From nobody Wed Feb 11 00:54:56 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 E4DE61CA81 for ; Tue, 23 Apr 2024 03:24:25 +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=1713842667; cv=none; b=W+LVDytD9nLgkIfUghVEZFb9Zy2TRlQqNbJ8H94Iaa+w0kaTjPpD7bWB8ortUKrCXZEoaYPq/F2A5iSA+c5K7jlWf/c5eg4+vCQZbJXVIAUWn1N9eulBchZ86u1pS7k32BMSAfrGHmuFq7RBB+d5c6eZyajdI4oiXQhBh445JP4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713842667; c=relaxed/simple; bh=LRQl9lv2M8QSOZPByVQiOvj73HlXJF/ZAmTJj/fGtZM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=LGi37c1wUxRWyXxUDfNw7kQUwQl4tL6OLSLurP7fH47e/TSJ6+QGTzrA83epfpzdchqTF4Gn5i8Vn3A3RMGkwTA3Qgg/m1PFeJFqX98NX7ckJnINM6zyw0ixe23j9H8orT6JhEXJn+jsvWVKR18eVHTzG+3jyPkH+9rrkQzWpBE= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none 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=XNPRos7K; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none 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="XNPRos7K" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1713842664; 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=/BuCY3v8aKDYplSDVVzxpIvd+2taH57MWRDqJV/LGJ4=; b=XNPRos7K5V8ohkM4l1Md0+oWydcxM/C0+uZqAUOPZnUyn4sQEUpsxCWj+ry/G5xYSocm4u QW3rfBiKVAHies/orIlisLdnF51dIkzOHwRvFR7sai0Fw3PN0mHS8qxvsgIwYpCb8N12/E ngzT7J8p3RilDkt0D1g67dqi4i/sdEY= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-127-O2h3yeDePoGQV3yoIrddFw-1; Mon, 22 Apr 2024 23:24:21 -0400 X-MC-Unique: O2h3yeDePoGQV3yoIrddFw-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (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 mimecast-mx02.redhat.com (Postfix) with ESMTPS id 0E0F380591B; Tue, 23 Apr 2024 03:24:21 +0000 (UTC) Received: from gshan-thinkpadx1nanogen2.remote.csb (unknown [10.64.136.57]) by smtp.corp.redhat.com (Postfix) with ESMTPS id DD1E51BDAA; Tue, 23 Apr 2024 03:24:18 +0000 (UTC) From: Gavin Shan To: virtualization@lists.linux.dev Cc: linux-kernel@vger.kernel.org, mst@redhat.com, jasowang@redhat.com, shan.gavin@gmail.com Subject: [PATCH 2/4] vhost: Improve vhost_get_avail_idx() with smp_rmb() Date: Tue, 23 Apr 2024 13:24:05 +1000 Message-ID: <20240423032407.262329-3-gshan@redhat.com> In-Reply-To: <20240423032407.262329-1-gshan@redhat.com> References: <20240423032407.262329-1-gshan@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.5 Content-Type: text/plain; charset="utf-8" All the callers of vhost_get_avail_idx() are concerned to the memory barrier, imposed by smp_rmb() to ensure the order of the available ring entry read and avail_idx read. Improve vhost_get_avail_idx() so that smp_rmb() is executed when the avail_idx is advanced. With it, the callers needn't to worry about the memory barrier. No functional change intended. Suggested-by: Michael S. Tsirkin Signed-off-by: Gavin Shan --- drivers/vhost/vhost.c | 91 ++++++++++++++++--------------------------- 1 file changed, 34 insertions(+), 57 deletions(-) diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index ef7942103232..b3adc0bc9e72 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -1290,10 +1290,34 @@ static void vhost_dev_unlock_vqs(struct vhost_dev *= d) mutex_unlock(&d->vqs[i]->mutex); } =20 -static inline int vhost_get_avail_idx(struct vhost_virtqueue *vq, - __virtio16 *idx) +static inline int vhost_get_avail_idx(struct vhost_virtqueue *vq) { - return vhost_get_avail(vq, *idx, &vq->avail->idx); + __virtio16 avail_idx; + int r; + + r =3D vhost_get_avail(vq, avail_idx, &vq->avail->idx); + if (unlikely(r)) { + vq_err(vq, "Failed to access avail idx at %p\n", + &vq->avail->idx); + return r; + } + + vq->avail_idx =3D vhost16_to_cpu(vq, avail_idx); + if (vq->avail_idx !=3D vq->last_avail_idx) { + /* Ensure the available ring entry read happens + * before the avail_idx read when the avail_idx + * is advanced. + */ + smp_rmb(); + } + + if (unlikely((u16)(vq->avail_idx - vq->last_avail_idx) > vq->num)) { + vq_err(vq, "Invalid avail index change from %u to %u", + vq->last_avail_idx, vq->avail_idx); + return -EINVAL; + } + + return 0; } =20 static inline int vhost_get_avail_head(struct vhost_virtqueue *vq, @@ -2498,35 +2522,19 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq, { struct vring_desc desc; unsigned int i, head, found =3D 0; - __virtio16 avail_idx; __virtio16 ring_head; int ret, access; =20 - /* Check it isn't doing very strange things with descriptor numbers. */ if (vq->avail_idx =3D=3D vq->last_avail_idx) { - if (unlikely(vhost_get_avail_idx(vq, &avail_idx))) { - vq_err(vq, "Failed to access avail idx at %p\n", - &vq->avail->idx); - return -EFAULT; - } - vq->avail_idx =3D vhost16_to_cpu(vq, avail_idx); - - if (unlikely((u16)(vq->avail_idx - vq->last_avail_idx) > vq->num)) { - vq_err(vq, "Guest moved avail index from %u to %u", - vq->last_avail_idx, vq->avail_idx); - return -EFAULT; - } + ret =3D vhost_get_avail_idx(vq); + if (unlikely(ret)) + return ret; =20 /* If there's nothing new since last we looked, return * invalid. */ if (vq->avail_idx =3D=3D vq->last_avail_idx) return vq->num; - - /* Only get avail ring entries after they have been - * exposed by guest. - */ - smp_rmb(); } =20 /* Grab the next descriptor number they're advertising, and increment @@ -2787,35 +2795,19 @@ EXPORT_SYMBOL_GPL(vhost_add_used_and_signal_n); /* return true if we're sure that avaiable ring is empty */ bool vhost_vq_avail_empty(struct vhost_dev *dev, struct vhost_virtqueue *v= q) { - __virtio16 avail_idx; - int r; - if (vq->avail_idx !=3D vq->last_avail_idx) return false; =20 - r =3D vhost_get_avail_idx(vq, &avail_idx); - if (unlikely(r)) - return false; - - vq->avail_idx =3D vhost16_to_cpu(vq, avail_idx); - if (vq->avail_idx !=3D vq->last_avail_idx) { - /* Since we have updated avail_idx, the following - * call to vhost_get_vq_desc() will read available - * ring entries. Make sure that read happens after - * the avail_idx read. - */ - smp_rmb(); + if (unlikely(vhost_get_avail_idx(vq))) return false; - } =20 - return true; + return vq->avail_idx =3D=3D vq->last_avail_idx; } EXPORT_SYMBOL_GPL(vhost_vq_avail_empty); =20 /* OK, now we need to know about added descriptors. */ bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq) { - __virtio16 avail_idx; int r; =20 if (!(vq->used_flags & VRING_USED_F_NO_NOTIFY)) @@ -2839,25 +2831,10 @@ bool vhost_enable_notify(struct vhost_dev *dev, str= uct vhost_virtqueue *vq) /* They could have slipped one in as we were doing that: make * sure it's written, then check again. */ smp_mb(); - r =3D vhost_get_avail_idx(vq, &avail_idx); - if (r) { - vq_err(vq, "Failed to check avail idx at %p: %d\n", - &vq->avail->idx, r); + if (unlikely(vhost_get_avail_idx(vq))) return false; - } - - vq->avail_idx =3D vhost16_to_cpu(vq, avail_idx); - if (vq->avail_idx !=3D vq->last_avail_idx) { - /* Since we have updated avail_idx, the following - * call to vhost_get_vq_desc() will read available - * ring entries. Make sure that read happens after - * the avail_idx read. - */ - smp_rmb(); - return true; - } =20 - return false; + return vq->avail_idx !=3D vq->last_avail_idx; } EXPORT_SYMBOL_GPL(vhost_enable_notify); =20 --=20 2.44.0