On Thu, Apr 16, 2020 at 10:09:31AM -0700, Jianxin Xiong wrote:
> Dma-buf, a standard cross-driver buffer sharing mechanism, is chosen to
> be the basis of a non-proprietary approach for supporting RDMA to/from
> buffers allocated from device local memory (e.g. GPU VRAM).
Where can I read more about "is chosen to be the basis of a
non-proprietary approach" part of the sentence?
Especially HMM vs. dma-buf in this regard.
>
> Dma-buf is supported by mainstream GPU drivers. By using ioctl calls
> via the devices under /dev/dri/, user space applications can allocate
> and export GPU buffers as dma-buf objects with associated file
> descriptors.
>
> In order to use the exported GPU buffers for RDMA operations, the RDMA
> driver needs to be able to import dma-buf objects. This happens at the
> time of memory registration. A GPU buffer is registered as a special
> type of user space memory region with the dma-buf file descriptor as
> an extra parameter. The uverbs API needs to be extended to allow the
> extra parameter be passed from user space to kernel.
>
> Implements the common code for pinning and mapping dma-buf pages and
> adds config option for RDMA driver dma-buf support. The common code
> is utilized by the new uverbs commands introduced by follow-up patches.
>
> Signed-off-by: Jianxin Xiong <jianxin.xiong@xxxxxxxxx>
> Reviewed-by: Sean Hefty <sean.hefty@xxxxxxxxx>
> Acked-by: Michael J. Ruhl <michael.j.ruhl@xxxxxxxxx>
> ---
> drivers/infiniband/Kconfig | 10 ++++
> drivers/infiniband/core/Makefile | 1 +
> drivers/infiniband/core/umem.c | 3 +
> drivers/infiniband/core/umem_dmabuf.c | 100 ++++++++++++++++++++++++++++++++++
> include/rdma/ib_umem.h | 2 +
> include/rdma/ib_umem_dmabuf.h | 50 +++++++++++++++++
> 6 files changed, 166 insertions(+)
> create mode 100644 drivers/infiniband/core/umem_dmabuf.c
> create mode 100644 include/rdma/ib_umem_dmabuf.h
>
> diff --git a/drivers/infiniband/Kconfig b/drivers/infiniband/Kconfig
> index ade8638..1dcfc59 100644
> --- a/drivers/infiniband/Kconfig
> +++ b/drivers/infiniband/Kconfig
> @@ -63,6 +63,16 @@ config INFINIBAND_ON_DEMAND_PAGING
> memory regions without pinning their pages, fetching the
> pages on demand instead.
>
> +config INFINIBAND_DMABUF
There is no need to add extra config, it is not different from any
other verbs feature which is handled by some sort of mask.
> + bool "InfiniBand dma-buf support"
> + depends on INFINIBAND_USER_MEM
> + default n
> + help
> + Support for dma-buf based user memory.
> + This allows userspace processes register memory regions
> + backed by device memory exported as dma-buf, and thus
> + enables RDMA operations using device memory.
> +
> config INFINIBAND_ADDR_TRANS
> bool "RDMA/CM"
> depends on INFINIBAND
> diff --git a/drivers/infiniband/core/Makefile b/drivers/infiniband/core/Makefile
> index d1b14887..7981d0f 100644
> --- a/drivers/infiniband/core/Makefile
> +++ b/drivers/infiniband/core/Makefile
> @@ -39,3 +39,4 @@ ib_uverbs-y := uverbs_main.o uverbs_cmd.o uverbs_marshall.o \
> uverbs_std_types_async_fd.o
> ib_uverbs-$(CONFIG_INFINIBAND_USER_MEM) += umem.o
> ib_uverbs-$(CONFIG_INFINIBAND_ON_DEMAND_PAGING) += umem_odp.o
> +ib_uverbs-$(CONFIG_INFINIBAND_DMABUF) += umem_dmabuf.o
> diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
> index 82455a1..54b35df 100644
> --- a/drivers/infiniband/core/umem.c
> +++ b/drivers/infiniband/core/umem.c
> @@ -40,6 +40,7 @@
> #include <linux/slab.h>
> #include <linux/pagemap.h>
> #include <rdma/ib_umem_odp.h>
> +#include <rdma/ib_umem_dmabuf.h>
>
> #include "uverbs.h"
>
> @@ -317,6 +318,8 @@ 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..325d44f
> --- /dev/null
> +++ b/drivers/infiniband/core/umem_dmabuf.c
> @@ -0,0 +1,100 @@
> +// SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause)
> +/*
> + * Copyright (c) 2020 Intel Corporation. All rights reserved.
> + */
> +
> +#include <linux/mm.h>
> +#include <linux/sched/mm.h>
> +#include <linux/dma-mapping.h>
> +#include <rdma/ib_umem_dmabuf.h>
> +
> +#include "uverbs.h"
> +
> +struct ib_umem *ib_umem_dmabuf_get(struct ib_device *device,
> + unsigned long addr, size_t size,
> + int dmabuf_fd, int access)
> +{
> + struct ib_umem_dmabuf *umem_dmabuf;
> + struct sg_table *sgt;
> + enum dma_data_direction dir;
> + long ret;
> +
> + if (((addr + size) < addr) ||
> + PAGE_ALIGN(addr + size) < (addr + size))
> + return ERR_PTR(-EINVAL);
> +
> + if (!can_do_mlock())
> + return ERR_PTR(-EPERM);
> +
> + if (access & IB_ACCESS_ON_DEMAND)
> + return ERR_PTR(-EOPNOTSUPP);
Does dma-buf really need to prohibit ODP?
> +
> + umem_dmabuf = kzalloc(sizeof(*umem_dmabuf), GFP_KERNEL);
> + if (!umem_dmabuf)
> + return ERR_PTR(-ENOMEM);
> +
> + umem_dmabuf->umem.ibdev = device;
> + umem_dmabuf->umem.length = size;
> + umem_dmabuf->umem.address = addr;
> + umem_dmabuf->umem.writable = ib_access_writable(access);
> + umem_dmabuf->umem.is_dmabuf = 1;
> + umem_dmabuf->umem.owning_mm = current->mm;
> + mmgrab(umem_dmabuf->umem.owning_mm);
> +
> + umem_dmabuf->fd = dmabuf_fd;
> + umem_dmabuf->dmabuf = dma_buf_get(umem_dmabuf->fd);
> + if (IS_ERR(umem_dmabuf->dmabuf)) {
> + ret = PTR_ERR(umem_dmabuf->dmabuf);
> + goto out_free_umem;
> + }
> +
> + umem_dmabuf->attach = dma_buf_attach(umem_dmabuf->dmabuf,
> + device->dma_device);
> + if (IS_ERR(umem_dmabuf->attach)) {
> + ret = PTR_ERR(umem_dmabuf->attach);
> + goto out_release_dmabuf;
> + }
> +
> + dir = umem_dmabuf->umem.writable ? DMA_BIDIRECTIONAL : DMA_FROM_DEVICE;
> + sgt = dma_buf_map_attachment(umem_dmabuf->attach, dir);
> + if (IS_ERR(sgt)) {
> + ret = PTR_ERR(sgt);
> + goto out_detach_dmabuf;
> + }
> +
> + umem_dmabuf->sgt = sgt;
> + umem_dmabuf->umem.sg_head = *sgt;
> + umem_dmabuf->umem.nmap = sgt->nents;
> + return &umem_dmabuf->umem;
> +
> +out_detach_dmabuf:
> + dma_buf_detach(umem_dmabuf->dmabuf, umem_dmabuf->attach);
> +
> +out_release_dmabuf:
> + dma_buf_put(umem_dmabuf->dmabuf);
> +
> +out_free_umem:
> + mmdrop(umem_dmabuf->umem.owning_mm);
> + kfree(umem_dmabuf);
> + return ERR_PTR(ret);
> +}
> +EXPORT_SYMBOL(ib_umem_dmabuf_get);
> +
> +void ib_umem_dmabuf_release(struct ib_umem_dmabuf *umem_dmabuf)
> +{
> + enum dma_data_direction dir;
> +
> + dir = umem_dmabuf->umem.writable ? DMA_BIDIRECTIONAL : DMA_FROM_DEVICE;
> +
> + /*
> + * Only use the original sgt returned from dma_buf_map_attachment(),
> + * otherwise the scatterlist may be freed twice due to the map caching
> + * mechanism.
> + */
> + dma_buf_unmap_attachment(umem_dmabuf->attach, umem_dmabuf->sgt, dir);
> + dma_buf_detach(umem_dmabuf->dmabuf, umem_dmabuf->attach);
> + dma_buf_put(umem_dmabuf->dmabuf);
> + mmdrop(umem_dmabuf->umem.owning_mm);
> + kfree(umem_dmabuf);
> +}
> +EXPORT_SYMBOL(ib_umem_dmabuf_release);
> diff --git a/include/rdma/ib_umem.h b/include/rdma/ib_umem.h
> index e3518fd..026a3cf 100644
> --- a/include/rdma/ib_umem.h
> +++ b/include/rdma/ib_umem.h
> @@ -40,6 +40,7 @@
>
> struct ib_ucontext;
> struct ib_umem_odp;
> +struct ib_umem_dmabuf;
>
> struct ib_umem {
> struct ib_device *ibdev;
> @@ -48,6 +49,7 @@ 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;
> diff --git a/include/rdma/ib_umem_dmabuf.h b/include/rdma/ib_umem_dmabuf.h
> new file mode 100644
> index 0000000..e82b205
> --- /dev/null
> +++ b/include/rdma/ib_umem_dmabuf.h
> @@ -0,0 +1,50 @@
> +/* SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause) */
> +/*
> + * Copyright (c) 2020 Intel Corporation. All rights reserved.
> + */
> +
> +#ifndef IB_UMEM_DMABUF_H
> +#define IB_UMEM_DMABUF_H
> +
> +#include <linux/dma-buf.h>
> +#include <rdma/ib_umem.h>
> +#include <rdma/ib_verbs.h>
> +
> +struct ib_umem_dmabuf {
> + struct ib_umem umem;
> + int fd;
> + struct dma_buf *dmabuf;
> + struct dma_buf_attachment *attach;
> + struct sg_table *sgt;
> +};
> +
> +static inline struct ib_umem_dmabuf *to_ib_umem_dmabuf(struct ib_umem *umem)
> +{
> + return container_of(umem, struct ib_umem_dmabuf, umem);
> +}
> +
> +#ifdef CONFIG_INFINIBAND_DMABUF
> +
> +struct ib_umem *ib_umem_dmabuf_get(struct ib_device *device,
> + unsigned long addr, size_t size,
> + int dmabuf_fd, int access);
> +
> +void ib_umem_dmabuf_release(struct ib_umem_dmabuf *umem_dmabuf);
> +
> +#else /* CONFIG_INFINIBAND_DMABUF */
> +
> +static inline struct ib_umem *ib_umem_dmabuf_get(struct ib_device *device,
> + unsigned long addr,
> + size_t size, int dmabuf_fd,
> + int access)
> +{
> + return ERR_PTR(-EINVAL);
> +}
> +
> +static inline void ib_umem_dmabuf_release(struct ib_umem_dmabuf *umem_dmabuf)
> +{
> +}
> +
> +#endif /* CONFIG_INFINIBAND_DMABUF */
> +
> +#endif /* IB_UMEM_DMABUF_H */
> --
> 1.8.3.1
>
