Michael S. Tsirkin
2015-Apr-02 14:20 UTC
[PATCH v2 7/7] vhost: feature to set the vring endianness
On Thu, Apr 02, 2015 at 03:17:13PM +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). > > If cross-endian support is compiled in, vhost abvertises a new feature > to be negotiated with userspace. If userspace acknowledges the feature, > it can inform vhost about the endianness to use with a new ioctl. > > This feature is mutually exclusive with virtio 1.0. Even if the vhost device > advertises virtio 1.0 and legacy cross-endian features, it cannot receive > aknowledgement for both at the same time. > > Hot paths are being preserved from any penalty when the config option is > disabled or when virtio 1.0 is being used. > > Signed-off-by: Greg Kurz <gkurz at linux.vnet.ibm.com> > --- > drivers/vhost/Kconfig | 10 ++++++++++ > drivers/vhost/net.c | 5 +++++ > drivers/vhost/scsi.c | 4 ++++ > drivers/vhost/test.c | 4 ++++ > drivers/vhost/vhost.c | 19 +++++++++++++++++++ > drivers/vhost/vhost.h | 13 ++++++++++++- > include/uapi/linux/vhost.h | 10 ++++++++++ > 7 files changed, 64 insertions(+), 1 deletion(-) > > diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig > index 017a1e8..5bb8da9 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 > + orderingfrom 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"."N"> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index 2bbfc25..5274a44 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -1011,6 +1011,11 @@ static int vhost_net_set_features(struct vhost_net *n, u64 features) > vhost_hlen = 0; > sock_hlen = hdr_len; > } > + > + if (features & ((1ULL << VHOST_F_SET_ENDIAN_LEGACY) | > + (1ULL << VIRTIO_F_VERSION_1))) > + return -EINVAL; > + > mutex_lock(&n->dev.mutex); > if ((features & (1 << VHOST_F_LOG_ALL)) && > !vhost_log_access_ok(&n->dev)) { > diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c > index 71df240..b53e9c2 100644 > --- a/drivers/vhost/scsi.c > +++ b/drivers/vhost/scsi.c > @@ -1544,6 +1544,10 @@ static int vhost_scsi_set_features(struct vhost_scsi *vs, u64 features) > if (features & ~VHOST_SCSI_FEATURES) > return -EOPNOTSUPP; > > + if (features & ((1ULL << VHOST_F_SET_ENDIAN_LEGACY) | > + (1ULL << VIRTIO_F_VERSION_1))) > + return -EINVAL; > + > mutex_lock(&vs->dev.mutex); > if ((features & (1 << VHOST_F_LOG_ALL)) && > !vhost_log_access_ok(&vs->dev)) { > diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c > index d9c501e..cfefdad 100644 > --- a/drivers/vhost/test.c > +++ b/drivers/vhost/test.c > @@ -243,6 +243,10 @@ static int vhost_test_set_features(struct vhost_test *n, u64 features) > { > struct vhost_virtqueue *vq; > > + if (features & ((1ULL << VHOST_F_SET_ENDIAN_LEGACY) | > + (1ULL << VIRTIO_F_VERSION_1))) > + return -EINVAL; > + > mutex_lock(&n->dev.mutex); > if ((features & (1 << VHOST_F_LOG_ALL)) && > !vhost_log_access_ok(&n->dev)) {Above seems to prevent users from specifying either VIRTIO_F_VERSION_1 or VHOST_F_SET_ENDIAN_LEGACY. Does it actually work?> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index 2ee2826..60a0f32 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_big_endian = false; > } > > static int vhost_worker(void *data) > @@ -806,6 +807,24 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp) > } else > filep = eventfp; > break; > +#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY > + case VHOST_SET_VRING_ENDIAN_LEGACY: > + { > + struct vhost_vring_endian e; > + > + if (!vhost_has_feature(vq, VHOST_F_SET_ENDIAN_LEGACY)) { > + r = -EINVAL; > + break; > + } > + > + if (copy_from_user(&e, argp, sizeof(e))) { > + r = -EFAULT; > + break; > + } > + vq->legacy_big_endian = e.is_big_endian; > + break; > + } > +#endif > default: > r = -ENOIOCTLCMD; > } > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h > index 4e9a186..d50881d 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_big_endian; > }; > > struct vhost_dev { > @@ -165,7 +168,11 @@ enum { > VHOST_FEATURES = (1ULL << VIRTIO_F_NOTIFY_ON_EMPTY) | > (1ULL << VIRTIO_RING_F_INDIRECT_DESC) | > (1ULL << VIRTIO_RING_F_EVENT_IDX) | > - (1ULL << VHOST_F_LOG_ALL), > + (1ULL << VHOST_F_LOG_ALL) | > +#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY > + (1ULL << VHOST_F_SET_ENDIAN_LEGACY) | > +#endif > + 0ULL, > }; > > static inline bool vhost_has_feature(struct vhost_virtqueue *vq, int bit) > @@ -177,6 +184,10 @@ static inline bool vhost_is_little_endian(struct vhost_virtqueue *vq) > { > if (vhost_has_feature(vq, VIRTIO_F_VERSION_1)) > return true; > +#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY > + if (vhost_has_feature(vq, VHOST_F_SET_ENDIAN_LEGACY)) > + return !vq->legacy_big_endian;why do we need to check the feature bit? How about simple return !vq->legacy_big_endian; here? All you need to do is set legacy_big_endian to !virtio_legacy_is_little_endian() on reset. Maybe rename to legacy_is_little_endian so you don't need to reverse the logic.> +#endif > return virtio_legacy_is_little_endian(); > } > > diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h > index bb6a5b4..09d2a48 100644 > --- a/include/uapi/linux/vhost.h > +++ b/include/uapi/linux/vhost.h > @@ -47,6 +47,11 @@ struct vhost_vring_addr { > __u64 log_guest_addr; > }; > > +struct vhost_vring_endian { > + unsigned int index; > + bool is_big_endian;bool in uapi is a bad idea. Generally, I think you can use vhost_vring_state here.> +}; > + > struct vhost_memory_region { > __u64 guest_phys_addr; > __u64 memory_size; /* bytes */ > @@ -103,6 +108,9 @@ 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) */ > +#define VHOST_SET_VRING_ENDIAN_LEGACY _IOW(VHOST_VIRTIO, 0x13, struct vhost_vring_endian) > + > /* The following ioctls use eventfd file descriptors to signal and poll > * for events. */ >You also need a GET ioctl, as a matter of policy.> @@ -126,6 +134,8 @@ struct vhost_memory { > #define VHOST_F_LOG_ALL 26 > /* vhost-net should add virtio_net_hdr for RX, and strip for TX packets. */ > #define VHOST_NET_F_VIRTIO_NET_HDR 27 > +/* the vring endianness can be explicitly set (legacy virtio only). */ > +#define VHOST_F_SET_ENDIAN_LEGACY 28 > > /* VHOST_SCSI specific definitions */VHOST_F_SET_ENDIAN_LEGACY doesn't seem too useful. Is this so userspace can detect kernel configuration? I think probing VHOST_SET_VRING_ENDIAN_LEGACY should be sufficient for this. -- MST
On Thu, 2 Apr 2015 16:20:46 +0200 "Michael S. Tsirkin" <mst at redhat.com> wrote:> On Thu, Apr 02, 2015 at 03:17:13PM +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). > > > > If cross-endian support is compiled in, vhost abvertises a new feature > > to be negotiated with userspace. If userspace acknowledges the feature, > > it can inform vhost about the endianness to use with a new ioctl. > > > > This feature is mutually exclusive with virtio 1.0. Even if the vhost device > > advertises virtio 1.0 and legacy cross-endian features, it cannot receive > > aknowledgement for both at the same time. > > > > Hot paths are being preserved from any penalty when the config option is > > disabled or when virtio 1.0 is being used. > > > > Signed-off-by: Greg Kurz <gkurz at linux.vnet.ibm.com> > > --- > > drivers/vhost/Kconfig | 10 ++++++++++ > > drivers/vhost/net.c | 5 +++++ > > drivers/vhost/scsi.c | 4 ++++ > > drivers/vhost/test.c | 4 ++++ > > drivers/vhost/vhost.c | 19 +++++++++++++++++++ > > drivers/vhost/vhost.h | 13 ++++++++++++- > > include/uapi/linux/vhost.h | 10 ++++++++++ > > 7 files changed, 64 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig > > index 017a1e8..5bb8da9 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". > > "N" > > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > > index 2bbfc25..5274a44 100644 > > --- a/drivers/vhost/net.c > > +++ b/drivers/vhost/net.c > > @@ -1011,6 +1011,11 @@ static int vhost_net_set_features(struct vhost_net *n, u64 features) > > vhost_hlen = 0; > > sock_hlen = hdr_len; > > } > > + > > + if (features & ((1ULL << VHOST_F_SET_ENDIAN_LEGACY) | > > + (1ULL << VIRTIO_F_VERSION_1))) > > + return -EINVAL; > > + > > mutex_lock(&n->dev.mutex); > > if ((features & (1 << VHOST_F_LOG_ALL)) && > > !vhost_log_access_ok(&n->dev)) { > > diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c > > index 71df240..b53e9c2 100644 > > --- a/drivers/vhost/scsi.c > > +++ b/drivers/vhost/scsi.c > > @@ -1544,6 +1544,10 @@ static int vhost_scsi_set_features(struct vhost_scsi *vs, u64 features) > > if (features & ~VHOST_SCSI_FEATURES) > > return -EOPNOTSUPP; > > > > + if (features & ((1ULL << VHOST_F_SET_ENDIAN_LEGACY) | > > + (1ULL << VIRTIO_F_VERSION_1))) > > + return -EINVAL; > > + > > mutex_lock(&vs->dev.mutex); > > if ((features & (1 << VHOST_F_LOG_ALL)) && > > !vhost_log_access_ok(&vs->dev)) { > > diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c > > index d9c501e..cfefdad 100644 > > --- a/drivers/vhost/test.c > > +++ b/drivers/vhost/test.c > > @@ -243,6 +243,10 @@ static int vhost_test_set_features(struct vhost_test *n, u64 features) > > { > > struct vhost_virtqueue *vq; > > > > + if (features & ((1ULL << VHOST_F_SET_ENDIAN_LEGACY) | > > + (1ULL << VIRTIO_F_VERSION_1))) > > + return -EINVAL; > > + > > mutex_lock(&n->dev.mutex); > > if ((features & (1 << VHOST_F_LOG_ALL)) && > > !vhost_log_access_ok(&n->dev)) { > > Above seems to prevent users from specifying either > VIRTIO_F_VERSION_1 or VHOST_F_SET_ENDIAN_LEGACY. > Does it actually work? >Arggg no it doesn't *of course*... I've added these bogus checks lately and didn't re-test :(> > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > index 2ee2826..60a0f32 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_big_endian = false; > > } > > > > static int vhost_worker(void *data) > > @@ -806,6 +807,24 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp) > > } else > > filep = eventfp; > > break; > > +#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY > > + case VHOST_SET_VRING_ENDIAN_LEGACY: > > + { > > + struct vhost_vring_endian e; > > + > > + if (!vhost_has_feature(vq, VHOST_F_SET_ENDIAN_LEGACY)) { > > + r = -EINVAL; > > + break; > > + } > > + > > + if (copy_from_user(&e, argp, sizeof(e))) { > > + r = -EFAULT; > > + break; > > + } > > + vq->legacy_big_endian = e.is_big_endian; > > + break; > > + } > > +#endif > > default: > > r = -ENOIOCTLCMD; > > } > > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h > > index 4e9a186..d50881d 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_big_endian; > > }; > > > > struct vhost_dev { > > @@ -165,7 +168,11 @@ enum { > > VHOST_FEATURES = (1ULL << VIRTIO_F_NOTIFY_ON_EMPTY) | > > (1ULL << VIRTIO_RING_F_INDIRECT_DESC) | > > (1ULL << VIRTIO_RING_F_EVENT_IDX) | > > - (1ULL << VHOST_F_LOG_ALL), > > + (1ULL << VHOST_F_LOG_ALL) | > > +#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY > > + (1ULL << VHOST_F_SET_ENDIAN_LEGACY) | > > +#endif > > + 0ULL, > > }; > > > > static inline bool vhost_has_feature(struct vhost_virtqueue *vq, int bit) > > @@ -177,6 +184,10 @@ static inline bool vhost_is_little_endian(struct vhost_virtqueue *vq) > > { > > if (vhost_has_feature(vq, VIRTIO_F_VERSION_1)) > > return true; > > +#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY > > + if (vhost_has_feature(vq, VHOST_F_SET_ENDIAN_LEGACY)) > > + return !vq->legacy_big_endian; > > why do we need to check the feature bit? > How about simple > return !vq->legacy_big_endian; > here?This is a runtime feature. Even for powerpc, cross-endian won't be the most common scenario. Userspace may have cleared the bit if it doesn't need/want it.> All you need to do is set legacy_big_endian to > !virtio_legacy_is_little_endian() on reset. > Maybe rename to legacy_is_little_endian so you don't > need to reverse the logic. >Do you mean vhost doesn't need userspace to provide the endianness to be used ? Please elaborate on the meaning of "reset" here... I am confused.> > +#endif > > return virtio_legacy_is_little_endian(); > > } > > > > diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h > > index bb6a5b4..09d2a48 100644 > > --- a/include/uapi/linux/vhost.h > > +++ b/include/uapi/linux/vhost.h > > @@ -47,6 +47,11 @@ struct vhost_vring_addr { > > __u64 log_guest_addr; > > }; > > > > +struct vhost_vring_endian { > > + unsigned int index; > > + bool is_big_endian; > > bool in uapi is a bad idea. > Generally, I think you can use vhost_vring_state here. >Ok to turn is_big_endian into an int but why hijacking vhost_vring_state ?> > +}; > > + > > struct vhost_memory_region { > > __u64 guest_phys_addr; > > __u64 memory_size; /* bytes */ > > @@ -103,6 +108,9 @@ 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) */ > > +#define VHOST_SET_VRING_ENDIAN_LEGACY _IOW(VHOST_VIRTIO, 0x13, struct vhost_vring_endian) > > + > > /* The following ioctls use eventfd file descriptors to signal and poll > > * for events. */ > > > > You also need a GET ioctl, as a matter of policy. >Ok. Will add.> > @@ -126,6 +134,8 @@ struct vhost_memory { > > #define VHOST_F_LOG_ALL 26 > > /* vhost-net should add virtio_net_hdr for RX, and strip for TX packets. */ > > #define VHOST_NET_F_VIRTIO_NET_HDR 27 > > +/* the vring endianness can be explicitly set (legacy virtio only). */ > > +#define VHOST_F_SET_ENDIAN_LEGACY 28 > > > > /* VHOST_SCSI specific definitions */ > > > VHOST_F_SET_ENDIAN_LEGACY doesn't seem too useful. > Is this so userspace can detect kernel configuration?Yes. Also, it is quite easy to "un-ack" the feature when it is not wanted.> I think probing VHOST_SET_VRING_ENDIAN_LEGACY should > be sufficient for this. >I'll get rid of the feature. Thanks for your time Michael. -- Greg
Michael S. Tsirkin
2015-Apr-02 18:53 UTC
[PATCH v2 7/7] vhost: feature to set the vring endianness
On Thu, Apr 02, 2015 at 06:45:27PM +0200, Greg Kurz wrote:> On Thu, 2 Apr 2015 16:20:46 +0200 > "Michael S. Tsirkin" <mst at redhat.com> wrote: > > > On Thu, Apr 02, 2015 at 03:17:13PM +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). > > > > > > If cross-endian support is compiled in, vhost abvertises a new feature > > > to be negotiated with userspace. If userspace acknowledges the feature, > > > it can inform vhost about the endianness to use with a new ioctl. > > > > > > This feature is mutually exclusive with virtio 1.0. Even if the vhost device > > > advertises virtio 1.0 and legacy cross-endian features, it cannot receive > > > aknowledgement for both at the same time. > > > > > > Hot paths are being preserved from any penalty when the config option is > > > disabled or when virtio 1.0 is being used. > > > > > > Signed-off-by: Greg Kurz <gkurz at linux.vnet.ibm.com> > > > --- > > > drivers/vhost/Kconfig | 10 ++++++++++ > > > drivers/vhost/net.c | 5 +++++ > > > drivers/vhost/scsi.c | 4 ++++ > > > drivers/vhost/test.c | 4 ++++ > > > drivers/vhost/vhost.c | 19 +++++++++++++++++++ > > > drivers/vhost/vhost.h | 13 ++++++++++++- > > > include/uapi/linux/vhost.h | 10 ++++++++++ > > > 7 files changed, 64 insertions(+), 1 deletion(-) > > > > > > diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig > > > index 017a1e8..5bb8da9 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". > > > > "N" > > > > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > > > index 2bbfc25..5274a44 100644 > > > --- a/drivers/vhost/net.c > > > +++ b/drivers/vhost/net.c > > > @@ -1011,6 +1011,11 @@ static int vhost_net_set_features(struct vhost_net *n, u64 features) > > > vhost_hlen = 0; > > > sock_hlen = hdr_len; > > > } > > > + > > > + if (features & ((1ULL << VHOST_F_SET_ENDIAN_LEGACY) | > > > + (1ULL << VIRTIO_F_VERSION_1))) > > > + return -EINVAL; > > > + > > > mutex_lock(&n->dev.mutex); > > > if ((features & (1 << VHOST_F_LOG_ALL)) && > > > !vhost_log_access_ok(&n->dev)) { > > > diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c > > > index 71df240..b53e9c2 100644 > > > --- a/drivers/vhost/scsi.c > > > +++ b/drivers/vhost/scsi.c > > > @@ -1544,6 +1544,10 @@ static int vhost_scsi_set_features(struct vhost_scsi *vs, u64 features) > > > if (features & ~VHOST_SCSI_FEATURES) > > > return -EOPNOTSUPP; > > > > > > + if (features & ((1ULL << VHOST_F_SET_ENDIAN_LEGACY) | > > > + (1ULL << VIRTIO_F_VERSION_1))) > > > + return -EINVAL; > > > + > > > mutex_lock(&vs->dev.mutex); > > > if ((features & (1 << VHOST_F_LOG_ALL)) && > > > !vhost_log_access_ok(&vs->dev)) { > > > diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c > > > index d9c501e..cfefdad 100644 > > > --- a/drivers/vhost/test.c > > > +++ b/drivers/vhost/test.c > > > @@ -243,6 +243,10 @@ static int vhost_test_set_features(struct vhost_test *n, u64 features) > > > { > > > struct vhost_virtqueue *vq; > > > > > > + if (features & ((1ULL << VHOST_F_SET_ENDIAN_LEGACY) | > > > + (1ULL << VIRTIO_F_VERSION_1))) > > > + return -EINVAL; > > > + > > > mutex_lock(&n->dev.mutex); > > > if ((features & (1 << VHOST_F_LOG_ALL)) && > > > !vhost_log_access_ok(&n->dev)) { > > > > Above seems to prevent users from specifying either > > VIRTIO_F_VERSION_1 or VHOST_F_SET_ENDIAN_LEGACY. > > Does it actually work? > > > > Arggg no it doesn't *of course*... I've added these bogus checks lately > and didn't re-test :(BTW I would be happier with less ifdefs all over the code, using some inline wrappers defined differently depending on ifdef. For example: #ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY bool vhost_vq_legacy_is_little_endian(vq) { return !vq->legacy_big_endian; } #else bool vhost_vq_legacy_is_little_endian(vq) { return virtio_legacy_is_little_endian(); } #endif similarly put VHOST_SET_VRING_ENDIAN_LEGACY handling in a separate function, with a stub definition when functionality is configured out.> > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > > index 2ee2826..60a0f32 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_big_endian = false; > > > } > > > > > > static int vhost_worker(void *data) > > > @@ -806,6 +807,24 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp) > > > } else > > > filep = eventfp; > > > break; > > > +#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY > > > + case VHOST_SET_VRING_ENDIAN_LEGACY: > > > + { > > > + struct vhost_vring_endian e; > > > + > > > + if (!vhost_has_feature(vq, VHOST_F_SET_ENDIAN_LEGACY)) { > > > + r = -EINVAL; > > > + break; > > > + } > > > + > > > + if (copy_from_user(&e, argp, sizeof(e))) { > > > + r = -EFAULT; > > > + break; > > > + } > > > + vq->legacy_big_endian = e.is_big_endian; > > > + break; > > > + } > > > +#endif > > > default: > > > r = -ENOIOCTLCMD; > > > } > > > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h > > > index 4e9a186..d50881d 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_big_endian; > > > }; > > > > > > struct vhost_dev { > > > @@ -165,7 +168,11 @@ enum { > > > VHOST_FEATURES = (1ULL << VIRTIO_F_NOTIFY_ON_EMPTY) | > > > (1ULL << VIRTIO_RING_F_INDIRECT_DESC) | > > > (1ULL << VIRTIO_RING_F_EVENT_IDX) | > > > - (1ULL << VHOST_F_LOG_ALL), > > > + (1ULL << VHOST_F_LOG_ALL) | > > > +#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY > > > + (1ULL << VHOST_F_SET_ENDIAN_LEGACY) | > > > +#endif > > > + 0ULL, > > > }; > > > > > > static inline bool vhost_has_feature(struct vhost_virtqueue *vq, int bit) > > > @@ -177,6 +184,10 @@ static inline bool vhost_is_little_endian(struct vhost_virtqueue *vq) > > > { > > > if (vhost_has_feature(vq, VIRTIO_F_VERSION_1)) > > > return true; > > > +#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY > > > + if (vhost_has_feature(vq, VHOST_F_SET_ENDIAN_LEGACY)) > > > + return !vq->legacy_big_endian; > > > > why do we need to check the feature bit? > > How about simple > > return !vq->legacy_big_endian; > > here? > > This is a runtime feature. Even for powerpc, cross-endian won't be the > most common scenario. Userspace may have cleared the bit if it doesn't > need/want it.Right but if we drop VHOST_F_SET_ENDIAN_LEGACY then it's simply #ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY return !vq->legacy_big_endian; #else return virtio_legacy_is_little_endian(); #endif> > All you need to do is set legacy_big_endian to > > !virtio_legacy_is_little_endian() on reset. > > Maybe rename to legacy_is_little_endian so you don't > > need to reverse the logic. > > > > Do you mean vhost doesn't need userspace to provide the endianness > to be used ? Please elaborate on the meaning of "reset" here... I > am confused.I refer to vhost_vq_reset here.> > > +#endif > > > return virtio_legacy_is_little_endian(); > > > } > > > > > > diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h > > > index bb6a5b4..09d2a48 100644 > > > --- a/include/uapi/linux/vhost.h > > > +++ b/include/uapi/linux/vhost.h > > > @@ -47,6 +47,11 @@ struct vhost_vring_addr { > > > __u64 log_guest_addr; > > > }; > > > > > > +struct vhost_vring_endian { > > > + unsigned int index; > > > + bool is_big_endian; > > > > bool in uapi is a bad idea. > > Generally, I think you can use vhost_vring_state here. > > > > Ok to turn is_big_endian into an int but why hijacking vhost_vring_state ?Yes.> > > > +}; > > > + > > > struct vhost_memory_region { > > > __u64 guest_phys_addr; > > > __u64 memory_size; /* bytes */ > > > @@ -103,6 +108,9 @@ 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) */ > > > +#define VHOST_SET_VRING_ENDIAN_LEGACY _IOW(VHOST_VIRTIO, 0x13, struct vhost_vring_endian) > > > + > > > /* The following ioctls use eventfd file descriptors to signal and poll > > > * for events. */ > > > > > > > You also need a GET ioctl, as a matter of policy. > > > > Ok. Will add. > > > > @@ -126,6 +134,8 @@ struct vhost_memory { > > > #define VHOST_F_LOG_ALL 26 > > > /* vhost-net should add virtio_net_hdr for RX, and strip for TX packets. */ > > > #define VHOST_NET_F_VIRTIO_NET_HDR 27 > > > +/* the vring endianness can be explicitly set (legacy virtio only). */ > > > +#define VHOST_F_SET_ENDIAN_LEGACY 28 > > > > > > /* VHOST_SCSI specific definitions */ > > > > > > VHOST_F_SET_ENDIAN_LEGACY doesn't seem too useful. > > Is this so userspace can detect kernel configuration? > > Yes. Also, it is quite easy to "un-ack" the feature when > it is not wanted. > > > I think probing VHOST_SET_VRING_ENDIAN_LEGACY should > > be sufficient for this. > > > > I'll get rid of the feature. > > Thanks for your time Michael. > > -- > Greg
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