Re: [PATCH v2] net/virtio-user: fix not working on 32-bit system

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

On Wed, Apr 19, 2017 at 02:30:33AM +0000, Jianfeng Tan wrote:
> virtio-user cannot work on 32-bit system as higher 32-bit of the
> addr field (64-bit) in the desc is filled with non-zero value
> which should not happen for a 32-bit system.
> 
> In case of virtio-user, we use buf_addr of mbuf to fill the
> virtqueue desc addr. This is a regression bug. For 32-bit system,
> the first 4 bytes of mbuf is buf_addr, with following 8 bytes for
> buf_phyaddr. With below wrong definition, both buf_addr and lower
> 4 bytes buf_phyaddr are obtained to fill the virtqueue desc.
>   #define VIRTIO_MBUF_ADDR(mb, vq) \
> 	(*(uint64_t *)((uintptr_t)(mb) + (vq)->offset))
> 
> Fixes: 25f80d108780 ("net/virtio: fix packet corruption")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
> ---
>  drivers/net/virtio/virtqueue.h | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h
> index f9e3736..2e67460 100644
> --- a/drivers/net/virtio/virtqueue.h
> +++ b/drivers/net/virtio/virtqueue.h
> @@ -69,10 +69,16 @@ struct rte_mbuf;
>  
>  #ifdef RTE_VIRTIO_USER
>  /**
> - * Return the physical address (or virtual address in case of
> - * virtio-user) of mbuf data buffer.
> + *
> + * Return the physical address of mbuf data buffer for virtio pci:
> + *  on 32-bit system, offset equals 4, return the second four bytes of mbuf;
> + *  on 64-bit system, offset equals 8, return the second eight bytes of mbuf.
> + * Return the virtual address of mbuf data buffer for virtio-user.
> + *  on 32-bit system, offset equals 0, return the first four bytes of mbuf;
> + *  on 64-bit system, offset equals 0, return the first eight bytes of mbuf;


I've expected it to be plain english, something like following:

    /*
     * Return the physical address (or virtual address in case of
     * virtio-user) of mbuf data buffer.
     *
     * The address is firstly casted to the word size (sizeof(uintptr_t))
     * before casting it to uint64_t. This is to make it work with different
     * combination of word size (64 bit and 32 bit) and virtio device
     * (virtio-pci and virtio-user).
     */

Okay to you?

	--yliu