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,URIBL_BLOCKED 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 7E384C282C2 for ; Wed, 23 Jan 2019 03:49:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 55BC921726 for ; Wed, 23 Jan 2019 03:49:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727201AbfAWDtj (ORCPT ); Tue, 22 Jan 2019 22:49:39 -0500 Received: from mx1.redhat.com ([209.132.183.28]:55778 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727101AbfAWDt3 (ORCPT ); Tue, 22 Jan 2019 22:49:29 -0500 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 675AC8764F; Wed, 23 Jan 2019 03:49:29 +0000 (UTC) Received: from redhat.com (ovpn-122-113.rdu2.redhat.com [10.10.122.113]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9D1B360C67; Wed, 23 Jan 2019 03:49:28 +0000 (UTC) Date: Tue, 22 Jan 2019 22:49:28 -0500 From: "Michael S. Tsirkin" To: Jason Wang Cc: Tiwei Bie , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, virtio-dev@lists.oasis-open.org Subject: Re: [virtio-dev] [PATCH] virtio: support VIRTIO_F_ORDER_PLATFORM Message-ID: <20190122224203-mutt-send-email-mst@kernel.org> References: <20190122170346.6279-1-tiwei.bie@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Wed, 23 Jan 2019 03:49:29 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 23, 2019 at 11:08:04AM +0800, Jason Wang wrote: > > On 2019/1/23 上午1:03, Tiwei Bie wrote: > > This patch introduces the support for VIRTIO_F_ORDER_PLATFORM. > > When this feature is negotiated, driver will use the barriers > > suitable for hardware devices. > > > > Signed-off-by: Tiwei Bie > > --- > > drivers/virtio/virtio_ring.c | 8 ++++++++ > > include/uapi/linux/virtio_config.h | 6 ++++++ > > 2 files changed, 14 insertions(+) > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > > index cd7e755484e3..27d3f057493e 100644 > > --- a/drivers/virtio/virtio_ring.c > > +++ b/drivers/virtio/virtio_ring.c > > @@ -1609,6 +1609,9 @@ static struct virtqueue *vring_create_virtqueue_packed( > > !context; > > vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX); > > + if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM)) > > + vq->weak_barriers = false; > > + > > vq->packed.ring_dma_addr = ring_dma_addr; > > vq->packed.driver_event_dma_addr = driver_event_dma_addr; > > vq->packed.device_event_dma_addr = device_event_dma_addr; > > @@ -2079,6 +2082,9 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index, > > !context; > > vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX); > > + if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM)) > > + vq->weak_barriers = false; > > + > > vq->split.queue_dma_addr = 0; > > vq->split.queue_size_in_bytes = 0; > > @@ -2213,6 +2219,8 @@ void vring_transport_features(struct virtio_device *vdev) > > break; > > case VIRTIO_F_RING_PACKED: > > break; > > + case VIRTIO_F_ORDER_PLATFORM: > > + break; > > default: > > /* We don't understand this bit. */ > > __virtio_clear_bit(vdev, i); > > diff --git a/include/uapi/linux/virtio_config.h b/include/uapi/linux/virtio_config.h > > index 1196e1c1d4f6..ff8e7dc9d4dd 100644 > > --- a/include/uapi/linux/virtio_config.h > > +++ b/include/uapi/linux/virtio_config.h > > @@ -78,6 +78,12 @@ > > /* This feature indicates support for the packed virtqueue layout. */ > > #define VIRTIO_F_RING_PACKED 34 > > +/* > > + * This feature indicates that memory accesses by the driver and the > > + * device are ordered in a way described by the platform. > > + */ > > +#define VIRTIO_F_ORDER_PLATFORM 36 > > + > > /* > > * Does the device support Single Root I/O Virtualization? > > */ > > > I wonder whether or not this is sufficient. Is dma barrier implies a mmio > barrier? Looks not. IIUC we don't need an mmio barrier because we are using a serializing API: Documentation/memory-barriers.txt says: Note that, when using writel(), a prior wmb() is not needed to guarantee that the cache coherent memory writes have completed before writing to the MMIO region. > See ia64/include/asm/barrier.h: > >  * Note: "mb()" and its variants cannot be used as a fence to order >  * accesses to memory mapped I/O registers.  For that, mf.a needs to >  * be used.  However, we don't want to always use mf.a because (a) >  * it's (presumably) much slower than mf and (b) mf.a is supported for >  * sequential memory pages only. >  */ > #define mb()            ia64_mf() > #define rmb()           mb() > #define wmb()           mb() > > #define dma_rmb()       mb() > =>efine dma_wmb()       mb() > > Thanks Frankly no idea about ia64. Sorry. Are any less esoteric platforms affected? -- MST