From nobody Tue Dec 2 01:03:56 2025 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 8DEBC2D323D for ; Tue, 25 Nov 2025 07:09:54 +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=1764054596; cv=none; b=qCHgVd3xK/ylUXN4J9Vl/3fx3t7gCsbL6+BxOBiExx25nVlLwnU1CiEaARZiy8gf7tn9TxNIyVYc2e5RN+6Lmc0BSjZT/VN9JD1H8NhgLuaBVHwOqojfKxtKEAaJl/w416/wkc/BcxVOuvHBZYa+/vfgXcCtoRTfhir61OrzMBA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764054596; c=relaxed/simple; bh=Wx+2qzNeKc343CzDtkTZzpaBFSZw3rZNk6WKEivnL3Q=; h=From:To:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=p8wrkiSkSKVU9QKGZSugs00xrtjaQ4QBdnisBJZ38m4VhHrHHoIY42RvWJauYm7w6Ydu0Kv8MkMiw5JXuSUITaSLoVhHwFkWQEF05G/uxOwkteyHEZi8HENOGQHy7VlAigZl1Tg2ufwEjtGQdlImwrX5EyV3+3AAbJBKuQ7G9MM= 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=IC+1PnYL; 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="IC+1PnYL" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1764054593; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=K3VKBAegh1DAGoGVZ8mSzYBi+zKWMLuUYc+aq7Y2Vn4=; b=IC+1PnYLMIZ+eKeICIKk40J2DNN924ymTwpx7X/3/Ilo9kS4gXH23IkIw5NwZapvwuz/+g qc5r9y0Nxn7ARrpxrKZgFJ/2Th9/91twnhGWlvzyeoKnBZG8PJkXA6+UK6Io1pONTadoNF /Ww7xAHRQzMi/VGN6LoRAHkkg0rIUf8= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-617-7kQv1jI9PXeBSVcgIV4jdw-1; Tue, 25 Nov 2025 02:09:51 -0500 X-MC-Unique: 7kQv1jI9PXeBSVcgIV4jdw-1 X-Mimecast-MFC-AGG-ID: 7kQv1jI9PXeBSVcgIV4jdw_1764054590 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-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 7B822180035F; Tue, 25 Nov 2025 07:09:50 +0000 (UTC) Received: from localhost.localdomain (unknown [10.72.120.4]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 8A02C195608E; Tue, 25 Nov 2025 07:09:46 +0000 (UTC) From: Jason Wang To: mst@redhat.com, jasowang@redhat.com, xuanzhuo@linux.alibaba.com, eperezma@redhat.com, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org Subject: [PATCH V9 14/19] virtio_ring: determine descriptor flags at one time Date: Tue, 25 Nov 2025 15:08:33 +0800 Message-ID: <20251125070838.70736-15-jasowang@redhat.com> In-Reply-To: <20251125070838.70736-1-jasowang@redhat.com> References: <20251125070838.70736-1-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 4e905dc7b6cb..dbcd6f26df7d 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -575,7 +575,7 @@ 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 @@ -635,42 +635,40 @@ 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