTTjmpE3NwPCME Lssw== X-Gm-Message-State: AOAM533t+9QmkBz7vxQdG3HCHlreJnm2A/munqKrgzo/ByffsMXYiuI5 dHKvi+ABqRJ8Ysn4DZq4ouls3tvFZYgzPeFpwQwsILqijRoChjz36IrgnRBnJjoKisPqM+OzKWv uAl/mqdPYMqoJl1+x/MnTSKNlWBAS+n7q7wnzHwmq X-Received: by 2002:a05:6512:3147:b0:443:323d:179d with SMTP id s7-20020a056512314700b00443323d179dmr19712249lfi.98.1645586354933; Tue, 22 Feb 2022 19:19:14 -0800 (PST) X-Google-Smtp-Source: ABdhPJzC+VckbRDPD22Vw3cVRNOnTu5Dv3fTch6szAQ3aD8AdD7ESb4+dCSn4ACFp0ue/sa1Fe1eo+0wiUKb44UQGJA= X-Received: by 2002:a05:6512:3147:b0:443:323d:179d with SMTP id s7-20020a056512314700b00443323d179dmr19712239lfi.98.1645586354760; Tue, 22 Feb 2022 19:19:14 -0800 (PST) MIME-Version: 1.0 References: <20211108081324.14204-1-jasowang@redhat.com> In-Reply-To: <20211108081324.14204-1-jasowang@redhat.com> From: Jason Wang Date: Wed, 23 Feb 2022 11:19:03 +0800 Message-ID: Subject: Re: [PATCH] virtio_ring: aovid reading flag from the descriptor ring To: mst , jasowang , virtualization , linux-kernel Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 8, 2021 at 4:13 PM Jason Wang wrote: > > Commit 72b5e8958738 ("virtio-ring: store DMA metadata in desc_extra > for split virtqueue") tries to make it possible for the driver to not > read from the descriptor ring to prevent the device from corrupting > the descriptor ring. But it still read the descriptor flag from the > descriptor ring during buffer detach. > > This patch fixes by always store the descriptor flag no matter whether > DMA API is used and then we can avoid reading descriptor flag from the > descriptor ring. This eliminates the possibly of unexpected next > descriptor caused by the wrong flag (e.g the next flag). > > Signed-off-by: Jason Wang Michael, any comment for this? Thanks > --- > drivers/virtio/virtio_ring.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index 00f64f2f8b72..28734f4e57d3 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -583,7 +583,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq, > } > /* Last one doesn't continue. */ > desc[prev].flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT); > - if (!indirect && vq->use_dma_api) > + if (!indirect) > vq->split.desc_extra[prev & (vq->split.vring.num - 1)].flags &= > ~VRING_DESC_F_NEXT; > > @@ -713,7 +713,7 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head, > /* Put back on free list: unmap first-level descriptors and find end */ > i = head; > > - while (vq->split.vring.desc[i].flags & nextflag) { > + while (vq->split.desc_extra[i].flags & nextflag) { > vring_unmap_one_split(vq, i); > i = vq->split.desc_extra[i].next; > vq->vq.num_free++; > -- > 2.25.1 >