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

["Xiong, Jianxin" <jianxin.xiong@intel.com>]

> -----Original Message-----
> From: Daniel Vetter <daniel@ffwll.ch>
> Sent: Friday, October 23, 2020 9:49 AM
> To: Xiong, Jianxin <jianxin.xiong@intel.com>
> Cc: linux-rdma@vger.kernel.org; dri-devel@lists.freedesktop.org; Leon Romanovsky <leon@kernel.org>; Jason Gunthorpe <jgg@ziepe.ca>;
> Doug Ledford <dledford@redhat.com>; Vetter, Daniel <daniel.vetter@intel.com>; Christian Koenig <christian.koenig@amd.com>
> Subject: Re: [PATCH v6 1/4] RDMA/umem: Support importing dma-buf as user memory region
> 
> 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
> 

This is also checked by dma_buf_dynamic_attach(), not in the common code, but
in the exporter's attach() method. For example, the attach method of 'amdgpu' calls p2pdma_distance_many and would disable p2p if dma_virt_ops is detected.

Here we could instead check the peer2peer flag from the returned 'attach' structure.
 
> > +
> > +	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
> >
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch