# Re: \[PATCH\] vdpa/mlx5: Fix memory key MTT population

- From: Jason Wang \<hidden\>
- Date: 2021-01-07 04:17:51 
- List: virtualization
- Page: https://ratatoskr.run/virtualization/2021/01/6226113
- Thread: https://ratatoskr.run/netdev/2021/01/6225197/t.md

```text

On 2021/1/6 下午5:05, Eli Cohen wrote:
> map_direct_mr() assumed that the number of scatter/gather entries
> returned by dma_map_sg_attrs() was equal to the number of segments in
> the sgl list. This led to wrong population of the mkey object. Fix this
> by properly referring to the returned value.
>
> In addition, get rid of fill_sg() whjich effect is overwritten bu
> populate_mtts().


Typo.


>
> Fixes: 94abbccdf291 ("vdpa/mlx5: Add shared memory registration code")
> Signed-off-by: Eli Cohen <redacted>
> ---
>   drivers/vdpa/mlx5/core/mlx5_vdpa.h |  1 +
>   drivers/vdpa/mlx5/core/mr.c        | 28 ++++++++++++----------------
>   2 files changed, 13 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/vdpa/mlx5/core/mlx5_vdpa.h b/drivers/vdpa/mlx5/core/mlx5_vdpa.h
> index 5c92a576edae..08f742fd2409 100644
> --- a/drivers/vdpa/mlx5/core/mlx5_vdpa.h
> +++ b/drivers/vdpa/mlx5/core/mlx5_vdpa.h
> @@ -15,6 +15,7 @@ struct mlx5_vdpa_direct_mr {
>   	struct sg_table sg_head;
>   	int log_size;
>   	int nsg;
> +	int nent;
>   	struct list_head list;
>   	u64 offset;
>   };
> diff --git a/drivers/vdpa/mlx5/core/mr.c b/drivers/vdpa/mlx5/core/mr.c
> index 4b6195666c58..d300f799efcd 100644
> --- a/drivers/vdpa/mlx5/core/mr.c
> +++ b/drivers/vdpa/mlx5/core/mr.c
> @@ -25,17 +25,6 @@ static int get_octo_len(u64 len, int page_shift)
>   	return (npages + 1) / 2;
>   }
>   
> -static void fill_sg(struct mlx5_vdpa_direct_mr *mr, void *in)
> -{
> -	struct scatterlist *sg;
> -	__be64 *pas;
> -	int i;
> -
> -	pas = MLX5_ADDR_OF(create_mkey_in, in, klm_pas_mtt);
> -	for_each_sg(mr->sg_head.sgl, sg, mr->nsg, i)
> -		(*pas) = cpu_to_be64(sg_dma_address(sg));
> -}
> -
>   static void mlx5_set_access_mode(void *mkc, int mode)
>   {
>   	MLX5_SET(mkc, mkc, access_mode_1_0, mode & 0x3);
> @@ -45,10 +34,18 @@ static void mlx5_set_access_mode(void *mkc, int mode)
>   static void populate_mtts(struct mlx5_vdpa_direct_mr *mr, __be64 *mtt)
>   {
>   	struct scatterlist *sg;
> +	int nsg = mr->nsg;
> +	u64 dma_addr;
> +	u64 dma_len;
> +	int j = 0;
>   	int i;
>   
> -	for_each_sg(mr->sg_head.sgl, sg, mr->nsg, i)
> -		mtt[i] = cpu_to_be64(sg_dma_address(sg));
> +	for_each_sg(mr->sg_head.sgl, sg, mr->nent, i) {
> +		for (dma_addr = sg_dma_address(sg), dma_len = sg_dma_len(sg);
> +		     nsg && dma_len;
> +		     nsg--, dma_addr += BIT(mr->log_size), dma_len -= BIT(mr->log_size))
> +			mtt[j++] = cpu_to_be64(dma_addr);


It looks to me the mtt entry is also limited by log_size. It's better to explain this a little bit in the commit log.

Thanks


> +	}
>   }
>   
>   static int create_direct_mr(struct mlx5_vdpa_dev *mvdev, struct mlx5_vdpa_direct_mr *mr)
> @@ -64,7 +61,6 @@ static int create_direct_mr(struct mlx5_vdpa_dev *mvdev, struct mlx5_vdpa_direct
>   		return -ENOMEM;
>   
>   	MLX5_SET(create_mkey_in, in, uid, mvdev->res.uid);
> -	fill_sg(mr, in);
>   	mkc = MLX5_ADDR_OF(create_mkey_in, in, memory_key_mkey_entry);
>   	MLX5_SET(mkc, mkc, lw, !!(mr->perm & VHOST_MAP_WO));
>   	MLX5_SET(mkc, mkc, lr, !!(mr->perm & VHOST_MAP_RO));
> @@ -276,8 +272,8 @@ static int map_direct_mr(struct mlx5_vdpa_dev *mvdev, struct mlx5_vdpa_direct_mr
>   done:
>   	mr->log_size = log_entity_size;
>   	mr->nsg = nsg;
> -	err = dma_map_sg_attrs(dma, mr->sg_head.sgl, mr->nsg, DMA_BIDIRECTIONAL, 0);
> -	if (!err)
> +	mr->nent = dma_map_sg_attrs(dma, mr->sg_head.sgl, mr->nsg, DMA_BIDIRECTIONAL, 0);
> +	if (!mr->nent)
>   		goto err_map;
>   
>   	err = create_direct_mr(mvdev, mr);

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