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

[Eli Cohen <elic@nvidia.com>]

On Thu, Jan 07, 2021 at 12:15:53PM +0800, Jason Wang wrote:
> 
> 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.
> 
Will fix, thanks.
> 
> > 
> > Fixes: 94abbccdf291 ("vdpa/mlx5: Add shared memory registration code")
> > Signed-off-by: Eli Cohen <elic@nvidia.com>
> > ---
> >   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.

Actually, each MTT entry covers (1 << mr->log_size) contiguous memory.
I will add an explanation.

> 
> 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);
>