Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755450AbbDNOUl (ORCPT ); Tue, 14 Apr 2015 10:20:41 -0400 Received: from e06smtp16.uk.ibm.com ([195.75.94.112]:36930 "EHLO e06smtp16.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753579AbbDNOUc (ORCPT ); Tue, 14 Apr 2015 10:20:32 -0400 Date: Tue, 14 Apr 2015 16:20:23 +0200 From: Cornelia Huck To: Greg Kurz Cc: Rusty Russell , "Michael S. Tsirkin" , linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCH v4 7/8] vhost: feature to set the vring endianness Message-ID: <20150414162023.2f8694fe.cornelia.huck@de.ibm.com> In-Reply-To: <20150410101627.31843.21710.stgit@bahia.local> References: <20150410101500.31843.61248.stgit@bahia.local> <20150410101627.31843.21710.stgit@bahia.local> Organization: IBM Deutschland Research & Development GmbH Vorsitzende des Aufsichtsrats: Martina Koederitz =?UTF-8?B?R2VzY2jDpGZ0c2bDvGhydW5nOg==?= Dirk Wittkopp Sitz der Gesellschaft: =?UTF-8?B?QsO2Ymxpbmdlbg==?= Registergericht: Amtsgericht Stuttgart, HRB 243294 X-Mailer: Claws Mail 3.8.0 (GTK+ 2.24.10; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15041414-0025-0000-0000-000004B85492 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2815 Lines: 91 On Fri, 10 Apr 2015 12:19:16 +0200 Greg Kurz wrote: > This patch brings cross-endian support to vhost when used to implement > legacy virtio devices. Since it is a relatively rare situation, the > feature availability is controlled by a kernel config option (not set > by default). > > The vq->is_le boolean field is added to cache the endianness to be > used for ring accesses. It defaults to native endian, as expected > by legacy virtio devices. When the ring gets active, we force little > endian if the device is modern. When the ring is deactivated, we > revert to the native endian default. > > If cross-endian was compiled in, a vq->user_be boolean field is added > so that userspace may request a specific endianness. This field is > used to override the default when activating the ring of a legacy > device. It has no effect on modern devices. > > Signed-off-by: Greg Kurz > --- > drivers/vhost/Kconfig | 10 ++++++ > drivers/vhost/vhost.c | 76 +++++++++++++++++++++++++++++++++++++++++++- > drivers/vhost/vhost.h | 12 +++++-- > include/uapi/linux/vhost.h | 9 +++++ > 4 files changed, 103 insertions(+), 4 deletions(-) > +#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY > +static long vhost_set_vring_big_endian(struct vhost_virtqueue *vq, > + int __user *argp) > +{ > + struct vhost_vring_state s; > + > + if (vq->private_data) > + return -EBUSY; > + > + if (copy_from_user(&s, argp, sizeof(s))) > + return -EFAULT; > + > + if (s.num && s.num != 1) Checking for s.num > 1 might be more obvious at a glance? > + return -EINVAL; > + > + vq->user_be = s.num; > + > + return 0; > +} > + (...) > +#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY > +static void vhost_init_is_le(struct vhost_virtqueue *vq) > +{ > + vq->is_le = vhost_has_feature(vq, VIRTIO_F_VERSION_1) || !vq->user_be; So if the endianness is not explicitly set to BE, it will be forced to LE (instead of native endian)? Won't that break userspace that does not yet use the new interface when CONFIG_VHOST_SET_ENDIAN_LEGACY is set? > +} > +#else > +static void vhost_init_is_le(struct vhost_virtqueue *vq) > +{ > + if (vhost_has_feature(vq, VIRTIO_F_VERSION_1)) > + vq->is_le = true; > +} > +#endif > + > int vhost_init_used(struct vhost_virtqueue *vq) > { > __virtio16 last_used_idx; > int r; > - if (!vq->private_data) > + if (!vq->private_data) { > + vq->is_le = virtio_legacy_is_little_endian(); > return 0; > + } > + > + vhost_init_is_le(vq); > > r = vhost_update_used_flags(vq); > if (r) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/