From nobody Mon Feb 9 06:25:18 2026 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 82AD31BC49 for ; Thu, 28 Mar 2024 00:22:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711585347; cv=none; b=EeXVbjuNBcFA4ASBiFIf7mxD4d6h19bVHSNMc+UzTQGgfs0NrFkU2zIFOML1UTzBqnh7pPc7OduVXNEPbYPOHvHI7u/yYJwQH2JLeeU7sco8hUrpRrEh9IVeF0tOojSq8+mVkkJgVJ5ku8jnOuKxFo53YsX+hi5mXAgpXY+X3JI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711585347; c=relaxed/simple; bh=NEWB7Jyx6ZTqoQYpQmN8i2qbWCNLe6BWjFi5j4OmaIg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=J99R0m7qrWLxHXcD/dap0XqaBh+K6fDmX4LzV6YqCNy4uH5OXhJvK2xFlqO4W6F2Ix4ViZzCANTRrlbuheCJs9Wpra1Pt1wMMvss4L8m8glWu7nnAQB5Svys3UAONKcQn2lYMFAGU3ebdPhdtIl70UVXEkteK60naYKc4gfaQFQ= 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=IR59b+Wo; arc=none smtp.client-ip=170.10.133.124 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="IR59b+Wo" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1711585344; 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=4ak0Cq/D1N2M9Qn2X1+lt/FpcfjVoz3V3sPZ0fz5NBc=; b=IR59b+WozRgzp90VLsFGZzIBvACvL8X4ihIead5eUtVLH7vFHp9W0brA3RoWa93JunNUjL O8zYgfS+yf/lUyHt7Fw/HXN4julc9/bNCcDxpTj4GpW7b333dfAW1ILqtIEwV1givsQHEW dLT7Z+ZeSHJyk/UZJyqXE6it0RepPIw= 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-526-Wz9J29WXMTaRPc9LhpVekA-1; Wed, 27 Mar 2024 20:22:21 -0400 X-MC-Unique: Wz9J29WXMTaRPc9LhpVekA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (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 B388B800265; Thu, 28 Mar 2024 00:22:19 +0000 (UTC) Received: from gshan-thinkpadx1nanogen2.remote.csb (unknown [10.64.136.81]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BBCDE2166B31; Thu, 28 Mar 2024 00:22:15 +0000 (UTC) From: Gavin Shan To: virtualization@lists.linux.dev Cc: linux-kernel@vger.kernel.org, mst@redhat.com, jasowang@redhat.com, will@kernel.org, davem@davemloft.net, stefanha@redhat.com, sgarzare@redhat.com, keirf@google.com, yihyu@redhat.com, shan.gavin@gmail.com Subject: [PATCH v3 3/3] vhost: Improve vhost_get_avail_idx() with smp_rmb() Date: Thu, 28 Mar 2024 10:21:49 +1000 Message-ID: <20240328002149.1141302-4-gshan@redhat.com> In-Reply-To: <20240328002149.1141302-1-gshan@redhat.com> References: <20240328002149.1141302-1-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 10.11.54.6 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. Suggested-by: Michael S. Tsirkin Signed-off-by: Gavin Shan Acked-by: Jason Wang --- drivers/vhost/vhost.c | 75 +++++++++++++++---------------------------- 1 file changed, 26 insertions(+), 49 deletions(-) diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 32686c79c41d..e6882f4f6ce2 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -1290,10 +1290,28 @@ 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(); + } + + return 0; } =20 static inline int vhost_get_avail_head(struct vhost_virtqueue *vq, @@ -2499,7 +2517,6 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq, struct vring_desc desc; unsigned int i, head, found =3D 0; u16 last_avail_idx; - __virtio16 avail_idx; __virtio16 ring_head; int ret, access; =20 @@ -2507,12 +2524,8 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq, last_avail_idx =3D vq->last_avail_idx; =20 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); + if (unlikely(vhost_get_avail_idx(vq))) return -EFAULT; - } - vq->avail_idx =3D vhost16_to_cpu(vq, avail_idx); =20 if (unlikely((u16)(vq->avail_idx - last_avail_idx) > vq->num)) { vq_err(vq, "Guest moved used index from %u to %u", @@ -2525,11 +2538,6 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq, */ if (vq->avail_idx =3D=3D 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 @@ -2790,35 +2798,19 @@ 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)) @@ -2842,25 +2834,10 @@ 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