Re: [RFC v2 2/3] libvhost-user: handle endianness as mandated by the spec

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Jul 17, 2020 at 11:29:28AM +0200, Marc Hartmayer wrote:
> Since virtio existed even before it got standardized, the virtio
> standard defines the following types of virtio devices:
> 
>  + legacy device (pre-virtio 1.0)
>  + non-legacy or VIRTIO 1.0 device
>  + transitional device (which can act both as legacy and non-legacy)
> 
> Virtio 1.0 defines the fields of the virtqueues as little endian,
> while legacy uses guest's native endian [1]. Currently libvhost-user
> does not handle virtio endianness at all, i.e. it works only if the
> native endianness matches with whatever is actually needed. That means
> things break spectacularly on big-endian targets. Let us handle virtio
> endianness for non-legacy as required by the virtio specification
> [1]. We will fence non-legacy virtio devices with the upcoming patch.
> 
> [1] https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/virtio-v1.1-cs01.html#x1-210003
> 
> Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
> 
> ---
> Note: As we don't support legacy virtio devices

Who's "we" in this sentence? vhost user supports legacy generally ...

> there is dead code in
> libvhost-access.h that could be removed. But for the sake of
> completeness, I left it in the code.
> ---
>  contrib/libvhost-user/libvhost-access.h |  61 ++++++++++++
>  contrib/libvhost-user/libvhost-user.c   | 119 ++++++++++++------------
>  2 files changed, 121 insertions(+), 59 deletions(-)
>  create mode 100644 contrib/libvhost-user/libvhost-access.h
> 
> diff --git a/contrib/libvhost-user/libvhost-access.h b/contrib/libvhost-user/libvhost-access.h
> new file mode 100644
> index 000000000000..868ba3e7bfb8
> --- /dev/null
> +++ b/contrib/libvhost-user/libvhost-access.h
> @@ -0,0 +1,61 @@
> +#ifndef LIBVHOST_ACCESS_H
> +
> +#include "qemu/bswap.h"
> +
> +#include "libvhost-user.h"
> +
> +static inline bool vu_access_is_big_endian(VuDev *dev)
> +{
> +    /* Devices conforming to VIRTIO 1.0 or later are always LE. */
> +    return false;
> +}
> +
> +static inline void vu_stw_p(VuDev *vdev, void *ptr, uint16_t v)
> +{
> +    if (vu_access_is_big_endian(vdev)) {
> +        stw_be_p(ptr, v);
> +    } else {
> +        stw_le_p(ptr, v);
> +    }
> +}
> +
> +static inline void vu_stl_p(VuDev *vdev, void *ptr, uint32_t v)
> +{
> +    if (vu_access_is_big_endian(vdev)) {
> +        stl_be_p(ptr, v);
> +    } else {
> +        stl_le_p(ptr, v);
> +    }
> +}
> +
> +static inline void vu_stq_p(VuDev *vdev, void *ptr, uint64_t v)
> +{
> +    if (vu_access_is_big_endian(vdev)) {
> +        stq_be_p(ptr, v);
> +    } else {
> +        stq_le_p(ptr, v);
> +    }
> +}
> +
> +static inline int vu_lduw_p(VuDev *vdev, const void *ptr)
> +{
> +    if (vu_access_is_big_endian(vdev))
> +        return lduw_be_p(ptr);
> +    return lduw_le_p(ptr);
> +}
> +
> +static inline int vu_ldl_p(VuDev *vdev, const void *ptr)
> +{
> +    if (vu_access_is_big_endian(vdev))
> +        return ldl_be_p(ptr);
> +    return ldl_le_p(ptr);
> +}
> +
> +static inline uint64_t vu_ldq_p(VuDev *vdev, const void *ptr)
> +{
> +    if (vu_access_is_big_endian(vdev))
> +        return ldq_be_p(ptr);
> +    return ldq_le_p(ptr);
> +}
> +
> +#endif /* LIBVHOST_ACCESS_H */
> diff --git a/contrib/libvhost-user/libvhost-user.c b/contrib/libvhost-user/libvhost-user.c
> index d315db139606..0214b04c5291 100644
> --- a/contrib/libvhost-user/libvhost-user.c
> +++ b/contrib/libvhost-user/libvhost-user.c
> @@ -45,6 +45,7 @@
>  #include "qemu/memfd.h"
>  
>  #include "libvhost-user.h"
> +#include "libvhost-access.h"
>  
>  /* usually provided by GLib */
>  #ifndef MIN
> @@ -1074,7 +1075,7 @@ vu_set_vring_addr_exec(VuDev *dev, VhostUserMsg *vmsg)
>          return false;
>      }
>  
> -    vq->used_idx = vq->vring.used->idx;
> +    vq->used_idx = vu_lduw_p(dev, &vq->vring.used->idx);
>  
>      if (vq->last_avail_idx != vq->used_idx) {
>          bool resume = dev->iface->queue_is_processed_in_order &&
> @@ -1191,7 +1192,7 @@ vu_check_queue_inflights(VuDev *dev, VuVirtq *vq)
>          return 0;
>      }
>  
> -    vq->used_idx = vq->vring.used->idx;
> +    vq->used_idx = vu_lduw_p(dev, &vq->vring.used->idx);
>      vq->resubmit_num = 0;
>      vq->resubmit_list = NULL;
>      vq->counter = 0;
> @@ -2019,35 +2020,35 @@ vu_queue_started(const VuDev *dev, const VuVirtq *vq)
>  }
>  
>  static inline uint16_t
> -vring_avail_flags(VuVirtq *vq)
> +vring_avail_flags(VuDev *dev, VuVirtq *vq)
>  {
> -    return vq->vring.avail->flags;
> +    return vu_lduw_p(dev, &vq->vring.avail->flags);
>  }
>  
>  static inline uint16_t
> -vring_avail_idx(VuVirtq *vq)
> +vring_avail_idx(VuDev *dev, VuVirtq *vq)
>  {
> -    vq->shadow_avail_idx = vq->vring.avail->idx;
> +    vq->shadow_avail_idx = vu_lduw_p(dev, &vq->vring.avail->idx);
>  
>      return vq->shadow_avail_idx;
>  }
>  
>  static inline uint16_t
> -vring_avail_ring(VuVirtq *vq, int i)
> +vring_avail_ring(VuDev *dev, VuVirtq *vq, int i)
>  {
> -    return vq->vring.avail->ring[i];
> +    return vu_lduw_p(dev, &vq->vring.avail->ring[i]);
>  }
>  
>  static inline uint16_t
> -vring_get_used_event(VuVirtq *vq)
> +vring_get_used_event(VuDev *dev, VuVirtq *vq)
>  {
> -    return vring_avail_ring(vq, vq->vring.num);
> +    return vring_avail_ring(dev, vq, vq->vring.num);
>  }
>  
>  static int
>  virtqueue_num_heads(VuDev *dev, VuVirtq *vq, unsigned int idx)
>  {
> -    uint16_t num_heads = vring_avail_idx(vq) - idx;
> +    uint16_t num_heads = vring_avail_idx(dev, vq) - idx;
>  
>      /* Check it isn't doing very strange things with descriptor numbers. */
>      if (num_heads > vq->vring.num) {
> @@ -2070,7 +2071,7 @@ virtqueue_get_head(VuDev *dev, VuVirtq *vq,
>  {
>      /* Grab the next descriptor number they're advertising, and increment
>       * the index we've seen. */
> -    *head = vring_avail_ring(vq, idx % vq->vring.num);
> +    *head = vring_avail_ring(dev, vq, idx % vq->vring.num);
>  
>      /* If their number is silly, that's a fatal mistake. */
>      if (*head >= vq->vring.num) {
> @@ -2123,12 +2124,12 @@ virtqueue_read_next_desc(VuDev *dev, struct vring_desc *desc,
>                           int i, unsigned int max, unsigned int *next)
>  {
>      /* If this descriptor says it doesn't chain, we're done. */
> -    if (!(desc[i].flags & VRING_DESC_F_NEXT)) {
> +    if (!(vu_lduw_p(dev, &desc[i].flags) & VRING_DESC_F_NEXT)) {
>          return VIRTQUEUE_READ_DESC_DONE;
>      }
>  
>      /* Check they're not leading us off end of descriptors. */
> -    *next = desc[i].next;
> +    *next = vu_lduw_p(dev, &desc[i].next);
>      /* Make sure compiler knows to grab that: we don't want it changing! */
>      smp_wmb();
>  
> @@ -2171,8 +2172,8 @@ vu_queue_get_avail_bytes(VuDev *dev, VuVirtq *vq, unsigned int *in_bytes,
>          }
>          desc = vq->vring.desc;
>  
> -        if (desc[i].flags & VRING_DESC_F_INDIRECT) {
> -            if (desc[i].len % sizeof(struct vring_desc)) {
> +        if (vu_lduw_p(dev, &desc[i].flags) & VRING_DESC_F_INDIRECT) {
> +            if (vu_ldl_p(dev, &desc[i].len) % sizeof(struct vring_desc)) {
>                  vu_panic(dev, "Invalid size for indirect buffer table");
>                  goto err;
>              }
> @@ -2185,8 +2186,8 @@ vu_queue_get_avail_bytes(VuDev *dev, VuVirtq *vq, unsigned int *in_bytes,
>  
>              /* loop over the indirect descriptor table */
>              indirect = 1;
> -            desc_addr = desc[i].addr;
> -            desc_len = desc[i].len;
> +            desc_addr = vu_ldq_p(dev, &desc[i].addr);
> +            desc_len = vu_ldl_p(dev, &desc[i].len);
>              max = desc_len / sizeof(struct vring_desc);
>              read_len = desc_len;
>              desc = vu_gpa_to_va(dev, &read_len, desc_addr);
> @@ -2213,10 +2214,10 @@ vu_queue_get_avail_bytes(VuDev *dev, VuVirtq *vq, unsigned int *in_bytes,
>                  goto err;
>              }
>  
> -            if (desc[i].flags & VRING_DESC_F_WRITE) {
> -                in_total += desc[i].len;
> +            if (vu_lduw_p(dev, &desc[i].flags) & VRING_DESC_F_WRITE) {
> +                in_total += vu_ldl_p(dev, &desc[i].len);
>              } else {
> -                out_total += desc[i].len;
> +                out_total += vu_ldl_p(dev, &desc[i].len);
>              }
>              if (in_total >= max_in_bytes && out_total >= max_out_bytes) {
>                  goto done;
> @@ -2277,7 +2278,7 @@ vu_queue_empty(VuDev *dev, VuVirtq *vq)
>          return false;
>      }
>  
> -    return vring_avail_idx(vq) == vq->last_avail_idx;
> +    return vring_avail_idx(dev, vq) == vq->last_avail_idx;
>  }
>  
>  static bool
> @@ -2296,14 +2297,14 @@ vring_notify(VuDev *dev, VuVirtq *vq)
>      }
>  
>      if (!vu_has_feature(dev, VIRTIO_RING_F_EVENT_IDX)) {
> -        return !(vring_avail_flags(vq) & VRING_AVAIL_F_NO_INTERRUPT);
> +        return !(vring_avail_flags(dev, vq) & VRING_AVAIL_F_NO_INTERRUPT);
>      }
>  
>      v = vq->signalled_used_valid;
>      vq->signalled_used_valid = true;
>      old = vq->signalled_used;
>      new = vq->signalled_used = vq->used_idx;
> -    return !v || vring_need_event(vring_get_used_event(vq), new, old);
> +    return !v || vring_need_event(vring_get_used_event(dev, vq), new, old);
>  }
>  
>  static void _vu_queue_notify(VuDev *dev, VuVirtq *vq, bool sync)
> @@ -2361,33 +2362,33 @@ void vu_queue_notify_sync(VuDev *dev, VuVirtq *vq)
>  }
>  
>  static inline void
> -vring_used_flags_set_bit(VuVirtq *vq, int mask)
> +vring_used_flags_set_bit(VuDev *dev, VuVirtq *vq, int mask)
> +{
> +    uint16_t *flags;
> +
> +    flags = (uint16_t *)(char*)vq->vring.used +
> +        offsetof(struct vring_used, flags);
> +    vu_stw_p(dev, flags, vu_lduw_p(dev, flags) | mask);
> +}
> +
> +static inline void
> +vring_used_flags_unset_bit(VuDev *dev, VuVirtq *vq, int mask)
>  {
>      uint16_t *flags;
>  
>      flags = (uint16_t *)((char*)vq->vring.used +
>                           offsetof(struct vring_used, flags));
> -    *flags |= mask;
> +    vu_stw_p(dev, flags, vu_lduw_p(dev, flags) & ~mask);
>  }
>  
>  static inline void
> -vring_used_flags_unset_bit(VuVirtq *vq, int mask)
> -{
> -    uint16_t *flags;
> -
> -    flags = (uint16_t *)((char*)vq->vring.used +
> -                         offsetof(struct vring_used, flags));
> -    *flags &= ~mask;
> -}
> -
> -static inline void
> -vring_set_avail_event(VuVirtq *vq, uint16_t val)
> +vring_set_avail_event(VuDev *dev, VuVirtq *vq, uint16_t val)
>  {
>      if (!vq->notification) {
>          return;
>      }
>  
> -    *((uint16_t *) &vq->vring.used->ring[vq->vring.num]) = val;
> +    vu_stw_p(dev, &vq->vring.used->ring[vq->vring.num], val);
>  }
>  
>  void
> @@ -2395,11 +2396,11 @@ vu_queue_set_notification(VuDev *dev, VuVirtq *vq, int enable)
>  {
>      vq->notification = enable;
>      if (vu_has_feature(dev, VIRTIO_RING_F_EVENT_IDX)) {
> -        vring_set_avail_event(vq, vring_avail_idx(vq));
> +        vring_set_avail_event(dev, vq, vring_avail_idx(dev, vq));
>      } else if (enable) {
> -        vring_used_flags_unset_bit(vq, VRING_USED_F_NO_NOTIFY);
> +        vring_used_flags_unset_bit(dev, vq, VRING_USED_F_NO_NOTIFY);
>      } else {
> -        vring_used_flags_set_bit(vq, VRING_USED_F_NO_NOTIFY);
> +        vring_used_flags_set_bit(dev, vq, VRING_USED_F_NO_NOTIFY);
>      }
>      if (enable) {
>          /* Expose avail event/used flags before caller checks the avail idx. */
> @@ -2476,14 +2477,14 @@ vu_queue_map_desc(VuDev *dev, VuVirtq *vq, unsigned int idx, size_t sz)
>      struct vring_desc desc_buf[VIRTQUEUE_MAX_SIZE];
>      int rc;
>  
> -    if (desc[i].flags & VRING_DESC_F_INDIRECT) {
> -        if (desc[i].len % sizeof(struct vring_desc)) {
> +    if (vu_lduw_p(dev, &desc[i].flags) & VRING_DESC_F_INDIRECT) {
> +        if (vu_ldl_p(dev, &desc[i].len) % sizeof(struct vring_desc)) {
>              vu_panic(dev, "Invalid size for indirect buffer table");
>          }
>  
>          /* loop over the indirect descriptor table */
> -        desc_addr = desc[i].addr;
> -        desc_len = desc[i].len;
> +        desc_addr = vu_ldq_p(dev, &desc[i].addr);
> +        desc_len = vu_ldl_p(dev, &desc[i].len);
>          max = desc_len / sizeof(struct vring_desc);
>          read_len = desc_len;
>          desc = vu_gpa_to_va(dev, &read_len, desc_addr);
> @@ -2505,10 +2506,10 @@ vu_queue_map_desc(VuDev *dev, VuVirtq *vq, unsigned int idx, size_t sz)
>  
>      /* Collect all the descriptors */
>      do {
> -        if (desc[i].flags & VRING_DESC_F_WRITE) {
> +        if (vu_lduw_p(dev, &desc[i].flags) & VRING_DESC_F_WRITE) {
>              virtqueue_map_desc(dev, &in_num, iov + out_num,
>                                 VIRTQUEUE_MAX_SIZE - out_num, true,
> -                               desc[i].addr, desc[i].len);
> +                               vu_ldq_p(dev, &desc[i].addr), vu_ldl_p(dev, &desc[i].len));
>          } else {
>              if (in_num) {
>                  vu_panic(dev, "Incorrect order for descriptors");
> @@ -2516,7 +2517,7 @@ vu_queue_map_desc(VuDev *dev, VuVirtq *vq, unsigned int idx, size_t sz)
>              }
>              virtqueue_map_desc(dev, &out_num, iov,
>                                 VIRTQUEUE_MAX_SIZE, false,
> -                               desc[i].addr, desc[i].len);
> +                               vu_ldq_p(dev, &desc[i].addr), vu_ldl_p(dev, &desc[i].len));
>          }
>  
>          /* If we've got too many, that implies a descriptor loop. */
> @@ -2642,7 +2643,7 @@ vu_queue_pop(VuDev *dev, VuVirtq *vq, size_t sz)
>      }
>  
>      if (vu_has_feature(dev, VIRTIO_RING_F_EVENT_IDX)) {
> -        vring_set_avail_event(vq, vq->last_avail_idx);
> +        vring_set_avail_event(dev, vq, vq->last_avail_idx);
>      }
>  
>      elem = vu_queue_map_desc(dev, vq, head, sz);
> @@ -2712,14 +2713,14 @@ vu_log_queue_fill(VuDev *dev, VuVirtq *vq,
>      max = vq->vring.num;
>      i = elem->index;
>  
> -    if (desc[i].flags & VRING_DESC_F_INDIRECT) {
> -        if (desc[i].len % sizeof(struct vring_desc)) {
> +    if (vu_lduw_p(dev, &desc[i].flags) & VRING_DESC_F_INDIRECT) {
> +        if (vu_ldl_p(dev, &desc[i].len) % sizeof(struct vring_desc)) {
>              vu_panic(dev, "Invalid size for indirect buffer table");
>          }
>  
>          /* loop over the indirect descriptor table */
> -        desc_addr = desc[i].addr;
> -        desc_len = desc[i].len;
> +        desc_addr = vu_ldq_p(dev, &desc[i].addr);
> +        desc_len = vu_ldl_p(dev, &desc[i].len);
>          max = desc_len / sizeof(struct vring_desc);
>          read_len = desc_len;
>          desc = vu_gpa_to_va(dev, &read_len, desc_addr);
> @@ -2745,9 +2746,9 @@ vu_log_queue_fill(VuDev *dev, VuVirtq *vq,
>              return;
>          }
>  
> -        if (desc[i].flags & VRING_DESC_F_WRITE) {
> -            min = MIN(desc[i].len, len);
> -            vu_log_write(dev, desc[i].addr, min);
> +        if (vu_lduw_p(dev, &desc[i].flags) & VRING_DESC_F_WRITE) {
> +            min = MIN(vu_ldl_p(dev, &desc[i].len), len);
> +            vu_log_write(dev, vu_ldq_p(dev, &desc[i].addr), min);
>              len -= min;
>          }
>  
> @@ -2772,15 +2773,15 @@ vu_queue_fill(VuDev *dev, VuVirtq *vq,
>  
>      idx = (idx + vq->used_idx) % vq->vring.num;
>  
> -    uelem.id = elem->index;
> -    uelem.len = len;
> +    vu_stl_p(dev, &uelem.id, elem->index);
> +    vu_stl_p(dev, &uelem.len, len);
>      vring_used_write(dev, vq, &uelem, idx);
>  }
>  
>  static inline
>  void vring_used_idx_set(VuDev *dev, VuVirtq *vq, uint16_t val)
>  {
> -    vq->vring.used->idx = val;
> +    vu_stw_p(dev, &vq->vring.used->idx, val);
>      vu_log_write(dev,
>                   vq->vring.log_guest_addr + offsetof(struct vring_used, idx),
>                   sizeof(vq->vring.used->idx));
> -- 
> 2.25.4