Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753206AbbDHIXo (ORCPT ); Wed, 8 Apr 2015 04:23:44 -0400 Received: from e06smtp11.uk.ibm.com ([195.75.94.107]:39549 "EHLO e06smtp11.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751286AbbDHIXk (ORCPT ); Wed, 8 Apr 2015 04:23:40 -0400 Date: Wed, 8 Apr 2015 10:23:29 +0200 From: Greg Kurz To: "Michael S. Tsirkin" 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: <20150408102329.7f39e80d@bahia.local> In-Reply-To: <20150407155228.GA1907@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> <20150407155228.GA1907@redhat.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: 15040808-0041-0000-0000-000003FC2238 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7588 Lines: 237 On Tue, 7 Apr 2015 17:52:28 +0200 "Michael S. Tsirkin" wrote: > 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 > > EINVAL probably makes more sense? > I had choosen EPERM because the error isn't related to the arguments being passed by userspace. It simply does not make sense to set the vring endianness for a virtio 1.0 device. That being said, I am perfectly fine with EINVAL. :) > > --- > > 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; > > EINVAL probably makes more sense? But I'm not sure this > is helpful: one can set VIRTIO_F_VERSION_1 afterwards, > and your patch does not seem to detect this. > Yeah, when I dropped the *bogus* feature from v2, I forgot to patch VHOST_SET_FEATURES accordingly... But thinking about it now, the choice to error out when setting VIRTIO_F_VERSION_1 because cross-endian legacy was set before looks terrible... :-\ > > > > + > > + 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; > > +} > > Should be -ENOIOCTLCMD? > Sure. > > +#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; > > } > > I think we also want to forbid this with a running backend. > Yes. > > 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 */ > > I'd prefer 0 and 1, return EINVAL on other values. > Ok. > > +#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. */ > > > Thanks. -- Greg -- 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/