Re: [PATCH v6 1/4] RDMA/umem: Support importing dma-buf as user memory region

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Oct 23, 2020 at 09:39:58AM -0700, Jianxin Xiong wrote:
> Dma-buf is a standard cross-driver buffer sharing mechanism that can be
> used to support peer-to-peer access from RDMA devices.
> 
> Device memory exported via dma-buf is associated with a file descriptor.
> This is passed to the user space as a property associated with the
> buffer allocation. When the buffer is registered as a memory region,
> the file descriptor is passed to the RDMA driver along with other
> parameters.
> 
> Implement the common code for importing dma-buf object and mapping
> dma-buf pages.
> 
> Signed-off-by: Jianxin Xiong <jianxin.xiong@intel.com>
> Reviewed-by: Sean Hefty <sean.hefty@intel.com>
> Acked-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
> Acked-by: Christian Koenig <christian.koenig@amd.com>
> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/infiniband/core/Makefile      |   2 +-
>  drivers/infiniband/core/umem.c        |   4 +
>  drivers/infiniband/core/umem_dmabuf.c | 197 ++++++++++++++++++++++++++++++++++
>  drivers/infiniband/core/umem_dmabuf.h |  11 ++
>  include/rdma/ib_umem.h                |  35 +++++-
>  5 files changed, 247 insertions(+), 2 deletions(-)
>  create mode 100644 drivers/infiniband/core/umem_dmabuf.c
>  create mode 100644 drivers/infiniband/core/umem_dmabuf.h
> 
> diff --git a/drivers/infiniband/core/Makefile b/drivers/infiniband/core/Makefile
> index ccf2670..8ab4eea 100644
> --- a/drivers/infiniband/core/Makefile
> +++ b/drivers/infiniband/core/Makefile
> @@ -40,5 +40,5 @@ ib_uverbs-y :=			uverbs_main.o uverbs_cmd.o uverbs_marshall.o \
>  				uverbs_std_types_srq.o \
>  				uverbs_std_types_wq.o \
>  				uverbs_std_types_qp.o
> -ib_uverbs-$(CONFIG_INFINIBAND_USER_MEM) += umem.o
> +ib_uverbs-$(CONFIG_INFINIBAND_USER_MEM) += umem.o umem_dmabuf.o
>  ib_uverbs-$(CONFIG_INFINIBAND_ON_DEMAND_PAGING) += umem_odp.o
> diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
> index e9fecbd..2c45525 100644
> --- a/drivers/infiniband/core/umem.c
> +++ b/drivers/infiniband/core/umem.c
> @@ -2,6 +2,7 @@
>   * Copyright (c) 2005 Topspin Communications.  All rights reserved.
>   * Copyright (c) 2005 Cisco Systems.  All rights reserved.
>   * Copyright (c) 2005 Mellanox Technologies. All rights reserved.
> + * Copyright (c) 2020 Intel Corporation. All rights reserved.
>   *
>   * This software is available to you under a choice of one of two
>   * licenses.  You may choose to be licensed under the terms of the GNU
> @@ -43,6 +44,7 @@
>  #include <rdma/ib_umem_odp.h>
>  
>  #include "uverbs.h"
> +#include "umem_dmabuf.h"
>  
>  static void __ib_umem_release(struct ib_device *dev, struct ib_umem *umem, int dirty)
>  {
> @@ -269,6 +271,8 @@ void ib_umem_release(struct ib_umem *umem)
>  {
>  	if (!umem)
>  		return;
> +	if (umem->is_dmabuf)
> +		return ib_umem_dmabuf_release(to_ib_umem_dmabuf(umem));
>  	if (umem->is_odp)
>  		return ib_umem_odp_release(to_ib_umem_odp(umem));
>  
> diff --git a/drivers/infiniband/core/umem_dmabuf.c b/drivers/infiniband/core/umem_dmabuf.c
> new file mode 100644
> index 0000000..66b234d
> --- /dev/null
> +++ b/drivers/infiniband/core/umem_dmabuf.c
> @@ -0,0 +1,197 @@
> +// SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause)
> +/*
> + * Copyright (c) 2020 Intel Corporation. All rights reserved.
> + */
> +
> +#include <linux/dma-buf.h>
> +#include <linux/dma-resv.h>
> +#include <linux/dma-mapping.h>
> +
> +#include "uverbs.h"
> +#include "umem_dmabuf.h"
> +
> +/*
> + * Generate a new dma sg list from a sub range of an existing dma sg list.
> + * Both the input and output have their entries page aligned.
> + */
> +static int ib_umem_dmabuf_sgt_slice(struct sg_table *sgt, u64 offset,
> +				    u64 length, struct sg_table *new_sgt)
> +{
> +	struct scatterlist *sg, *new_sg;
> +	u64 start, end, off, addr, len;
> +	unsigned int new_nents;
> +	int err;
> +	int i;
> +
> +	start = ALIGN_DOWN(offset, PAGE_SIZE);
> +	end = ALIGN(offset + length, PAGE_SIZE);
> +
> +	offset = start;
> +	length = end - start;
> +	new_nents = 0;
> +	for_each_sgtable_dma_sg(sgt, sg, i) {
> +		len = sg_dma_len(sg);
> +		off = min(len, offset);
> +		len -= off;
> +		len = min(len, length);
> +		if (len)
> +			new_nents++;
> +		length -= len;
> +		offset -= off;
> +	}
> +
> +	err = sg_alloc_table(new_sgt, new_nents, GFP_KERNEL);
> +	if (err)
> +		return err;
> +
> +	offset = start;
> +	length = end - start;
> +	new_sg = new_sgt->sgl;
> +	for_each_sgtable_dma_sg(sgt, sg, i) {
> +		addr = sg_dma_address(sg);
> +		len = sg_dma_len(sg);
> +		off = min(len, offset);
> +		addr += off;
> +		len -= off;
> +		len = min(len, length);
> +		if (len) {
> +			sg_dma_address(new_sg) = addr;
> +			sg_dma_len(new_sg) = len;
> +			new_sg = sg_next(new_sg);
> +		}
> +		length -= len;
> +		offset -= off;
> +	}
> +
> +	return 0;
> +}
> +
> +int ib_umem_dmabuf_map_pages(struct ib_umem_dmabuf *umem_dmabuf)
> +{
> +	struct sg_table *sgt;
> +	struct dma_fence *fence;
> +	int err;
> +
> +	dma_resv_assert_held(umem_dmabuf->attach->dmabuf->resv);
> +
> +	sgt = dma_buf_map_attachment(umem_dmabuf->attach,
> +				     DMA_BIDIRECTIONAL);
> +
> +	if (IS_ERR(sgt))
> +		return PTR_ERR(sgt);
> +
> +	err = ib_umem_dmabuf_sgt_slice(sgt, umem_dmabuf->umem.address,
> +				       umem_dmabuf->umem.length,
> +				       &umem_dmabuf->umem.sg_head);
> +	if (err) {
> +		dma_buf_unmap_attachment(umem_dmabuf->attach, sgt,
> +					 DMA_BIDIRECTIONAL);
> +		return err;
> +	}
> +
> +	umem_dmabuf->umem.nmap = umem_dmabuf->umem.sg_head.nents;
> +	umem_dmabuf->sgt = sgt;
> +
> +	/*
> +	 * Although the sg list is valid now, the content of the pages
> +	 * may be not up-to-date. Wait for the exporter to finish
> +	 * the migration.
> +	 */
> +	fence = dma_resv_get_excl(umem_dmabuf->attach->dmabuf->resv);
> +	if (fence)
> +		dma_fence_wait(fence, false);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(ib_umem_dmabuf_map_pages);
> +
> +void ib_umem_dmabuf_unmap_pages(struct ib_umem_dmabuf *umem_dmabuf)
> +{
> +	dma_resv_assert_held(umem_dmabuf->attach->dmabuf->resv);
> +
> +	if (!umem_dmabuf->sgt)
> +		return;
> +
> +	sg_free_table(&umem_dmabuf->umem.sg_head);
> +	dma_buf_unmap_attachment(umem_dmabuf->attach, umem_dmabuf->sgt,
> +				 DMA_BIDIRECTIONAL);
> +	umem_dmabuf->sgt = NULL;
> +}
> +EXPORT_SYMBOL(ib_umem_dmabuf_unmap_pages);
> +
> +struct ib_umem *ib_umem_dmabuf_get(struct ib_device *device,
> +				   unsigned long offset, size_t size,
> +				   int fd, int access,
> +				   const struct dma_buf_attach_ops *ops)
> +{
> +	struct dma_buf *dmabuf;
> +	struct ib_umem_dmabuf *umem_dmabuf;
> +	struct ib_umem *umem;
> +	unsigned long end;
> +	long ret;
> +
> +	if (check_add_overflow(offset, (unsigned long)size, &end))
> +		return ERR_PTR(-EINVAL);
> +
> +	if (unlikely(PAGE_ALIGN(end) < PAGE_SIZE))
> +		return ERR_PTR(-EINVAL);
> +
> +	if (unlikely(!ops || !ops->move_notify))
> +		return ERR_PTR(-EINVAL);
> +
> +#ifdef CONFIG_DMA_VIRT_OPS
> +	if (device->dma_device->dma_ops == &dma_virt_ops)
> +		return ERR_PTR(-EINVAL);
> +#endif

Maybe I'm confused, but should we have this check in dma_buf_attach, or at
least in dma_buf_dynamic_attach? The p2pdma functions use that too, and I
can't imagine how zerocopy should work (which is like the entire point of
dma-buf) when we have dma_virt_ops.

A similar problem exists for swiotlb bounce buffers, not sure how that's
solved.
-Daniel

> +
> +	umem_dmabuf = kzalloc(sizeof(*umem_dmabuf), GFP_KERNEL);
> +	if (!umem_dmabuf)
> +		return ERR_PTR(-ENOMEM);
> +
> +	umem = &umem_dmabuf->umem;
> +	umem->ibdev = device;
> +	umem->length = size;
> +	umem->address = offset;
> +	umem->iova = offset;
> +	umem->writable = ib_access_writable(access);
> +	umem->is_dmabuf = 1;
> +
> +	dmabuf = dma_buf_get(fd);
> +	if (IS_ERR(dmabuf)) {
> +		ret = PTR_ERR(dmabuf);
> +		goto out_free_umem;
> +	}
> +
> +	umem_dmabuf->attach = dma_buf_dynamic_attach(
> +					dmabuf,
> +					device->dma_device,
> +					ops,
> +					umem_dmabuf);
> +	if (IS_ERR(umem_dmabuf->attach)) {
> +		ret = PTR_ERR(umem_dmabuf->attach);
> +		goto out_release_dmabuf;
> +	}
> +
> +	return umem;
> +
> +out_release_dmabuf:
> +	dma_buf_put(dmabuf);
> +
> +out_free_umem:
> +	kfree(umem_dmabuf);
> +	return ERR_PTR(ret);
> +}
> +EXPORT_SYMBOL(ib_umem_dmabuf_get);
> +
> +void ib_umem_dmabuf_release(struct ib_umem_dmabuf *umem_dmabuf)
> +{
> +	struct dma_buf *dmabuf = umem_dmabuf->attach->dmabuf;
> +
> +	dma_resv_lock(dmabuf->resv, NULL);
> +	ib_umem_dmabuf_unmap_pages(umem_dmabuf);
> +	dma_resv_unlock(dmabuf->resv);
> +
> +	dma_buf_detach(dmabuf, umem_dmabuf->attach);
> +	dma_buf_put(dmabuf);
> +	kfree(umem_dmabuf);
> +}
> diff --git a/drivers/infiniband/core/umem_dmabuf.h b/drivers/infiniband/core/umem_dmabuf.h
> new file mode 100644
> index 0000000..13acf55
> --- /dev/null
> +++ b/drivers/infiniband/core/umem_dmabuf.h
> @@ -0,0 +1,11 @@
> +/* SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause) */
> +/*
> + * Copyright (c) 2020 Intel Corporation. All rights reserved.
> + */
> +
> +#ifndef UMEM_DMABUF_H
> +#define UMEM_DMABUF_H
> +
> +void ib_umem_dmabuf_release(struct ib_umem_dmabuf *umem_dmabuf);
> +
> +#endif /* UMEM_DMABUF_H */
> diff --git a/include/rdma/ib_umem.h b/include/rdma/ib_umem.h
> index 7059750..73a7b19 100644
> --- a/include/rdma/ib_umem.h
> +++ b/include/rdma/ib_umem.h
> @@ -1,6 +1,7 @@
>  /* SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB */
>  /*
>   * Copyright (c) 2007 Cisco Systems.  All rights reserved.
> + * Copyright (c) 2020 Intel Corporation.  All rights reserved.
>   */
>  
>  #ifndef IB_UMEM_H
> @@ -13,6 +14,7 @@
>  
>  struct ib_ucontext;
>  struct ib_umem_odp;
> +struct dma_buf_attach_ops;
>  
>  struct ib_umem {
>  	struct ib_device       *ibdev;
> @@ -22,12 +24,25 @@ struct ib_umem {
>  	unsigned long		address;
>  	u32 writable : 1;
>  	u32 is_odp : 1;
> +	u32 is_dmabuf : 1;
>  	struct work_struct	work;
>  	struct sg_table sg_head;
>  	int             nmap;
>  	unsigned int    sg_nents;
>  };
>  
> +struct ib_umem_dmabuf {
> +	struct ib_umem umem;
> +	struct dma_buf_attachment *attach;
> +	struct sg_table *sgt;
> +	void *device_context;
> +};
> +
> +static inline struct ib_umem_dmabuf *to_ib_umem_dmabuf(struct ib_umem *umem)
> +{
> +	return container_of(umem, struct ib_umem_dmabuf, umem);
> +}
> +
>  /* Returns the offset of the umem start relative to the first page. */
>  static inline int ib_umem_offset(struct ib_umem *umem)
>  {
> @@ -79,6 +94,12 @@ int ib_umem_copy_from(void *dst, struct ib_umem *umem, size_t offset,
>  unsigned long ib_umem_find_best_pgsz(struct ib_umem *umem,
>  				     unsigned long pgsz_bitmap,
>  				     unsigned long virt);
> +struct ib_umem *ib_umem_dmabuf_get(struct ib_device *device,
> +				   unsigned long offset, size_t size,
> +				   int fd, int access,
> +				   const struct dma_buf_attach_ops *ops);
> +int ib_umem_dmabuf_map_pages(struct ib_umem_dmabuf *umem_dmabuf);
> +void ib_umem_dmabuf_unmap_pages(struct ib_umem_dmabuf *umem_dmabuf);
>  
>  #else /* CONFIG_INFINIBAND_USER_MEM */
>  
> @@ -101,7 +122,19 @@ static inline unsigned long ib_umem_find_best_pgsz(struct ib_umem *umem,
>  {
>  	return 0;
>  }
> +static inline struct ib_umem *ib_umem_dmabuf_get(struct ib_device *device,
> +						 unsigned long offset,
> +						 size_t size, int fd,
> +						 int access,
> +						 struct dma_buf_attach_ops *ops)
> +{
> +	return ERR_PTR(-EINVAL);
> +}
> +static inline int ib_umem_dmabuf_map_pages(struct ib_umem_dmabuf *umem_dmabuf)
> +{
> +	return -EINVAL;
> +}
> +static inline void ib_umem_dmabuf_unmap_pages(struct ib_umem_dmabuf *umem_dmabuf) { }
>  
>  #endif /* CONFIG_INFINIBAND_USER_MEM */
> -
>  #endif /* IB_UMEM_H */
> -- 
> 1.8.3.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch