From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755423AbbDGQLe (ORCPT ); Tue, 7 Apr 2015 12:11:34 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58806 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753117AbbDGQLd (ORCPT ); Tue, 7 Apr 2015 12:11:33 -0400 Date: Tue, 7 Apr 2015 18:11:29 +0200 From: "Michael S. Tsirkin" To: Greg Kurz Cc: Rusty Russell , linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCH v3 7/7] vhost: feature to set the vring endianness Message-ID: <20150407175640-mutt-send-email-mst@redhat.com> References: <20150407120929.4213.8225.stgit@bahia.lab.toulouse-stg.fr.ibm.com> <20150407121557.4213.95569.stgit@bahia.lab.toulouse-stg.fr.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150407121557.4213.95569.stgit@bahia.lab.toulouse-stg.fr.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 07, 2015 at 02:19:31PM +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 ioctls introduced by this patch are for legacy only: virtio 1.0 > devices are returned EPERM. > > Signed-off-by: Greg Kurz > --- > drivers/vhost/Kconfig | 10 ++++++++ > drivers/vhost/vhost.c | 55 ++++++++++++++++++++++++++++++++++++++++++++ > drivers/vhost/vhost.h | 17 +++++++++++++- > include/uapi/linux/vhost.h | 5 ++++ > 4 files changed, 86 insertions(+), 1 deletion(-) > > Changes since v2: > - fixed typos in Kconfig description > - renamed vq->legacy_big_endian to vq->legacy_is_little_endian > - vq->legacy_is_little_endian reset to default in vhost_vq_reset() > - dropped VHOST_F_SET_ENDIAN_LEGACY feature > - dropped struct vhost_vring_endian from the user API (re-use > struct vhost_vring_state instead) > - added VHOST_GET_VRING_ENDIAN_LEGACY ioctl > - introduced more helpers and stubs to avoid polluting the code with ifdefs > > > diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig > index 017a1e8..0aec88c 100644 > --- a/drivers/vhost/Kconfig > +++ b/drivers/vhost/Kconfig > @@ -32,3 +32,13 @@ config VHOST > ---help--- > This option is selected by any driver which needs to access > the core of vhost. > + > +config VHOST_SET_ENDIAN_LEGACY > + bool "Cross-endian support for host kernel accelerator" > + default n > + ---help--- > + This option allows vhost to support guests with a different byte > + ordering from host. It is disabled by default since it adds overhead > + and it is only needed by a few platforms (powerpc and arm). > + > + If unsure, say "N". > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index 2ee2826..3529a3c 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -199,6 +199,7 @@ static void vhost_vq_reset(struct vhost_dev *dev, > vq->call = NULL; > vq->log_ctx = NULL; > vq->memory = NULL; > + vq->legacy_is_little_endian = virtio_legacy_is_little_endian(); > } > > static int vhost_worker(void *data) > @@ -630,6 +631,54 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m) > return 0; > } > > +#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY > +static long vhost_set_vring_endian_legacy(struct vhost_virtqueue *vq, > + void __user *argp) > +{ > + struct vhost_vring_state s; > + > + if (vhost_has_feature(vq, VIRTIO_F_VERSION_1)) > + return -EPERM; > + > + if (copy_from_user(&s, argp, sizeof(s))) > + return -EFAULT; > + > + vq->legacy_is_little_endian = !!s.num; > + return 0; > +} > + > +static long vhost_get_vring_endian_legacy(struct vhost_virtqueue *vq, > + u32 idx, > + void __user *argp) > +{ > + struct vhost_vring_state s = { > + .index = idx, > + .num = vq->legacy_is_little_endian > + }; > + > + if (vhost_has_feature(vq, VIRTIO_F_VERSION_1)) > + return -EPERM; > + > + if (copy_to_user(argp, &s, sizeof(s))) > + return -EFAULT; > + > + return 0; > +} > +#else > +static long vhost_set_vring_endian_legacy(struct vhost_virtqueue *vq, > + void __user *argp) > +{ > + return 0; > +} > + > +static long vhost_get_vring_endian_legacy(struct vhost_virtqueue *vq, > + u32 idx, > + void __user *argp) > +{ > + return 0; > +} > +#endif /* CONFIG_VHOST_SET_ENDIAN_LEGACY */ > + > long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp) > { > struct file *eventfp, *filep = NULL; > @@ -806,6 +855,12 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp) > } else > filep = eventfp; > break; > + case VHOST_SET_VRING_ENDIAN_LEGACY: > + r = vhost_set_vring_endian_legacy(vq, argp); > + break; > + case VHOST_GET_VRING_ENDIAN_LEGACY: > + r = vhost_get_vring_endian_legacy(vq, idx, argp); > + break; > default: > r = -ENOIOCTLCMD; > } > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h > index 4e9a186..981ba06 100644 > --- a/drivers/vhost/vhost.h > +++ b/drivers/vhost/vhost.h > @@ -106,6 +106,9 @@ struct vhost_virtqueue { > /* Log write descriptors */ > void __user *log_base; > struct vhost_log *log; > + > + /* We need to know the device endianness with legacy virtio. */ > + bool legacy_is_little_endian; > }; > > struct vhost_dev { > @@ -173,11 +176,23 @@ static inline bool vhost_has_feature(struct vhost_virtqueue *vq, int bit) > return vq->acked_features & (1ULL << bit); > } > > +#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY > +static inline bool vhost_legacy_is_little_endian(struct vhost_virtqueue *vq) > +{ > + return vq->legacy_is_little_endian; > +} > +#else > +static inline bool vhost_legacy_is_little_endian(struct vhost_virtqueue *vq) > +{ > + return virtio_legacy_is_little_endian(); > +} > +#endif > + > static inline bool vhost_is_little_endian(struct vhost_virtqueue *vq) > { > if (vhost_has_feature(vq, VIRTIO_F_VERSION_1)) > return true; > - return virtio_legacy_is_little_endian(); > + return vhost_legacy_is_little_endian(vq); > } > > /* Memory accessors */ > diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h > index bb6a5b4..1b01a72 100644 > --- a/include/uapi/linux/vhost.h > +++ b/include/uapi/linux/vhost.h > @@ -103,6 +103,11 @@ 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 endianness for the ring (legacy virtio only) */ > +/* num is 0 for big endian, other values mean little endian */ > +#define VHOST_SET_VRING_ENDIAN_LEGACY _IOW(VHOST_VIRTIO, 0x13, struct vhost_vring_state) > +#define VHOST_GET_VRING_ENDIAN_LEGACY _IOW(VHOST_VIRTIO, 0x14, struct vhost_vring_state) > + > /* The following ioctls use eventfd file descriptors to signal and poll > * for events. */ > So if the config feature is enabled, you actually check two things: 1. feature 2. ioctl Why not override is_le when we set VIRTIO_F_VERSION_1? I guess you are worried that setting a value and not being able to read it back is ugly. We can add a flag to track it though. So here's an idea I would probably rename to G/SET_BIG_ENDIAN then it's obvious it's legacy. And just document that it's ignored with VIRTIO_F_VERSION_1. make sure it's not changed when ring is running simply set vq->is_le correctly when we start/stop the device vq->is_le = vhost_has_feature(vq, VIRTIO_F_VERSION_1) || !vq->user_be; static inline bool vhost_is_little_endian(struct vhost_virtqueue *vq) { return vq->is_le; } -- MST