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 <gkurz@xxxxxxxxxxxxxxxxxx>
---
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. */
_______________________________________________
Virtualization mailing list
Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linuxfoundation.org/mailman/listinfo/virtualization
