| Message ID | 20160113170941.23705.93915.stgit@bahia.huguette.org |
|---|---|
| State | Not Applicable, archived |
| Delegated to: | David Miller |
| Headers | show |
On Wed, 13 Jan 2016 18:09:41 +0100 Greg Kurz <gkurz@linux.vnet.ibm.com> wrote: > The default use case for vhost is when the host and the vring have the > same endianness (default native endianness). But there are cases where > they differ and vhost should byteswap when accessing the vring: > - the host is big endian and the vring comes from a virtio 1.0 device > which is always little endian > - the architecture is bi-endian and the vring comes from a legacy virtio > device with a different endianness than the endianness of the host (aka > legacy cross-endian) > > These cases are handled by the vq->is_le and the optional vq->user_be, > with the following logic: > - if none of the fields is enabled, vhost access the vring without byteswap > - if the vring is virtio 1.0 and the host is big endian, vq->is_le is > enabled to enforce little endian access to the vring > - if the vring is legacy cross-endian, userspace enables vq->user_be > to inform vhost about the vring endianness. This endianness is then > enforced for vring accesses through vq->is_le again > > The logic is unclear in the current code. > > This patch introduces helpers with explicit enable and disable semantics, > for better clarity. > > No behaviour change. > > Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com> > --- > drivers/vhost/vhost.c | 28 +++++++++++++++++++--------- > 1 file changed, 19 insertions(+), 9 deletions(-) Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
On Wed, Jan 13, 2016 at 06:09:41PM +0100, Greg Kurz wrote: > The default use case for vhost is when the host and the vring have the > same endianness (default native endianness). But there are cases where > they differ and vhost should byteswap when accessing the vring: > - the host is big endian and the vring comes from a virtio 1.0 device > which is always little endian > - the architecture is bi-endian and the vring comes from a legacy virtio > device with a different endianness than the endianness of the host (aka > legacy cross-endian) > > These cases are handled by the vq->is_le and the optional vq->user_be, > with the following logic: > - if none of the fields is enabled, vhost access the vring without byteswap > - if the vring is virtio 1.0 and the host is big endian, vq->is_le is > enabled to enforce little endian access to the vring > - if the vring is legacy cross-endian, userspace enables vq->user_be > to inform vhost about the vring endianness. This endianness is then > enforced for vring accesses through vq->is_le again > > The logic is unclear in the current code. > > This patch introduces helpers with explicit enable and disable semantics, > for better clarity. > > No behaviour change. > > Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com> > --- > drivers/vhost/vhost.c | 28 +++++++++++++++++++--------- > 1 file changed, 19 insertions(+), 9 deletions(-) > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index ad2146a9ab2d..e02e06755ab7 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -43,11 +43,16 @@ enum { > #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) > +static void vhost_disable_user_be(struct vhost_virtqueue *vq) > { > vq->user_be = !virtio_legacy_is_little_endian(); > } > Hmm this doesn't look like an improvement to me. What does it mean to disable big endian? Make it little endian? Existing reset seems to make sense. > +static void vhost_enable_user_be(struct vhost_virtqueue *vq, bool user_be) > +{ > + vq->user_be = user_be; > +} > + And this is maybe "init_user_be"? > static long vhost_set_vring_endian(struct vhost_virtqueue *vq, int __user *argp) > { > struct vhost_vring_state s; > @@ -62,7 +67,7 @@ static long vhost_set_vring_endian(struct vhost_virtqueue *vq, int __user *argp) > s.num != VHOST_VRING_BIG_ENDIAN) > return -EINVAL; > > - vq->user_be = s.num; > + vhost_enable_user_be(vq, !!s.num); > > return 0; > } > @@ -81,7 +86,7 @@ static long vhost_get_vring_endian(struct vhost_virtqueue *vq, u32 idx, > return 0; > } > > -static void vhost_init_is_le(struct vhost_virtqueue *vq) > +static void vhost_enable_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 Same thing really. I'd rather add "reset_is_le". > @@ -91,7 +96,7 @@ 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_vq_reset_user_be(struct vhost_virtqueue *vq) > +static void vhost_disable_user_be(struct vhost_virtqueue *vq) > { > } > > @@ -106,13 +111,18 @@ static long vhost_get_vring_endian(struct vhost_virtqueue *vq, u32 idx, > return -ENOIOCTLCMD; > } > > -static void vhost_init_is_le(struct vhost_virtqueue *vq) > +static void vhost_enable_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_disable_is_le(struct vhost_virtqueue *vq) > +{ > + vq->is_le = virtio_legacy_is_little_endian(); > +} > + > static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh, > poll_table *pt) > { > @@ -276,8 +286,8 @@ 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(); > - vhost_vq_reset_user_be(vq); > + vhost_disable_is_le(vq); > + vhost_disable_user_be(vq); > } > > static int vhost_worker(void *data) > @@ -1157,11 +1167,11 @@ int vhost_init_used(struct vhost_virtqueue *vq) > __virtio16 last_used_idx; > int r; > if (!vq->private_data) { > - vq->is_le = virtio_legacy_is_little_endian(); > + vhost_disable_is_le(vq); > return 0; > } > > - vhost_init_is_le(vq); > + vhost_enable_is_le(vq); > > r = vhost_update_used_flags(vq); > if (r)
On Wed, 10 Feb 2016 13:21:22 +0200 "Michael S. Tsirkin" <mst@redhat.com> wrote: > On Wed, Jan 13, 2016 at 06:09:41PM +0100, Greg Kurz wrote: > > The default use case for vhost is when the host and the vring have the > > same endianness (default native endianness). But there are cases where > > they differ and vhost should byteswap when accessing the vring: > > - the host is big endian and the vring comes from a virtio 1.0 device > > which is always little endian > > - the architecture is bi-endian and the vring comes from a legacy virtio > > device with a different endianness than the endianness of the host (aka > > legacy cross-endian) > > > > These cases are handled by the vq->is_le and the optional vq->user_be, > > with the following logic: > > - if none of the fields is enabled, vhost access the vring without byteswap > > - if the vring is virtio 1.0 and the host is big endian, vq->is_le is > > enabled to enforce little endian access to the vring > > - if the vring is legacy cross-endian, userspace enables vq->user_be > > to inform vhost about the vring endianness. This endianness is then > > enforced for vring accesses through vq->is_le again > > > > The logic is unclear in the current code. > > > > This patch introduces helpers with explicit enable and disable semantics, > > for better clarity. > > > > No behaviour change. > > > > Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com> > > --- > > drivers/vhost/vhost.c | 28 +++++++++++++++++++--------- > > 1 file changed, 19 insertions(+), 9 deletions(-) > > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > index ad2146a9ab2d..e02e06755ab7 100644 > > --- a/drivers/vhost/vhost.c > > +++ b/drivers/vhost/vhost.c > > @@ -43,11 +43,16 @@ enum { > > #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) > > +static void vhost_disable_user_be(struct vhost_virtqueue *vq) > > { > > vq->user_be = !virtio_legacy_is_little_endian(); > > } > > > > Hmm this doesn't look like an improvement to me. > What does it mean to disable big endian? Make it little endian? The default behavior for the device is native endian. The SET_VRING_ENDIAN ioctl is used to make the device big endian on little endian hosts, hence "enabling" cross-endian mode... > Existing reset seems to make sense. > ... and we "disable" cross-endian mode on reset. > > +static void vhost_enable_user_be(struct vhost_virtqueue *vq, bool user_be) > > +{ > > + vq->user_be = user_be; > > +} > > + > > And this is maybe "init_user_be"? > Anyway I don't mind changing the names to reset/init_user_be if you think it is clearer. > > static long vhost_set_vring_endian(struct vhost_virtqueue *vq, int __user *argp) > > { > > struct vhost_vring_state s; > > @@ -62,7 +67,7 @@ static long vhost_set_vring_endian(struct vhost_virtqueue *vq, int __user *argp) > > s.num != VHOST_VRING_BIG_ENDIAN) > > return -EINVAL; > > > > - vq->user_be = s.num; > > + vhost_enable_user_be(vq, !!s.num); > > > > return 0; > > } > > @@ -81,7 +86,7 @@ static long vhost_get_vring_endian(struct vhost_virtqueue *vq, u32 idx, > > return 0; > > } > > > > -static void vhost_init_is_le(struct vhost_virtqueue *vq) > > +static void vhost_enable_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 > > Same thing really. I'd rather add "reset_is_le". > > > @@ -91,7 +96,7 @@ 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_vq_reset_user_be(struct vhost_virtqueue *vq) > > +static void vhost_disable_user_be(struct vhost_virtqueue *vq) > > { > > } > > > > @@ -106,13 +111,18 @@ static long vhost_get_vring_endian(struct vhost_virtqueue *vq, u32 idx, > > return -ENOIOCTLCMD; > > } > > > > -static void vhost_init_is_le(struct vhost_virtqueue *vq) > > +static void vhost_enable_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_disable_is_le(struct vhost_virtqueue *vq) > > +{ > > + vq->is_le = virtio_legacy_is_little_endian(); > > +} > > + > > static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh, > > poll_table *pt) > > { > > @@ -276,8 +286,8 @@ 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(); > > - vhost_vq_reset_user_be(vq); > > + vhost_disable_is_le(vq); > > + vhost_disable_user_be(vq); > > } > > > > static int vhost_worker(void *data) > > @@ -1157,11 +1167,11 @@ int vhost_init_used(struct vhost_virtqueue *vq) > > __virtio16 last_used_idx; > > int r; > > if (!vq->private_data) { > > - vq->is_le = virtio_legacy_is_little_endian(); > > + vhost_disable_is_le(vq); > > return 0; > > } > > > > - vhost_init_is_le(vq); > > + vhost_enable_is_le(vq); > > > > r = vhost_update_used_flags(vq); > > if (r) >
On Wed, 10 Feb 2016 13:11:34 +0100 Greg Kurz <gkurz@linux.vnet.ibm.com> wrote: > On Wed, 10 Feb 2016 13:21:22 +0200 > "Michael S. Tsirkin" <mst@redhat.com> wrote: > > > On Wed, Jan 13, 2016 at 06:09:41PM +0100, Greg Kurz wrote: > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > > index ad2146a9ab2d..e02e06755ab7 100644 > > > --- a/drivers/vhost/vhost.c > > > +++ b/drivers/vhost/vhost.c > > > @@ -43,11 +43,16 @@ enum { > > > #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) > > > +static void vhost_disable_user_be(struct vhost_virtqueue *vq) > > > { > > > vq->user_be = !virtio_legacy_is_little_endian(); > > > } > > > > > > > Hmm this doesn't look like an improvement to me. > > What does it mean to disable big endian? Make it little endian? > > The default behavior for the device is native endian. > > The SET_VRING_ENDIAN ioctl is used to make the device big endian > on little endian hosts, hence "enabling" cross-endian mode... > > > Existing reset seems to make sense. > > > > ... and we "disable" cross-endian mode on reset. > > > > +static void vhost_enable_user_be(struct vhost_virtqueue *vq, bool user_be) > > > +{ > > > + vq->user_be = user_be; > > > +} > > > + > > > > And this is maybe "init_user_be"? > > > > Anyway I don't mind changing the names to reset/init_user_be if you think it > is clearer. FWIW, I find the enable/disable terminology less confusing.
On Wed, Feb 10, 2016 at 01:11:34PM +0100, Greg Kurz wrote: > On Wed, 10 Feb 2016 13:21:22 +0200 > "Michael S. Tsirkin" <mst@redhat.com> wrote: > > > On Wed, Jan 13, 2016 at 06:09:41PM +0100, Greg Kurz wrote: > > > The default use case for vhost is when the host and the vring have the > > > same endianness (default native endianness). But there are cases where > > > they differ and vhost should byteswap when accessing the vring: > > > - the host is big endian and the vring comes from a virtio 1.0 device > > > which is always little endian > > > - the architecture is bi-endian and the vring comes from a legacy virtio > > > device with a different endianness than the endianness of the host (aka > > > legacy cross-endian) > > > > > > These cases are handled by the vq->is_le and the optional vq->user_be, > > > with the following logic: > > > - if none of the fields is enabled, vhost access the vring without byteswap > > > - if the vring is virtio 1.0 and the host is big endian, vq->is_le is > > > enabled to enforce little endian access to the vring > > > - if the vring is legacy cross-endian, userspace enables vq->user_be > > > to inform vhost about the vring endianness. This endianness is then > > > enforced for vring accesses through vq->is_le again > > > > > > The logic is unclear in the current code. > > > > > > This patch introduces helpers with explicit enable and disable semantics, > > > for better clarity. > > > > > > No behaviour change. > > > > > > Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com> > > > --- > > > drivers/vhost/vhost.c | 28 +++++++++++++++++++--------- > > > 1 file changed, 19 insertions(+), 9 deletions(-) > > > > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > > index ad2146a9ab2d..e02e06755ab7 100644 > > > --- a/drivers/vhost/vhost.c > > > +++ b/drivers/vhost/vhost.c > > > @@ -43,11 +43,16 @@ enum { > > > #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) > > > +static void vhost_disable_user_be(struct vhost_virtqueue *vq) > > > { > > > vq->user_be = !virtio_legacy_is_little_endian(); > > > } > > > > > > > Hmm this doesn't look like an improvement to me. > > What does it mean to disable big endian? Make it little endian? > > The default behavior for the device is native endian. > > The SET_VRING_ENDIAN ioctl is used to make the device big endian > on little endian hosts, hence "enabling" cross-endian mode... > > > Existing reset seems to make sense. > > > > ... and we "disable" cross-endian mode on reset. OK but that's enable cross-endian. Not enable be. We could have something like vhost_disable_user_byte_swap though each time we try, the result makes my head hurt: "swap" is a relative thing and hard to keep track of. > > > +static void vhost_enable_user_be(struct vhost_virtqueue *vq, bool user_be) > > > +{ > > > + vq->user_be = user_be; > > > +} > > > + > > > > And this is maybe "init_user_be"? > > > > Anyway I don't mind changing the names to reset/init_user_be if you think it > is clearer. > > > > static long vhost_set_vring_endian(struct vhost_virtqueue *vq, int __user *argp) > > > { > > > struct vhost_vring_state s; > > > @@ -62,7 +67,7 @@ static long vhost_set_vring_endian(struct vhost_virtqueue *vq, int __user *argp) > > > s.num != VHOST_VRING_BIG_ENDIAN) > > > return -EINVAL; > > > > > > - vq->user_be = s.num; > > > + vhost_enable_user_be(vq, !!s.num); > > > > > > return 0; > > > } > > > @@ -81,7 +86,7 @@ static long vhost_get_vring_endian(struct vhost_virtqueue *vq, u32 idx, > > > return 0; > > > } > > > > > > -static void vhost_init_is_le(struct vhost_virtqueue *vq) > > > +static void vhost_enable_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 > > > > Same thing really. I'd rather add "reset_is_le". > > > > > @@ -91,7 +96,7 @@ 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_vq_reset_user_be(struct vhost_virtqueue *vq) > > > +static void vhost_disable_user_be(struct vhost_virtqueue *vq) > > > { > > > } > > > > > > @@ -106,13 +111,18 @@ static long vhost_get_vring_endian(struct vhost_virtqueue *vq, u32 idx, > > > return -ENOIOCTLCMD; > > > } > > > > > > -static void vhost_init_is_le(struct vhost_virtqueue *vq) > > > +static void vhost_enable_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_disable_is_le(struct vhost_virtqueue *vq) > > > +{ > > > + vq->is_le = virtio_legacy_is_little_endian(); > > > +} > > > + > > > static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh, > > > poll_table *pt) > > > { > > > @@ -276,8 +286,8 @@ 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(); > > > - vhost_vq_reset_user_be(vq); > > > + vhost_disable_is_le(vq); > > > + vhost_disable_user_be(vq); > > > } > > > > > > static int vhost_worker(void *data) > > > @@ -1157,11 +1167,11 @@ int vhost_init_used(struct vhost_virtqueue *vq) > > > __virtio16 last_used_idx; > > > int r; > > > if (!vq->private_data) { > > > - vq->is_le = virtio_legacy_is_little_endian(); > > > + vhost_disable_is_le(vq); > > > return 0; > > > } > > > > > > - vhost_init_is_le(vq); > > > + vhost_enable_is_le(vq); > > > > > > r = vhost_update_used_flags(vq); > > > if (r) > >
On Wed, 10 Feb 2016 17:08:52 +0200 "Michael S. Tsirkin" <mst@redhat.com> wrote: > On Wed, Feb 10, 2016 at 01:11:34PM +0100, Greg Kurz wrote: > > On Wed, 10 Feb 2016 13:21:22 +0200 > > "Michael S. Tsirkin" <mst@redhat.com> wrote: > > > > > On Wed, Jan 13, 2016 at 06:09:41PM +0100, Greg Kurz wrote: > > > > The default use case for vhost is when the host and the vring have the > > > > same endianness (default native endianness). But there are cases where > > > > they differ and vhost should byteswap when accessing the vring: > > > > - the host is big endian and the vring comes from a virtio 1.0 device > > > > which is always little endian > > > > - the architecture is bi-endian and the vring comes from a legacy virtio > > > > device with a different endianness than the endianness of the host (aka > > > > legacy cross-endian) > > > > > > > > These cases are handled by the vq->is_le and the optional vq->user_be, > > > > with the following logic: > > > > - if none of the fields is enabled, vhost access the vring without byteswap > > > > - if the vring is virtio 1.0 and the host is big endian, vq->is_le is > > > > enabled to enforce little endian access to the vring > > > > - if the vring is legacy cross-endian, userspace enables vq->user_be > > > > to inform vhost about the vring endianness. This endianness is then > > > > enforced for vring accesses through vq->is_le again > > > > > > > > The logic is unclear in the current code. > > > > > > > > This patch introduces helpers with explicit enable and disable semantics, > > > > for better clarity. > > > > > > > > No behaviour change. > > > > > > > > Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com> > > > > --- > > > > drivers/vhost/vhost.c | 28 +++++++++++++++++++--------- > > > > 1 file changed, 19 insertions(+), 9 deletions(-) > > > > > > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > > > index ad2146a9ab2d..e02e06755ab7 100644 > > > > --- a/drivers/vhost/vhost.c > > > > +++ b/drivers/vhost/vhost.c > > > > @@ -43,11 +43,16 @@ enum { > > > > #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) > > > > +static void vhost_disable_user_be(struct vhost_virtqueue *vq) > > > > { > > > > vq->user_be = !virtio_legacy_is_little_endian(); > > > > } > > > > > > > > > > Hmm this doesn't look like an improvement to me. > > > What does it mean to disable big endian? Make it little endian? > > > > The default behavior for the device is native endian. > > > > The SET_VRING_ENDIAN ioctl is used to make the device big endian > > on little endian hosts, hence "enabling" cross-endian mode... > > > > > Existing reset seems to make sense. > > > > > > > ... and we "disable" cross-endian mode on reset. > > OK but that's enable cross-endian. Not enable be. We could have > something like vhost_disable_user_byte_swap though each time we try, > the result makes my head hurt: "swap" is a relative thing and hard to > keep track of. > What about having something like below then ? vhost_enable_cross_endian_big() to be called on little endian hosts with big endian devices vhost_enable_cross_endian_little() to be called on big endian hosts with little endian devices vhost_disable_cross_endian() to go back to the native endian default > > > > +static void vhost_enable_user_be(struct vhost_virtqueue *vq, bool user_be) > > > > +{ > > > > + vq->user_be = user_be; > > > > +} > > > > + > > > > > > And this is maybe "init_user_be"? > > > > > > > Anyway I don't mind changing the names to reset/init_user_be if you think it > > is clearer. > > > > > > static long vhost_set_vring_endian(struct vhost_virtqueue *vq, int __user *argp) > > > > { > > > > struct vhost_vring_state s; > > > > @@ -62,7 +67,7 @@ static long vhost_set_vring_endian(struct vhost_virtqueue *vq, int __user *argp) > > > > s.num != VHOST_VRING_BIG_ENDIAN) > > > > return -EINVAL; > > > > > > > > - vq->user_be = s.num; > > > > + vhost_enable_user_be(vq, !!s.num); > > > > > > > > return 0; > > > > } > > > > @@ -81,7 +86,7 @@ static long vhost_get_vring_endian(struct vhost_virtqueue *vq, u32 idx, > > > > return 0; > > > > } > > > > > > > > -static void vhost_init_is_le(struct vhost_virtqueue *vq) > > > > +static void vhost_enable_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 > > > > > > Same thing really. I'd rather add "reset_is_le". > > > > > > > @@ -91,7 +96,7 @@ 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_vq_reset_user_be(struct vhost_virtqueue *vq) > > > > +static void vhost_disable_user_be(struct vhost_virtqueue *vq) > > > > { > > > > } > > > > > > > > @@ -106,13 +111,18 @@ static long vhost_get_vring_endian(struct vhost_virtqueue *vq, u32 idx, > > > > return -ENOIOCTLCMD; > > > > } > > > > > > > > -static void vhost_init_is_le(struct vhost_virtqueue *vq) > > > > +static void vhost_enable_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_disable_is_le(struct vhost_virtqueue *vq) > > > > +{ > > > > + vq->is_le = virtio_legacy_is_little_endian(); > > > > +} > > > > + > > > > static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh, > > > > poll_table *pt) > > > > { > > > > @@ -276,8 +286,8 @@ 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(); > > > > - vhost_vq_reset_user_be(vq); > > > > + vhost_disable_is_le(vq); > > > > + vhost_disable_user_be(vq); > > > > } > > > > > > > > static int vhost_worker(void *data) > > > > @@ -1157,11 +1167,11 @@ int vhost_init_used(struct vhost_virtqueue *vq) > > > > __virtio16 last_used_idx; > > > > int r; > > > > if (!vq->private_data) { > > > > - vq->is_le = virtio_legacy_is_little_endian(); > > > > + vhost_disable_is_le(vq); > > > > return 0; > > > > } > > > > > > > > - vhost_init_is_le(vq); > > > > + vhost_enable_is_le(vq); > > > > > > > > r = vhost_update_used_flags(vq); > > > > if (r) > > > >
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index ad2146a9ab2d..e02e06755ab7 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -43,11 +43,16 @@ enum { #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) +static void vhost_disable_user_be(struct vhost_virtqueue *vq) { vq->user_be = !virtio_legacy_is_little_endian(); } +static void vhost_enable_user_be(struct vhost_virtqueue *vq, bool user_be) +{ + vq->user_be = user_be; +} + static long vhost_set_vring_endian(struct vhost_virtqueue *vq, int __user *argp) { struct vhost_vring_state s; @@ -62,7 +67,7 @@ static long vhost_set_vring_endian(struct vhost_virtqueue *vq, int __user *argp) s.num != VHOST_VRING_BIG_ENDIAN) return -EINVAL; - vq->user_be = s.num; + vhost_enable_user_be(vq, !!s.num); return 0; } @@ -81,7 +86,7 @@ static long vhost_get_vring_endian(struct vhost_virtqueue *vq, u32 idx, return 0; } -static void vhost_init_is_le(struct vhost_virtqueue *vq) +static void vhost_enable_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 @@ -91,7 +96,7 @@ 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_vq_reset_user_be(struct vhost_virtqueue *vq) +static void vhost_disable_user_be(struct vhost_virtqueue *vq) { } @@ -106,13 +111,18 @@ static long vhost_get_vring_endian(struct vhost_virtqueue *vq, u32 idx, return -ENOIOCTLCMD; } -static void vhost_init_is_le(struct vhost_virtqueue *vq) +static void vhost_enable_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_disable_is_le(struct vhost_virtqueue *vq) +{ + vq->is_le = virtio_legacy_is_little_endian(); +} + static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh, poll_table *pt) { @@ -276,8 +286,8 @@ 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(); - vhost_vq_reset_user_be(vq); + vhost_disable_is_le(vq); + vhost_disable_user_be(vq); } static int vhost_worker(void *data) @@ -1157,11 +1167,11 @@ int vhost_init_used(struct vhost_virtqueue *vq) __virtio16 last_used_idx; int r; if (!vq->private_data) { - vq->is_le = virtio_legacy_is_little_endian(); + vhost_disable_is_le(vq); return 0; } - vhost_init_is_le(vq); + vhost_enable_is_le(vq); r = vhost_update_used_flags(vq); if (r)
The default use case for vhost is when the host and the vring have the same endianness (default native endianness). But there are cases where they differ and vhost should byteswap when accessing the vring: - the host is big endian and the vring comes from a virtio 1.0 device which is always little endian - the architecture is bi-endian and the vring comes from a legacy virtio device with a different endianness than the endianness of the host (aka legacy cross-endian) These cases are handled by the vq->is_le and the optional vq->user_be, with the following logic: - if none of the fields is enabled, vhost access the vring without byteswap - if the vring is virtio 1.0 and the host is big endian, vq->is_le is enabled to enforce little endian access to the vring - if the vring is legacy cross-endian, userspace enables vq->user_be to inform vhost about the vring endianness. This endianness is then enforced for vring accesses through vq->is_le again The logic is unclear in the current code. This patch introduces helpers with explicit enable and disable semantics, for better clarity. No behaviour change. Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com> --- drivers/vhost/vhost.c | 28 +++++++++++++++++++--------- 1 file changed, 19 insertions(+), 9 deletions(-)