Re: [Qemu-devel] [PATCH] vhost-user: avoid misaligned access

[Zhoujian (jay)]

> -----Original Message-----
> From: Michael S. Tsirkin [mailto:address@hidden
> Sent: Saturday, March 17, 2018 2:20 AM
> To: address@hidden
> Cc: Zhoujian (jay) <address@hidden>
> Subject: [PATCH] vhost-user: avoid misaligned access
> 
> We can't pass a pointer to memory field directly since it's within a packed
> structure, so isn't aligned.
> Pass a pointer on stack and copy.
> 
> Fixes: 30c4cc7 ("vhost: used_memslots refactoring")
> Cc: Jay Zhou <address@hidden>
> Signed-off-by: Michael S. Tsirkin <address@hidden>
> ---
> 
> I had to apply this to fix make check errors with clang.
> Pls review, test and ack.
> 
> Thanks!
> 
>  hw/virtio/vhost-user.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c index
> c12fdd9..a44ee7f 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -396,6 +396,7 @@ static int vhost_user_set_mem_table_postcopy(struct
> vhost_dev *dev,
>      bool reply_supported = virtio_has_feature(dev->protocol_features,
> 
> VHOST_USER_PROTOCOL_F_REPLY_ACK);
>      VhostUserMsg msg_reply;
> +    VhostUserMemory memory = {};
>      int region_i, msg_i;
> 
>      VhostUserMsg msg = {
> @@ -407,10 +408,11 @@ static int vhost_user_set_mem_table_postcopy(struct
> vhost_dev *dev,
>          msg.hdr.flags |= VHOST_USER_NEED_REPLY_MASK;
>      }
> 
> -    if (vhost_user_prepare_msg(dev, &msg.payload.memory, fds) < 0) {
> +    if (vhost_user_prepare_msg(dev, &memory, fds) < 0) {
>          error_report("Failed preparing vhost-user memory table msg");
>          return -1;
>      }
> +    msg.payload.memory = memory;
> 
>      fd_num = msg.payload.memory.nregions;
> 
> @@ -549,16 +551,19 @@ static int vhost_user_set_mem_table(struct vhost_dev
> *dev,
>          .hdr.request = VHOST_USER_SET_MEM_TABLE,
>          .hdr.flags = VHOST_USER_VERSION,
>      };
> +    VhostUserMemory memory = {};
> 
>      if (reply_supported) {
>          msg.hdr.flags |= VHOST_USER_NEED_REPLY_MASK;
>      }
> 
> -    if (vhost_user_prepare_msg(dev, &msg.payload.memory, fds) < 0) {
> +    if (vhost_user_prepare_msg(dev, &memory, fds) < 0) {
>          error_report("Failed preparing vhost-user memory table msg");
>          return -1;
>      }
> 
> +    msg.payload.memory = memory;
> +
>      fd_num = msg.payload.memory.nregions;
> 
>      if (!fd_num) {
> @@ -1575,8 +1580,11 @@ static void vhost_user_set_used_memslots(struct
> vhost_dev *dev)  {
>      int fds[VHOST_MEMORY_MAX_NREGIONS];
>      VhostUserMsg msg;
> +    VhostUserMemory memory = {};
> +
> +    vhost_user_prepare_msg(dev, &memory, fds);
> 
> -    vhost_user_prepare_msg(dev, &msg.payload.memory, fds);
> +    msg.payload.memory = memory;
>  }

Hi Michael, here should be like this:


static void vhost_user_set_used_memslots(struct vhost_dev *dev)
 {
     int fds[VHOST_MEMORY_MAX_NREGIONS];
-    VhostUserMsg msg;
+    VhostUserMemory memory = {};
 
-    vhost_user_prepare_msg(dev, &msg.payload.memory, fds);
+    vhost_user_prepare_msg(dev, &memory, fds);
 }


Regards,
Jay

> 
>  const VhostOps user_ops = {
> --
> MST