Subject: Re: [PATCH v5 4/4] RDMA/mlx5: get tph for p2p access when registering dma-buf mr

From: Alex Williamson <[email-masked]>
Date: Wed, 27 May 2026 13:00:45 -0600

On Tue, 26 May 2026 07:43:56 -0700
Zhiping Zhang <[email-masked]> wrote:

> Query dma-buf TPH metadata when registering a dma-buf MR for peer-to-
> peer access and translate the returned steering tag into an mlx5 ST
> index. Keep the DMAH path as the first priority and only fall back to
> DMA-buf metadata when no DMAH is supplied.
> 
> Track per-MR ownership of the allocated ST index and release it on MR
> setup failure, destroy, and FRMR-pool reuse. Release the ST index before
> the MR is pushed back into the FRMR pool, and free mlx5_st_idx_data when
> its refcount reaches zero so repeated allocation/deallocation does not
> leak memory.
> 
> Signed-off-by: Zhiping Zhang <[email-masked]>
> ---
>  drivers/infiniband/hw/mlx5/mlx5_ib.h          |  6 ++
>  drivers/infiniband/hw/mlx5/mr.c               | 86 ++++++++++++++++++-
>  .../net/ethernet/mellanox/mlx5/core/lib/st.c  | 28 ++++--
>  include/linux/mlx5/driver.h                   |  7 ++
>  4 files changed, 115 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/infiniband/hw/mlx5/mlx5_ib.h b/drivers/infiniband/hw/mlx5/mlx5_ib.h
> index e156dc4d7529..4ab867392267 100644
> --- a/drivers/infiniband/hw/mlx5/mlx5_ib.h
> +++ b/drivers/infiniband/hw/mlx5/mlx5_ib.h
> @@ -721,6 +721,12 @@ struct mlx5_ib_mr {
>  			u8 revoked :1;
>  			/* Indicates previous dmabuf page fault occurred */
>  			u8 dmabuf_faulted:1;
> +			/* Set when the MR owns dmabuf_st_index and must
> +			 * release it via mlx5_st_dealloc_index() once the
> +			 * firmware mkey is no longer referencing it.
> +			 */
> +			u8 dmabuf_st_owned:1;
> +			u16 dmabuf_st_index;
>  			struct mlx5_ib_mkey null_mmkey;
>  		};
>  	};
> diff --git a/drivers/infiniband/hw/mlx5/mr.c b/drivers/infiniband/hw/mlx5/mr.c
> index 3b6da45061a5..8059b5e4da97 100644
> --- a/drivers/infiniband/hw/mlx5/mr.c
> +++ b/drivers/infiniband/hw/mlx5/mr.c
> @@ -38,6 +38,7 @@
>  #include <linux/delay.h>
>  #include <linux/dma-buf.h>
>  #include <linux/dma-resv.h>
> +#include <linux/pci-tph.h>
>  #include <rdma/frmr_pools.h>
>  #include <rdma/ib_umem_odp.h>
>  #include "dm.h"
> @@ -46,6 +47,8 @@
>  #include "data_direct.h"
>  #include "dmah.h"
>  
> +MODULE_IMPORT_NS("DMA_BUF");
> +

This doesn't appear to add any dma-buf namespace dependencies.

>  static int mkey_max_umr_order(struct mlx5_ib_dev *dev)
>  {
>  	if (MLX5_CAP_GEN(dev->mdev, umr_extended_translation_offset))
> @@ -899,6 +902,63 @@ static struct dma_buf_attach_ops mlx5_ib_dmabuf_attach_ops = {
>  	.invalidate_mappings = mlx5_ib_dmabuf_invalidate_cb,
>  };
>  
> +/*
> + * Query TPH metadata from @dmabuf and translate the raw steering tag into
> + * an mlx5 ST index. On success, returns 0 and the caller becomes the
> + * owner of *@st_index (must be released with mlx5_st_dealloc_index()
> + * once the firmware mkey no longer references it). On any failure
> + * *@st_index and *@ph are left as the no-TPH defaults set by the caller.
> + *
> + * @dmabuf must already be referenced by the caller (e.g. via the umem's
> + * attachment) so we don't re-resolve the user's fd here and avoid a
> + * dup2() TOCTOU between umem creation and TPH lookup.
> + */
> +static void get_tph_mr_dmabuf(struct mlx5_ib_dev *dev, struct dma_buf *dmabuf,
> +			      u16 *st_index, u8 *ph)
> +{
> +	u8 req_type;
> +	u16 steering_tag;
> +	u8 st_width;
> +	int ret;
> +
> +	if (!dmabuf->ops->get_tph)
> +		return;
> +
> +	req_type = pcie_tph_enabled_req_type(dev->mdev->pdev);
> +	switch (req_type) {
> +	case PCI_TPH_REQ_TPH_ONLY:
> +		st_width = 8;
> +		break;
> +	case PCI_TPH_REQ_EXT_TPH:
> +		st_width = 16;
> +		break;
> +	default:
> +		return;
> +	}
> +
> +	ret = dmabuf->ops->get_tph(dmabuf, &steering_tag, ph, st_width);
> +	if (ret) {
> +		mlx5_ib_dbg(dev, "get_tph failed (%d)\n", ret);
> +		*ph = MLX5_IB_NO_PH;
> +		return;
> +	}
> +
> +	ret = mlx5_st_alloc_index_by_tag(dev->mdev, steering_tag, st_index);
> +	if (ret) {
> +		*ph = MLX5_IB_NO_PH;
> +		mlx5_ib_dbg(dev, "st_alloc_index_by_tag failed (%d)\n", ret);
> +	}
> +}

ph handling is inconsistent, why not use a local variable and only set
the caller's pointer on success?

> +
> +static void mlx5_ib_mr_put_dmabuf_st(struct mlx5_ib_mr *mr)
> +{
> +	if (mr->umem && mr->dmabuf_st_owned) {
> +		mlx5_st_dealloc_index(mr_to_mdev(mr)->mdev,
> +				      mr->dmabuf_st_index);
> +		mr->dmabuf_st_owned = 0;
> +	}
> +}
> +
>  static struct ib_mr *
>  reg_user_mr_dmabuf(struct ib_pd *pd, struct device *dma_device,
>  		   u64 offset, u64 length, u64 virt_addr,
> @@ -941,16 +1001,26 @@ reg_user_mr_dmabuf(struct ib_pd *pd, struct device *dma_device,
>  		ph = dmah->ph;
>  		if (dmah->valid_fields & BIT(IB_DMAH_CPU_ID_EXISTS))
>  			st_index = mdmah->st_index;
> +	} else {
> +		get_tph_mr_dmabuf(dev, umem_dmabuf->attach->dmabuf,
> +				  &st_index, &ph);
>  	}
>  
>  	mr = alloc_cacheable_mr(pd, &umem_dmabuf->umem, virt_addr,
>  				access_flags, access_mode,
>  				st_index, ph);
>  	if (IS_ERR(mr)) {
> +		if (!dmah && st_index != MLX5_MKC_PCIE_TPH_NO_STEERING_TAG_INDEX)
> +			mlx5_st_dealloc_index(dev->mdev, st_index);
>  		ib_umem_release(&umem_dmabuf->umem);
>  		return ERR_CAST(mr);
>  	}
>  
> +	if (!dmah && st_index != MLX5_MKC_PCIE_TPH_NO_STEERING_TAG_INDEX) {
> +		mr->dmabuf_st_index = st_index;
> +		mr->dmabuf_st_owned = 1;
> +	}
> +
>  	mlx5_ib_dbg(dev, "mkey 0x%x\n", mr->mmkey.key);
>  
>  	atomic_add(ib_umem_num_pages(mr->umem), &dev->mdev->priv.reg_pages);
> @@ -1377,9 +1447,17 @@ static int mlx5r_handle_mkey_cleanup(struct mlx5_ib_mr *mr)
>  	bool is_odp = is_odp_mr(mr);
>  	int ret;
>  
> -	if (mr->ibmr.frmr.pool && !mlx5_umr_revoke_mr_with_lock(mr) &&
> -	    !ib_frmr_pool_push(mr->ibmr.device, &mr->ibmr))
> -		return 0;
> +	if (mr->ibmr.frmr.pool && !mlx5_umr_revoke_mr_with_lock(mr)) {
> +		/*
> +		 * The mkey has been revoked: firmware no longer references
> +		 * dmabuf_st_index, so release it before this mr can re-enter
> +		 * the FRMR cache for reuse by another registration.
> +		 */
> +		mlx5_ib_mr_put_dmabuf_st(mr);
> +
> +		if (!ib_frmr_pool_push(mr->ibmr.device, &mr->ibmr))
> +			return 0;
> +	}
>  
>  	if (is_odp)
>  		mutex_lock(&to_ib_umem_odp(mr->umem)->umem_mutex);
> @@ -1400,6 +1478,8 @@ static int mlx5r_handle_mkey_cleanup(struct mlx5_ib_mr *mr)
>  		dma_resv_unlock(
>  			to_ib_umem_dmabuf(mr->umem)->attach->dmabuf->resv);
>  	}
> +	if (!ret)
> +		mlx5_ib_mr_put_dmabuf_st(mr);
>  	return ret;
>  }
>  
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lib/st.c b/drivers/net/ethernet/mellanox/mlx5/core/lib/st.c
> index 997be91f0a13..8929c17c88bc 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/lib/st.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/lib/st.c
> @@ -29,7 +29,7 @@ struct mlx5_st *mlx5_st_create(struct mlx5_core_dev *dev)
>  	u8 direct_mode = 0;
>  	u16 num_entries;
>  	u32 tbl_loc;
> -	int ret;
> +	int ret = 0;

Unnecessary change.

>  
>  	if (!MLX5_CAP_GEN(dev, mkey_pcie_tph))
>  		return NULL;
> @@ -92,23 +92,18 @@ void mlx5_st_destroy(struct mlx5_core_dev *dev)
>  	kfree(st);
>  }
>  
> -int mlx5_st_alloc_index(struct mlx5_core_dev *dev, enum tph_mem_type mem_type,
> -			unsigned int cpu_uid, u16 *st_index)
> +int mlx5_st_alloc_index_by_tag(struct mlx5_core_dev *dev, u16 tag,
> +			       u16 *st_index)
>  {
>  	struct mlx5_st_idx_data *idx_data;
>  	struct mlx5_st *st = dev->st;
>  	unsigned long index;
>  	u32 xa_id;
> -	u16 tag;
> -	int ret;
> +	int ret = 0;
>  
>  	if (!st)
>  		return -EOPNOTSUPP;
>  
> -	ret = pcie_tph_get_cpu_st(dev->pdev, mem_type, cpu_uid, &tag);
> -	if (ret)
> -		return ret;
> -
>  	if (st->direct_mode) {
>  		*st_index = tag;
>  		return 0;
> @@ -152,6 +147,20 @@ int mlx5_st_alloc_index(struct mlx5_core_dev *dev, enum tph_mem_type mem_type,
>  	mutex_unlock(&st->lock);
>  	return ret;
>  }
> +EXPORT_SYMBOL_GPL(mlx5_st_alloc_index_by_tag);
> +
> +int mlx5_st_alloc_index(struct mlx5_core_dev *dev, enum tph_mem_type mem_type,
> +			unsigned int cpu_uid, u16 *st_index)
> +{
> +	u16 tag;
> +	int ret;
> +
> +	ret = pcie_tph_get_cpu_st(dev->pdev, mem_type, cpu_uid, &tag);
> +	if (ret)
> +		return ret;
> +
> +	return mlx5_st_alloc_index_by_tag(dev, tag, st_index);
> +}
>  EXPORT_SYMBOL_GPL(mlx5_st_alloc_index);
>  
>  int mlx5_st_dealloc_index(struct mlx5_core_dev *dev, u16 st_index)
> @@ -175,6 +184,7 @@ int mlx5_st_dealloc_index(struct mlx5_core_dev *dev, u16 st_index)
>  
>  	if (refcount_dec_and_test(&idx_data->usecount)) {
>  		xa_erase(&st->idx_xa, st_index);
> +		kfree(idx_data);
>  		/* We leave PCI config space as was before, no mkey will refer to it */
>  	}

Should this be pulled out as a fix separate from the feature added
here?  Thanks,

Alex

>  
> diff --git a/include/linux/mlx5/driver.h b/include/linux/mlx5/driver.h
> index 04b96c5abb57..523a9ab0ae1e 100644
> --- a/include/linux/mlx5/driver.h
> +++ b/include/linux/mlx5/driver.h
> @@ -1166,10 +1166,17 @@ int mlx5_dm_sw_icm_dealloc(struct mlx5_core_dev *dev, enum mlx5_sw_icm_type type
>  			   u64 length, u16 uid, phys_addr_t addr, u32 obj_id);
>  
>  #ifdef CONFIG_PCIE_TPH
> +int mlx5_st_alloc_index_by_tag(struct mlx5_core_dev *dev, u16 tag,
> +			       u16 *st_index);
>  int mlx5_st_alloc_index(struct mlx5_core_dev *dev, enum tph_mem_type mem_type,
>  			unsigned int cpu_uid, u16 *st_index);
>  int mlx5_st_dealloc_index(struct mlx5_core_dev *dev, u16 st_index);
>  #else
> +static inline int mlx5_st_alloc_index_by_tag(struct mlx5_core_dev *dev,
> +					     u16 tag, u16 *st_index)
> +{
> +	return -EOPNOTSUPP;
> +}
>  static inline int mlx5_st_alloc_index(struct mlx5_core_dev *dev,
>  				      enum tph_mem_type mem_type,
>  				      unsigned int cpu_uid, u16 *st_index)