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

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

On Thu, Jul 30, 2020 at 04:07:31PM +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]. The fencing of legacy virtio devices is done in
> `vu_set_features_exec`.
> 
> [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>


Reviewed-by: Michael S. Tsirkin <mst@redhat.com>

> ---
>  contrib/libvhost-user/libvhost-user.c | 77 +++++++++++++++------------
>  1 file changed, 43 insertions(+), 34 deletions(-)
> 
> diff --git a/contrib/libvhost-user/libvhost-user.c b/contrib/libvhost-user/libvhost-user.c
> index 53f16bdf082c..e2238a0400c9 100644
> --- a/contrib/libvhost-user/libvhost-user.c
> +++ b/contrib/libvhost-user/libvhost-user.c
> @@ -42,6 +42,7 @@
>  
>  #include "qemu/atomic.h"
>  #include "qemu/osdep.h"
> +#include "qemu/bswap.h"
>  #include "qemu/memfd.h"
>  
>  #include "libvhost-user.h"
> @@ -539,6 +540,14 @@ vu_set_features_exec(VuDev *dev, VhostUserMsg *vmsg)
>      DPRINT("u64: 0x%016"PRIx64"\n", vmsg->payload.u64);
>  
>      dev->features = vmsg->payload.u64;
> +    if (!vu_has_feature(dev, VIRTIO_F_VERSION_1)) {
> +        /*
> +         * We only support devices conforming to VIRTIO 1.0 or
> +         * later
> +         */
> +        vu_panic(dev, "virtio legacy devices aren't supported by libvhost-user");
> +        return false;
> +    }
>  
>      if (!(dev->features & VHOST_USER_F_PROTOCOL_FEATURES)) {
>          vu_set_enable_all_rings(dev, true);
> @@ -1074,7 +1083,7 @@ vu_set_vring_addr_exec(VuDev *dev, VhostUserMsg *vmsg)
>          return false;
>      }
>  
> -    vq->used_idx = vq->vring.used->idx;
> +    vq->used_idx = lduw_le_p(&vq->vring.used->idx);
>  
>      if (vq->last_avail_idx != vq->used_idx) {
>          bool resume = dev->iface->queue_is_processed_in_order &&
> @@ -1191,7 +1200,7 @@ vu_check_queue_inflights(VuDev *dev, VuVirtq *vq)
>          return 0;
>      }
>  
> -    vq->used_idx = vq->vring.used->idx;
> +    vq->used_idx = lduw_le_p(&vq->vring.used->idx);
>      vq->resubmit_num = 0;
>      vq->resubmit_list = NULL;
>      vq->counter = 0;
> @@ -2021,13 +2030,13 @@ vu_queue_started(const VuDev *dev, const VuVirtq *vq)
>  static inline uint16_t
>  vring_avail_flags(VuVirtq *vq)
>  {
> -    return vq->vring.avail->flags;
> +    return lduw_le_p(&vq->vring.avail->flags);
>  }
>  
>  static inline uint16_t
>  vring_avail_idx(VuVirtq *vq)
>  {
> -    vq->shadow_avail_idx = vq->vring.avail->idx;
> +    vq->shadow_avail_idx = lduw_le_p(&vq->vring.avail->idx);
>  
>      return vq->shadow_avail_idx;
>  }
> @@ -2035,7 +2044,7 @@ vring_avail_idx(VuVirtq *vq)
>  static inline uint16_t
>  vring_avail_ring(VuVirtq *vq, int i)
>  {
> -    return vq->vring.avail->ring[i];
> +    return lduw_le_p(&vq->vring.avail->ring[i]);
>  }
>  
>  static inline uint16_t
> @@ -2123,12 +2132,12 @@ 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 (!(lduw_le_p(&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 = lduw_le_p(&desc[i].next);
>      /* Make sure compiler knows to grab that: we don't want it changing! */
>      smp_wmb();
>  
> @@ -2171,8 +2180,8 @@ 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 (lduw_le_p(&desc[i].flags) & VRING_DESC_F_INDIRECT) {
> +            if (ldl_le_p(&desc[i].len) % sizeof(struct vring_desc)) {
>                  vu_panic(dev, "Invalid size for indirect buffer table");
>                  goto err;
>              }
> @@ -2185,8 +2194,8 @@ 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 = ldq_le_p(&desc[i].addr);
> +            desc_len = ldl_le_p(&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 +2222,10 @@ 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 (lduw_le_p(&desc[i].flags) & VRING_DESC_F_WRITE) {
> +                in_total += ldl_le_p(&desc[i].len);
>              } else {
> -                out_total += desc[i].len;
> +                out_total += ldl_le_p(&desc[i].len);
>              }
>              if (in_total >= max_in_bytes && out_total >= max_out_bytes) {
>                  goto done;
> @@ -2367,7 +2376,7 @@ vring_used_flags_set_bit(VuVirtq *vq, int mask)
>  
>      flags = (uint16_t *)((char*)vq->vring.used +
>                           offsetof(struct vring_used, flags));
> -    *flags |= mask;
> +    stw_le_p(flags, lduw_le_p(flags) | mask);
>  }
>  
>  static inline void
> @@ -2377,7 +2386,7 @@ vring_used_flags_unset_bit(VuVirtq *vq, int mask)
>  
>      flags = (uint16_t *)((char*)vq->vring.used +
>                           offsetof(struct vring_used, flags));
> -    *flags &= ~mask;
> +    stw_le_p(flags, lduw_le_p(flags) & ~mask);
>  }
>  
>  static inline void
> @@ -2387,7 +2396,7 @@ vring_set_avail_event(VuVirtq *vq, uint16_t val)
>          return;
>      }
>  
> -    *((uint16_t *) &vq->vring.used->ring[vq->vring.num]) = val;
> +    stw_le_p(&vq->vring.used->ring[vq->vring.num], val);
>  }
>  
>  void
> @@ -2476,14 +2485,14 @@ 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 (lduw_le_p(&desc[i].flags) & VRING_DESC_F_INDIRECT) {
> +        if (ldl_le_p(&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 = ldq_le_p(&desc[i].addr);
> +        desc_len = ldl_le_p(&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 +2514,10 @@ 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 (lduw_le_p(&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);
> +                               ldq_le_p(&desc[i].addr), ldl_le_p(&desc[i].len));
>          } else {
>              if (in_num) {
>                  vu_panic(dev, "Incorrect order for descriptors");
> @@ -2516,7 +2525,7 @@ 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);
> +                               ldq_le_p(&desc[i].addr), ldl_le_p(&desc[i].len));
>          }
>  
>          /* If we've got too many, that implies a descriptor loop. */
> @@ -2712,14 +2721,14 @@ 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 (lduw_le_p(&desc[i].flags) & VRING_DESC_F_INDIRECT) {
> +        if (ldl_le_p(&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 = ldq_le_p(&desc[i].addr);
> +        desc_len = ldl_le_p(&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 +2754,9 @@ 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 (lduw_le_p(&desc[i].flags) & VRING_DESC_F_WRITE) {
> +            min = MIN(ldl_le_p(&desc[i].len), len);
> +            vu_log_write(dev, ldq_le_p(&desc[i].addr), min);
>              len -= min;
>          }
>  
> @@ -2772,15 +2781,15 @@ vu_queue_fill(VuDev *dev, VuVirtq *vq,
>  
>      idx = (idx + vq->used_idx) % vq->vring.num;
>  
> -    uelem.id = elem->index;
> -    uelem.len = len;
> +    stl_le_p(&uelem.id, elem->index);
> +    stl_le_p(&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;
> +    stw_le_p(&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