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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS 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 42861C282CB for ; Tue, 5 Feb 2019 20:50:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1489C2083B for ; Tue, 5 Feb 2019 20:50:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729300AbfBEUuK (ORCPT ); Tue, 5 Feb 2019 15:50:10 -0500 Received: from mx1.redhat.com ([209.132.183.28]:49144 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727000AbfBEUuK (ORCPT ); Tue, 5 Feb 2019 15:50:10 -0500 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D8D423D95D; Tue, 5 Feb 2019 20:50:08 +0000 (UTC) Received: from redhat.com (ovpn-116-138.sin2.redhat.com [10.67.116.138]) by smtp.corp.redhat.com (Postfix) with SMTP id 0F0F31001F4D; Tue, 5 Feb 2019 20:49:43 +0000 (UTC) Date: Tue, 5 Feb 2019 15:49:41 -0500 From: "Michael S. Tsirkin" To: Nitesh Narayan Lal Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, lcapitulino@redhat.com, pagupta@redhat.com, wei.w.wang@intel.com, yang.zhang.wz@gmail.com, riel@surriel.com, david@redhat.com, dodgen@google.com, konrad.wilk@oracle.com, dhildenb@redhat.com, aarcange@redhat.com Subject: Re: [RFC][Patch v8 5/7] virtio: Enables to add a single descriptor to the host Message-ID: <20190205154545-mutt-send-email-mst@kernel.org> References: <20190204201854.2328-1-nitesh@redhat.com> <20190204201854.2328-6-nitesh@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190204201854.2328-6-nitesh@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Tue, 05 Feb 2019 20:50:09 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 04, 2019 at 03:18:52PM -0500, Nitesh Narayan Lal wrote: > This patch enables the caller to expose a single buffers to the > other end using vring descriptor. It also allows the caller to > perform this action in synchornous manner by using virtqueue_kick_sync. > > Signed-off-by: Nitesh Narayan Lal I am not sure why do we need this API. Polling in guest until host runs isn't great either since these might be running on the same host CPU. > --- > drivers/virtio/virtio_ring.c | 72 ++++++++++++++++++++++++++++++++++++ > include/linux/virtio.h | 4 ++ > 2 files changed, 76 insertions(+) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index cd7e755484e3..93c161ac6a28 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -1695,6 +1695,52 @@ static inline int virtqueue_add(struct virtqueue *_vq, > out_sgs, in_sgs, data, ctx, gfp); > } > > +/** > + * virtqueue_add_desc - add a buffer to a chain using a vring desc > + * @vq: the struct virtqueue we're talking about. > + * @addr: address of the buffer to add. > + * @len: length of the buffer. > + * @in: set if the buffer is for the device to write. > + * > + * Returns zero or a negative error (ie. ENOSPC, ENOMEM, EIO). > + */ > +int virtqueue_add_desc(struct virtqueue *_vq, u64 addr, u32 len, int in) > +{ > + struct vring_virtqueue *vq = to_vvq(_vq); > + struct vring_desc *desc = vq->split.vring.desc; > + u16 flags = in ? VRING_DESC_F_WRITE : 0; > + unsigned int i; > + void *data = (void *)addr; > + int avail_idx; > + > + /* Sanity check */ > + if (!_vq) > + return -EINVAL; > + > + START_USE(vq); > + if (unlikely(vq->broken)) { > + END_USE(vq); > + return -EIO; > + } > + > + i = vq->free_head; > + flags &= ~VRING_DESC_F_NEXT; > + desc[i].flags = cpu_to_virtio16(_vq->vdev, flags); > + desc[i].addr = cpu_to_virtio64(_vq->vdev, addr); > + desc[i].len = cpu_to_virtio32(_vq->vdev, len); > + > + vq->vq.num_free--; > + vq->free_head = virtio16_to_cpu(_vq->vdev, desc[i].next); > + vq->split.desc_state[i].data = data; > + vq->split.avail_idx_shadow = 1; > + avail_idx = vq->split.avail_idx_shadow; > + vq->split.vring.avail->idx = cpu_to_virtio16(_vq->vdev, avail_idx); > + vq->num_added = 1; > + END_USE(vq); > + return 0; > +} > +EXPORT_SYMBOL_GPL(virtqueue_add_desc); > + > /** > * virtqueue_add_sgs - expose buffers to other end > * @vq: the struct virtqueue we're talking about. > @@ -1842,6 +1888,32 @@ bool virtqueue_notify(struct virtqueue *_vq) > } > EXPORT_SYMBOL_GPL(virtqueue_notify); > > +/** > + * virtqueue_kick_sync - update after add_buf and busy wait till update is done > + * @vq: the struct virtqueue > + * > + * After one or more virtqueue_add_* calls, invoke this to kick > + * the other side. Busy wait till the other side is done with the update. > + * > + * Caller must ensure we don't call this with other virtqueue > + * operations at the same time (except where noted). > + * > + * Returns false if kick failed, otherwise true. > + */ > +bool virtqueue_kick_sync(struct virtqueue *vq) > +{ > + u32 len; > + > + if (likely(virtqueue_kick(vq))) { > + while (!virtqueue_get_buf(vq, &len) && > + !virtqueue_is_broken(vq)) > + cpu_relax(); > + return true; > + } > + return false; > +} > +EXPORT_SYMBOL_GPL(virtqueue_kick_sync); > + > /** > * virtqueue_kick - update after add_buf > * @vq: the struct virtqueue > diff --git a/include/linux/virtio.h b/include/linux/virtio.h > index fa1b5da2804e..58943a3a0e8d 100644 > --- a/include/linux/virtio.h > +++ b/include/linux/virtio.h > @@ -57,6 +57,10 @@ int virtqueue_add_sgs(struct virtqueue *vq, > unsigned int in_sgs, > void *data, > gfp_t gfp); > +/* A desc with this init id is treated as an invalid desc */ > +int virtqueue_add_desc(struct virtqueue *_vq, u64 addr, u32 len, int in); > + > +bool virtqueue_kick_sync(struct virtqueue *vq); > > bool virtqueue_kick(struct virtqueue *vq); > > -- > 2.17.2