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 X-Spam-Level: X-Spam-Status: No, score=-16.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 17D57C433B4 for ; Mon, 17 May 2021 09:09:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F0E9A6100B for ; Mon, 17 May 2021 09:09:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235852AbhEQJKr (ORCPT ); Mon, 17 May 2021 05:10:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52546 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235760AbhEQJKb (ORCPT ); Mon, 17 May 2021 05:10:31 -0400 Received: from mail-pg1-x531.google.com (mail-pg1-x531.google.com [IPv6:2607:f8b0:4864:20::531]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DBA13C06174A for ; Mon, 17 May 2021 02:09:05 -0700 (PDT) Received: by mail-pg1-x531.google.com with SMTP id i5so4246603pgm.0 for ; Mon, 17 May 2021 02:09:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=jhBni8X9QlkQeBD83OCCLKYlOWpAQU218tM5q8w0H+0=; b=zNeom1/c4JETV9Ylyw5hZIeynCnit4Wbt6c304XuokR0k+a45tZD2uBp9M/n2N3uPR oBjm53E1ySAaL558bAQ0BYVu8DPdQ6/nQ7w4DXMAcfFp9p5Ld7Guwong4ue91XQ58blM kSGxZHC0uD47KdXx2/3x3lhH0JcmilfY3sUJHo+J2sU4er1D6p8ecHzsbg8q1Dy6Ddee V3h9sLwoJ6GD4m7Zy5gO0hlWJ2RHlw40PRd70IMgro2mIKetn8C5wIKkonZFb6ftHrsr vdCMgkggSk6rwBMJzGkRKlvl3lpQRoOH3vl2usBrSHwQ/zeh1sev0K28fVvm7BfVq/YE jHLA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=jhBni8X9QlkQeBD83OCCLKYlOWpAQU218tM5q8w0H+0=; b=ajfjKVVwgezj+97zRRCjTJAtgfuldYLrU1V3BrnppXtt2QJV1KisgHUXOA+b6+DBre ojT3SjLfjmJRIH+rzFEyO0ZNo2J5PWApU7Nq0nUj5qcVQ2XfFzpWwJy+Wh6y1qp9AbZe EJEhxQmWOzF63JCdzPt2NsuJx8eTDoTMf1iy0QRw1npTW0/kjrxg8s5gmssM+Lg27U55 i+AS6qkPGqibejUojfGWs95Y7HavgLydRCJr2DD4BlsaDTAILuAfrD4SInC4LJJaly+v Tu9WAjOOrN27nXJgBKRTZLehLl75KA0f0AzpICGaCEBLwXueo50FitDllCa0ijJbxyWX gcCQ== X-Gm-Message-State: AOAM533+3UZupwe1bqtgvZz56kpktXpHOMRcxQU2f3DKg2zFhVPDkPyj HgucVwBcKgYoGjwitGqlRlGe X-Google-Smtp-Source: ABdhPJy/hEKqaQGNe2OZcLBRD+qHcI1uhJO0z8QLc8+PhEyP7nCQSnHbBxvbObTjLSCaov+8hQeeVA== X-Received: by 2002:aa7:95b6:0:b029:28e:aa31:dd3c with SMTP id a22-20020aa795b60000b029028eaa31dd3cmr59113227pfk.43.1621242545386; Mon, 17 May 2021 02:09:05 -0700 (PDT) Received: from localhost ([139.177.225.253]) by smtp.gmail.com with ESMTPSA id t7sm2956257pjr.29.2021.05.17.02.09.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 May 2021 02:09:05 -0700 (PDT) From: Xie Yongji To: mst@redhat.com, jasowang@redhat.com, stefanha@redhat.com Cc: amit@kernel.org, arei.gonglei@huawei.com, airlied@linux.ie, kraxel@redhat.com, dan.j.williams@intel.com, johannes@sipsolutions.net, ohad@wizery.com, bjorn.andersson@linaro.org, david@redhat.com, vgoyal@redhat.com, miklos@szeredi.hu, sgarzare@redhat.com, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: [RFC PATCH 01/17] virtio_ring: Avoid reading unneeded used length Date: Mon, 17 May 2021 17:08:20 +0800 Message-Id: <20210517090836.533-2-xieyongji@bytedance.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210517090836.533-1-xieyongji@bytedance.com> References: <20210517090836.533-1-xieyongji@bytedance.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If device driver doesn't need used length, it can pass a NULL len in virtqueue_get_buf()/virtqueue_get_buf_ctx(). Then we can avoid reading and validating the len value in used ring entries. Signed-off-by: Xie Yongji --- drivers/virtio/virtio_ring.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 54e12dd91310..d999a1d6d271 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -772,7 +772,8 @@ static void *virtqueue_get_buf_ctx_split(struct virtqueue *_vq, last_used = (vq->last_used_idx & (vq->split.vring.num - 1)); i = virtio32_to_cpu(_vq->vdev, vq->split.vring.used->ring[last_used].id); - *len = virtio32_to_cpu(_vq->vdev, + if (len) + *len = virtio32_to_cpu(_vq->vdev, vq->split.vring.used->ring[last_used].len); if (unlikely(i >= vq->split.vring.num)) { @@ -1444,7 +1445,8 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, last_used = vq->last_used_idx; id = le16_to_cpu(vq->packed.vring.desc[last_used].id); - *len = le32_to_cpu(vq->packed.vring.desc[last_used].len); + if (len) + *len = le32_to_cpu(vq->packed.vring.desc[last_used].len); if (unlikely(id >= vq->packed.vring.num)) { BAD_RING(vq, "id %u out of range\n", id); -- 2.11.0