From nobody Tue Feb 10 04:12:36 2026 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5C6C82FD7D5 for ; Tue, 30 Dec 2025 06:47:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767077277; cv=none; b=kzz5ETRzILlSvnMy1HyDqQW3idSVqfT0XjMz0T4tEdza3qPFnVG9Prxoz6gumjqkEwIdE0VjX9tTPj+9BvyueXyewE5vpXtBVvgPSxHVhIBYEHQe76cZRyAdQgHfPywVvNcMDC40/XrB7tQ0s5I51D4Oe01ujTD2U+dH0PIEAuY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767077277; c=relaxed/simple; bh=2T+VmzY02RNZh4eu2RiFMdlY9HfozvNxjeOJCjeIvvM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=Pu109p2WNEEL09ycm26GcwK/7NROfJQd9v42kROwXrIz1dYntbuioVcPaS5eO/by3EC5hRyDLOqycay8A4mNn+kzzhMkic5BAgub5lWR3R9hLs+0VTA6kj6cZ7U6jyxyyrA0YZPjslLrvIEHWmMhvfaO2v1wRYw/bEGdL0BEeX4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=cE85zMVT; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="cE85zMVT" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1767077274; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ig2g+mSdEvnUp9CmjNCKFtRPPldZC0LNYdzsiKrQidI=; b=cE85zMVTzZNk8gQg3hTm2t0W7GFrBigtGOZhkMpJ+gjKvNacsdJrSruCn+9jxnihMEueH/ XkHm9uG3ZhroD67RomiXmGAzv5Z769tddQTEgLd1+htDZCLSfZPHLikfD7IoLv0jVMhY1F WVbtkt1pW7aIkcCzKdFRbClxO7kcsh0= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-137-eWW04LoOPdWLu4o0u-BJIw-1; Tue, 30 Dec 2025 01:47:50 -0500 X-MC-Unique: eWW04LoOPdWLu4o0u-BJIw-1 X-Mimecast-MFC-AGG-ID: eWW04LoOPdWLu4o0u-BJIw_1767077269 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 6229A195DE48; Tue, 30 Dec 2025 06:47:49 +0000 (UTC) Received: from localhost.localdomain (unknown [10.72.112.134]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 6867619560AB; Tue, 30 Dec 2025 06:47:46 +0000 (UTC) From: Jason Wang To: mst@redhat.com, jasowang@redhat.com Cc: xuanzhuo@linux.alibaba.com, eperezma@redhat.com, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org Subject: [PATCH V11 14/19] virtio_ring: determine descriptor flags at one time Date: Tue, 30 Dec 2025 14:46:44 +0800 Message-ID: <20251230064649.55597-15-jasowang@redhat.com> In-Reply-To: <20251230064649.55597-1-jasowang@redhat.com> References: <20251230064649.55597-1-jasowang@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Let's determine the last descriptor by counting the number of sg. This would be consistent with packed virtqueue implementation and ease the future in-order implementation. Acked-by: Eugenio P=C3=A9rez Reviewed-by: Xuan Zhuo Signed-off-by: Jason Wang --- drivers/virtio/virtio_ring.c | 28 +++++++++++++--------------- 1 file changed, 13 insertions(+), 15 deletions(-) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 29174a77eacd..33fa7fcdbd8a 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -574,7 +574,7 @@ static inline int virtqueue_add_split(struct vring_virt= queue *vq, struct vring_desc_extra *extra; struct scatterlist *sg; struct vring_desc *desc; - unsigned int i, n, avail, descs_used, prev, err_idx; + unsigned int i, n, avail, descs_used, err_idx, sg_count =3D 0; int head; bool indirect; =20 @@ -634,42 +634,40 @@ static inline int virtqueue_add_split(struct vring_vi= rtqueue *vq, for (sg =3D sgs[n]; sg; sg =3D sg_next(sg)) { dma_addr_t addr; u32 len; + u16 flags =3D 0; + + if (++sg_count !=3D total_sg) + flags |=3D VRING_DESC_F_NEXT; =20 if (vring_map_one_sg(vq, sg, DMA_TO_DEVICE, &addr, &len, premapped)) goto unmap_release; =20 - prev =3D i; /* Note that we trust indirect descriptor * table since it use stream DMA mapping. */ - i =3D virtqueue_add_desc_split(vq, desc, extra, i, addr, len, - VRING_DESC_F_NEXT, - premapped); + i =3D virtqueue_add_desc_split(vq, desc, extra, i, addr, + len, flags, premapped); } } for (; n < (out_sgs + in_sgs); n++) { for (sg =3D sgs[n]; sg; sg =3D sg_next(sg)) { dma_addr_t addr; u32 len; + u16 flags =3D VRING_DESC_F_WRITE; + + if (++sg_count !=3D total_sg) + flags |=3D VRING_DESC_F_NEXT; =20 if (vring_map_one_sg(vq, sg, DMA_FROM_DEVICE, &addr, &len, premapped)) goto unmap_release; =20 - prev =3D i; /* Note that we trust indirect descriptor * table since it use stream DMA mapping. */ - i =3D virtqueue_add_desc_split(vq, desc, extra, i, addr, len, - VRING_DESC_F_NEXT | - VRING_DESC_F_WRITE, - premapped); + i =3D virtqueue_add_desc_split(vq, desc, extra, i, addr, + len, flags, premapped); } } - /* Last one doesn't continue. */ - desc[prev].flags &=3D cpu_to_virtio16(vq->vq.vdev, ~VRING_DESC_F_NEXT); - if (!indirect && vring_need_unmap_buffer(vq, &extra[prev])) - vq->split.desc_extra[prev & (vq->split.vring.num - 1)].flags &=3D - ~VRING_DESC_F_NEXT; =20 if (indirect) { /* Now that the indirect table is filled in, map it. */ --=20 2.31.1