Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965751AbbDXHTg (ORCPT ); Fri, 24 Apr 2015 03:19:36 -0400 Received: from e06smtp10.uk.ibm.com ([195.75.94.106]:56292 "EHLO e06smtp10.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965520AbbDXHTe (ORCPT ); Fri, 24 Apr 2015 03:19:34 -0400 Date: Fri, 24 Apr 2015 09:19:26 +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 v5 7/8] vhost: cross-endian support for legacy devices Message-ID: <20150424091926.1f5dee0b.cornelia.huck@de.ibm.com> In-Reply-To: <20150423152915.11795.13921.stgit@bahia.local> References: <20150423152608.11795.4373.stgit@bahia.local> <20150423152915.11795.13921.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: 15042407-0041-0000-0000-00000409A297 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6428 Lines: 194 On Thu, 23 Apr 2015 17:29:42 +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 > --- > > Changes since v4: > - rewrote patch title to mention cross-endian > - renamed config to VHOST_CROSS_ENDIAN_LEGACY > - rewrote config description and help > - moved ifdefery to top of vhost.c > - added a detailed comment about the lifecycle of vq->user_be in > vhost_init_is_le() > - renamed ioctls to VHOST_[GS]ET_VRING_ENDIAN > - added LE/BE defines to the ioctl API > - rewrote ioctl sanity check with the LE/BE defines > - updated comment in to mention that the availibility > of both SET and GET ioctls depends on the kernel config > > drivers/vhost/Kconfig | 15 ++++++++ > drivers/vhost/vhost.c | 86 +++++++++++++++++++++++++++++++++++++++++++- > drivers/vhost/vhost.h | 10 +++++ > include/uapi/linux/vhost.h | 12 ++++++ > 4 files changed, 121 insertions(+), 2 deletions(-) > > diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig > index 017a1e8..74d7380 100644 > --- a/drivers/vhost/Kconfig > +++ b/drivers/vhost/Kconfig > @@ -32,3 +32,18 @@ config VHOST > ---help--- > This option is selected by any driver which needs to access > the core of vhost. > + > +config VHOST_CROSS_ENDIAN_LEGACY > + bool "Cross-endian support for vhost" > + default n > + ---help--- > + This option allows vhost to support guests with a different byte > + ordering from host. "...while using legacy virtio." Might help to explain the "LEGACY" in the config option ;) > + > + Userspace programs can control the feature using the > + VHOST_SET_VRING_ENDIAN and VHOST_GET_VRING_ENDIAN ioctls. > + > + This is only useful on a few platforms (ppc64 and arm64). Since it > + adds some overhead, it is disabled default. s/default/by default/ > + > + If unsure, say "N". > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index 2ee2826..8c4390d 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -36,6 +36,78 @@ enum { > #define vhost_used_event(vq) ((__virtio16 __user *)&vq->avail->ring[vq->num]) > #define vhost_avail_event(vq) ((__virtio16 __user *)&vq->used->ring[vq->num]) > > +#ifdef CONFIG_VHOST_CROSS_ENDIAN_LEGACY > +static void vhost_vq_reset_user_be(struct vhost_virtqueue *vq) > +{ > + vq->user_be = !virtio_legacy_is_little_endian(); > +} > + > +static long vhost_set_vring_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 != VHOST_VRING_LITTLE_ENDIAN && > + s.num != VHOST_VRING_BIG_ENDIAN) > + return -EINVAL; > + > + vq->user_be = s.num; > + > + return 0; > +} > + > +static long vhost_get_vring_endian(struct vhost_virtqueue *vq, u32 idx, > + int __user *argp) > +{ > + struct vhost_vring_state s = { > + .index = idx, > + .num = vq->user_be > + }; > + > + if (copy_to_user(argp, &s, sizeof(s))) > + return -EFAULT; > + > + return 0; > +} > + > +static void vhost_init_is_le(struct vhost_virtqueue *vq) > +{ > + /* Note for legacy virtio: user_be is initialized at reset time > + * according to the host endianness. If userspace does not set an > + * explicit endianness, the default behavior is native endian, as > + * expected by legacy virtio. > + */ > + vq->is_le = vhost_has_feature(vq, VIRTIO_F_VERSION_1) || !vq->user_be; > +} > +#else > +static void vhost_vq_reset_user_be(struct vhost_virtqueue *vq) > +{ > + ; Just leave the function body empty? > +} > + > +static long vhost_set_vring_endian(struct vhost_virtqueue *vq, int __user *argp) > +{ > + return -ENOIOCTLCMD; > +} > + > +static long vhost_get_vring_endian(struct vhost_virtqueue *vq, u32 idx, > + int __user *argp) > +{ > + return -ENOIOCTLCMD; > +} > + > +static void vhost_init_is_le(struct vhost_virtqueue *vq) > +{ > + if (vhost_has_feature(vq, VIRTIO_F_VERSION_1)) > + vq->is_le = true; > +} > +#endif /* CONFIG_VHOST_CROSS_ENDIAN_LEGACY */ > + > static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh, > poll_table *pt) > { (...) > diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h > index bb6a5b4..b980b53 100644 > --- a/include/uapi/linux/vhost.h > +++ b/include/uapi/linux/vhost.h > @@ -103,6 +103,18 @@ struct vhost_memory { > /* Get accessor: reads index, writes value in num */ > #define VHOST_GET_VRING_BASE _IOWR(VHOST_VIRTIO, 0x12, struct vhost_vring_state) > > +/* Set the vring byte order in num. Valid values are VHOST_VRING_LITTLE_ENDIAN > + * or VHOST_VRING_BIG_ENDIAN (other values return EINVAL). -EINVAL? Should you also mention when you return -EBUSY? > + * This is a legacy only API that is simply ignored when VIRTIO_F_VERSION_1 is > + * set. > + * Not all kernel configurations support this ioctl, but all configurations that > + * support SET also support GET. > + */ > +#define VHOST_VRING_LITTLE_ENDIAN 0 > +#define VHOST_VRING_BIG_ENDIAN 1 > +#define VHOST_SET_VRING_ENDIAN _IOW(VHOST_VIRTIO, 0x13, struct vhost_vring_state) > +#define VHOST_GET_VRING_ENDIAN _IOW(VHOST_VIRTIO, 0x14, struct vhost_vring_state) > + > /* The following ioctls use eventfd file descriptors to signal and poll > * for events. */ Apart from style nitpicks, looks good. -- 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/