Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755716AbbDXIGf (ORCPT ); Fri, 24 Apr 2015 04:06:35 -0400 Received: from e06smtp14.uk.ibm.com ([195.75.94.110]:44235 "EHLO e06smtp14.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752353AbbDXIGb (ORCPT ); Fri, 24 Apr 2015 04:06:31 -0400 Date: Fri, 24 Apr 2015 10:06:19 +0200 From: Greg Kurz To: Cornelia Huck 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: <20150424100619.665e8bf8@bahia.local> In-Reply-To: <20150424091926.1f5dee0b.cornelia.huck@de.ibm.com> References: <20150423152608.11795.4373.stgit@bahia.local> <20150423152915.11795.13921.stgit@bahia.local> <20150424091926.1f5dee0b.cornelia.huck@de.ibm.com> Organization: IBM X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.27; x86_64-redhat-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: 15042408-0017-0000-0000-000003D5C563 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7271 Lines: 224 On Fri, 24 Apr 2015 09:19:26 +0200 Cornelia Huck wrote: > 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 ;) > Makes sense indeed ! > > + > > + 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/ > Ok. > > + > > + 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? > Ok. > > +} > > + > > +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? > Oops, yes. :) > Should you also mention when you return -EBUSY? > Indeed... what about: "The byte order cannot be changed when the device is active: trying to do so returns -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. > Cool ! :) > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- 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/