Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755538AbbDUSZK (ORCPT ); Tue, 21 Apr 2015 14:25:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:35819 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753526AbbDUSZH (ORCPT ); Tue, 21 Apr 2015 14:25:07 -0400 Date: Tue, 21 Apr 2015 20:25:03 +0200 From: "Michael S. Tsirkin" To: Greg Kurz Cc: Rusty Russell , Cornelia Huck , 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: <20150421201636-mutt-send-email-mst@redhat.com> References: <20150410101500.31843.61248.stgit@bahia.local> <20150410101627.31843.21710.stgit@bahia.local> <20150421155753-mutt-send-email-mst@redhat.com> <20150421174820.78c150b7@bahia.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150421174820.78c150b7@bahia.local> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9673 Lines: 292 On Tue, Apr 21, 2015 at 05:48:20PM +0200, Greg Kurz wrote: > On Tue, 21 Apr 2015 16:04:23 +0200 > "Michael S. Tsirkin" wrote: > > > On Fri, Apr 10, 2015 at 12:19:16PM +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 ++++++the > > > drivers/vhost/vhost.c | 76 +++++++++++++++++++++++++++++++++++++++++++- > > > drivers/vhost/vhost.h | 12 +++++-- > > > include/uapi/linux/vhost.h | 9 +++++ > > > 4 files changed, 103 insertions(+), 4 deletions(-) > > > > > > Changes since v3: > > > - VHOST_SET_VRING_ENDIAN_LEGACY ioctl renamed to VHOST_SET_VRING_BIG_ENDIAN > > > - ioctl API is now: 0 for le, 1 for be, other values are EINVAL > > > - ioctl doesn't filter out modern devices > > > - ioctl stubs return ENOIOCTLCMD > > > - forbid endianness changes when vring is active > > > - logic now handled with vq->is_le and vq->user_be according to device > > > start/stop as suggested by Michael > > > > > > 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 > > > > I'd prefer namin this VHOST_CROSS_ENDIAN_LEGACY > > > > Yes, makes sense. I'll make sure most of the cross-endian changes are > easy to grep. > > > > + 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). > > > > and is only useful on a few platforms (powerpc and arm). > > > > "it" seems to refer to "overhead", which is rarely needed. > > needed is a bit too strong, you can always e.g. run virtio > > in userspace. > > > > My poor English again... it seems you understood what I wanted to > write though :) > > > > + > > > + If unsure, say "N". > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > > index 2ee2826..3eb756b 100644the > > > --- a/drivers/vhost/vhost.c > > > +++ b/drivers/vhost/vhost.c > > > @@ -199,6 +199,10 @@ static void vhost_vq_reset(struct vhost_dev *dev, > > > vq->call = NULL; > > > vq->log_ctx = NULL; > > > vq->memory = NULL; > > > + vq->is_le = virtio_legacy_is_little_endian(); > > > +#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY > > > + vq->user_be = !vq->is_le; > > > +#endif > > > > add a wrapper for this too? > > > > Will do. > > > > } > > > > > > static int vhost_worker(void *data) > > > @@ -630,6 +634,53 @@ 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_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) > > > > s.num & ~0x1 > > > > Since s.num is unsigned and I assume this won't change, what about > s.num > 1 as suggested by Cornelia ? I just tried and gcc optimizes s.num != 0 && s.num != 1 to s.num > 1 The former will be more readable once we replace 0 and 1 with defines. So ignore my advice, keep code as is but use defines. > > > > > + return -EINVAL; > > > + > > > + vq->user_be = s.num; > > > + > > > + return 0; > > > +} > > > + > > > +static long vhost_get_vring_big_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; > > > +} > > > +#else > > > +static long vhost_set_vring_big_endian(struct vhost_virtqueue *vq, > > > + int __user *argp) > > > +{ > > > + return -ENOIOCTLCMD; > > > +} > > > + > > > +static long vhost_get_vring_big_endian(struct vhost_virtqueue *vq, u32 idx, > > > + int __user *argp) > > > +{ > > > + return -ENOIOCTLCMD; > > > +} > > > +#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 +857,12 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp) > > > } else > > > filep = eventfp;the > > > break; > > > + case VHOST_SET_VRING_BIG_ENDIAN: > > > + r = vhost_set_vring_big_endian(vq, argp); > > > + break; > > > + case VHOST_GET_VRING_BIG_ENDIAN: > > > + r = vhost_get_vring_big_endian(vq, idx, argp); > > > + break; > > > default: > > > r = -ENOIOCTLCMD; > > > } > > > @@ -1040,12 +1097,29 @@ static int vhost_update_avail_event(struct vhost_virtqueue *vq, u16 avail_event) > > > 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; > > > +} > > > +#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 > > > + > > > > I'd prefer localizing ifdefery somewhere near top of file. > > > > Will do. > > > > 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) > > > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h > > > index 4e9a186..04b2add 100644 > > > --- a/drivers/vhost/vhost.h > > > +++ b/drivers/vhost/vhost.h > > > @@ -106,6 +106,14 @@ struct vhost_virtqueue { > > > /* Log write descriptors */ > > > void __user *log_base; > > > struct vhost_log *log; > > > + > > > + /* Ring endianness. Defaults to legacy native endianness. > > > + * Set to true when starting a modern virtio device. */ > > > + bool is_le; > > > +#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY > > > + /* Ring endianness requested by userspace for cross-endian support. */ > > > + bool user_be; > > > +#endif > > > }; > > > > > > struct vhost_dev { > > > @@ -175,9 +183,7 @@ static inline bool vhost_has_feature(struct vhost_virtqueue *vq, int bit) > > > > > > 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 vq->is_le; > > > } > > > > > > /* Memory accessors */ > > > diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h > > > index bb6a5b4..5cdebbc 100644 > > > --- a/include/uapi/linux/vhost.h > > > +++ b/include/uapi/linux/vhost.h > > > @@ -103,6 +103,15 @@ 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. This is a legacy only API that is simply > > > + * ignored when VIRTIO_F_VERSION_1 is set. > > > + * 0 to set to little-endian > > > + * 1 to set to big-endian > > > > How about defines for these? > > > > Ok. I'll put the defines here so that all the cross-endian stuff > lies in the same hunk. Is it ok for you ? Fine. > > > + * other values return EINVAL. Pls also add a note saying that not all kernel configurations support this ioctl, but all configurations that support SET also support GET. > > > + */ > > > +#define VHOST_SET_VRING_BIG_ENDIAN _IOW(VHOST_VIRTIO, 0x13, struct vhost_vring_state) > > > +#define VHOST_GET_VRING_BIG_ENDIAN _IOW(VHOST_VIRTIO, 0x14, struct vhost_vring_state) > > > + > > > /* The following ioctls use eventfd file descriptors to signal and poll > > > * for events. */ > > > > > I'm inclined to think VHOST_SET_VRING_ENDIAN is a slightly better name. What do you think? -- MST -- 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/