On Tue, Jul 28, 2026 at 2:35 PM Pavel Begunkov <[email protected]> wrote:
>
> Enable BIO_DMABUF_MAP backed requests. It creates a prp list for the
> dmabuf when it's mapped, which is then used to initialise requests.
>
> Suggested-by: Keith Busch <[email protected]>
> Signed-off-by: Pavel Begunkov <[email protected]>
> ---
> drivers/nvme/host/core.c | 12 ++
> drivers/nvme/host/nvme.h | 2 +
> drivers/nvme/host/pci.c | 259 +++++++++++++++++++++++++++++++++++++++
> 3 files changed, 273 insertions(+)
>
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 453c1f0b2dd0..ce66a1843bec 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -2676,6 +2676,17 @@ static int nvme_report_zones(struct gendisk *disk,
> sector_t sector,
> #define nvme_report_zones NULL
> #endif /* CONFIG_BLK_DEV_ZONED */
>
> +static int nvme_init_dma_buf_io_ctx(struct block_device *bdev,
> + struct dma_buf_io_ctx *ctx)
> +{
> + struct nvme_ns *ns = bdev->bd_disk->private_data;
> + struct nvme_ctrl *ctrl = ns->ctrl;
> +
> + if (!ctrl->ops->init_dma_buf_io_ctx)
> + return -EINVAL;
> + return ctrl->ops->init_dma_buf_io_ctx(ctrl, ctx);
> +}
> +
> const struct block_device_operations nvme_bdev_ops = {
> .owner = THIS_MODULE,
> .ioctl = nvme_ioctl,
> @@ -2686,6 +2697,7 @@ const struct block_device_operations nvme_bdev_ops = {
> .get_unique_id = nvme_get_unique_id,
> .report_zones = nvme_report_zones,
> .pr_ops = &nvme_pr_ops,
> + .init_dma_buf_io_ctx = nvme_init_dma_buf_io_ctx,
> };
>
> static int nvme_wait_ready(struct nvme_ctrl *ctrl, u32 mask, u32 val,
> diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
> index 824651cc898d..034c31af8fec 100644
> --- a/drivers/nvme/host/nvme.h
> +++ b/drivers/nvme/host/nvme.h
> @@ -652,6 +652,8 @@ struct nvme_ctrl_ops {
> int (*get_address)(struct nvme_ctrl *ctrl, char *buf, int size);
> void (*print_device_info)(struct nvme_ctrl *ctrl);
> bool (*supports_pci_p2pdma)(struct nvme_ctrl *ctrl);
> + int (*init_dma_buf_io_ctx)(struct nvme_ctrl *ctrl,
> + struct dma_buf_io_ctx *ctx);
> unsigned long (*get_virt_boundary)(struct nvme_ctrl *ctrl, bool
> is_admin);
> };
>
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index 69932d640b53..f1b67c191892 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -27,6 +27,8 @@
> #include <linux/io-64-nonatomic-lo-hi.h>
> #include <linux/io-64-nonatomic-hi-lo.h>
> #include <linux/sed-opal.h>
> +#include <linux/dma-buf-io.h>
> +#include <linux/dma-resv.h>
>
> #include "trace.h"
> #include "nvme.h"
> @@ -393,6 +395,13 @@ struct nvme_queue {
> struct completion delete_done;
> };
>
> +struct nvme_dmabuf_map {
> + struct dma_buf_io_map base;
> + struct sg_table *sgt;
> + unsigned nr_entries;
> + dma_addr_t dma_list[];
> +};
> +
> /* bits for iod->flags */
> enum nvme_iod_flags {
> /* this command has been aborted by the timeout handler */
> @@ -859,6 +868,138 @@ static void nvme_free_descriptors(struct request *req)
> }
> }
>
> +static inline struct nvme_dmabuf_map *
> +to_nvme_dmabuf_map(struct dma_buf_io_map *map)
> +{
> + return container_of(map, struct nvme_dmabuf_map, base);
> +}
> +
> +static void nvme_dmabuf_map_sync_for_cpu(struct nvme_dev *nvme_dev,
> + struct request *req)
> +{
> + struct device *dev = nvme_dev->dev;
> + enum dma_data_direction dma_dir;
> + struct bio *bio = req->bio;
> + struct nvme_dmabuf_map *map = to_nvme_dmabuf_map(bio->bi_dmabuf_map);
> + dma_addr_t *dma_list = map->dma_list;
> + unsigned offset = bio->bi_iter.bi_offset;
> + unsigned map_idx = offset / NVME_CTRL_PAGE_SIZE;
> + int length = blk_rq_payload_bytes(req) +
> + (offset & (NVME_CTRL_PAGE_SIZE - 1));
> +
> + dma_dir = rq_data_dir(req) == READ ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
> +
> + while (length > 0) {
> + dma_sync_single_for_cpu(dev, dma_list[map_idx++],
> + NVME_CTRL_PAGE_SIZE, dma_dir);
> + length -= NVME_CTRL_PAGE_SIZE;
> + }
> +}
> +
> +static void nvme_dmabuf_map_sync_for_device(struct nvme_dev *nvme_dev,
> + struct request *req)
> +{
> + struct device *dev = nvme_dev->dev;
> + enum dma_data_direction dma_dir;
> + struct bio *bio = req->bio;
> + struct nvme_dmabuf_map *map = to_nvme_dmabuf_map(bio->bi_dmabuf_map);
> + dma_addr_t *dma_list = map->dma_list;
> + unsigned offset = bio->bi_iter.bi_offset;
> + unsigned map_idx = offset / NVME_CTRL_PAGE_SIZE;
> + int length = blk_rq_payload_bytes(req) +
> + (offset & (NVME_CTRL_PAGE_SIZE - 1));
> +
> + dma_dir = rq_data_dir(req) == READ ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
> +
> + while (length > 0) {
> + dma_sync_single_for_device(dev, dma_list[map_idx++],
> + NVME_CTRL_PAGE_SIZE, dma_dir);
> + length -= NVME_CTRL_PAGE_SIZE;
> + }
> +}
> +
> +static void nvme_rq_clean_dmabuf_map(struct nvme_dev *dev,
> + struct request *req)
> +{
> + struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
> +
> + nvme_dmabuf_map_sync_for_cpu(dev, req);
> +
> + if (!(iod->flags & IOD_SINGLE_SEGMENT))
> + nvme_free_descriptors(req);
> +}
> +
> +static blk_status_t nvme_rq_setup_dmabuf_map(struct request *req,
> + struct nvme_queue *nvmeq)
> +{
> + struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
> + struct bio *bio = req->bio;
> + struct nvme_dmabuf_map *map = to_nvme_dmabuf_map(bio->bi_dmabuf_map);
> + unsigned bvec_done = bio->bi_iter.bi_offset;
> + unsigned map_idx = bvec_done / NVME_CTRL_PAGE_SIZE;
> + unsigned offset = bvec_done & (NVME_CTRL_PAGE_SIZE - 1);
> + int length = blk_rq_payload_bytes(req) - (NVME_CTRL_PAGE_SIZE -
> offset);
> + dma_addr_t *dma_list = map->dma_list;
> + u64 prp1_dma = dma_list[map_idx++] + offset;
> + u64 dma_addr, prp2_dma;
> + dma_addr_t prp_dma;
> + __le64 *prp_list;
> + unsigned i;
> +
> + nvme_dmabuf_map_sync_for_device(nvmeq->dev, req);
> +
> + if (length <= 0) {
> + prp2_dma = 0;
> + goto done;
> + }
> +
> + if (length <= NVME_CTRL_PAGE_SIZE) {
> + prp2_dma = dma_list[map_idx];
> + goto done;
> + }
> +
> + if (DIV_ROUND_UP(length, NVME_CTRL_PAGE_SIZE) <=
> + NVME_SMALL_POOL_SIZE / sizeof(__le64))
> + iod->flags |= IOD_SMALL_DESCRIPTOR;
> +
> + prp_list = dma_pool_alloc(nvme_dma_pool(nvmeq, iod), GFP_ATOMIC,
> + &prp_dma);
I wonder if it's possible to perform the PRP list page allocations and
initialization in nvme_dma_buf_io_map() instead of the I/O path. The
NVMe dma_pools are per-NUMA-node linked lists protected by spinlocks,
making them significant CPU hotspots. If the dmabuf registration set
up a contiguous DMA-coherent list of PRP entries for the pages of the
registered buffer, any command using the dmabuf and requiring at most
1 PRP list page (i.e. length <= 2 MB) could just set its PRP list
pointer to an offset into the dmabuf's PRP list.
Best,
Caleb
> + if (!prp_list)
> + return BLK_STS_RESOURCE;
> +
> + iod->descriptors[iod->nr_descriptors++] = prp_list;
> + prp2_dma = prp_dma;
> + i = 0;
> + for (;;) {
> + if (i == NVME_CTRL_PAGE_SIZE >> 3) {
> + __le64 *old_prp_list = prp_list;
> +
> + prp_list =
> dma_pool_alloc(nvmeq->descriptor_pools.large,
> + GFP_ATOMIC, &prp_dma);
> + if (!prp_list)
> + goto free_prps;
> + iod->descriptors[iod->nr_descriptors++] = prp_list;
> + prp_list[0] = old_prp_list[i - 1];
> + old_prp_list[i - 1] = cpu_to_le64(prp_dma);
> + i = 1;
> + }
> +
> + dma_addr = dma_list[map_idx++];
> + prp_list[i++] = cpu_to_le64(dma_addr);
> +
> + length -= NVME_CTRL_PAGE_SIZE;
> + if (length <= 0)
> + break;
> + }
> +done:
> + iod->cmd.common.dptr.prp1 = cpu_to_le64(prp1_dma);
> + iod->cmd.common.dptr.prp2 = cpu_to_le64(prp2_dma);
> + return BLK_STS_OK;
> +free_prps:
> + nvme_free_descriptors(req);
> + return BLK_STS_RESOURCE;
> +}
> +
> static void nvme_free_prps(struct request *req, unsigned int attrs)
> {
> struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
> @@ -937,6 +1078,11 @@ static void nvme_unmap_data(struct request *req)
> struct device *dma_dev = nvmeq->dev->dev;
> unsigned int attrs = 0;
>
> + if (blk_mq_rq_is_dmabuf(req)) {
> + nvme_rq_clean_dmabuf_map(nvmeq->dev, req);
> + return;
> + }
> +
> if (iod->flags & IOD_SINGLE_SEGMENT) {
> static_assert(offsetof(union nvme_data_ptr, prp1) ==
> offsetof(union nvme_data_ptr, sgl.addr));
> @@ -1251,6 +1397,9 @@ static blk_status_t nvme_map_data(struct request *req)
> struct blk_dma_iter iter;
> blk_status_t ret;
>
> + if (blk_mq_rq_is_dmabuf(req))
> + return nvme_rq_setup_dmabuf_map(req, nvmeq);
> +
> /*
> * Try to skip the DMA iterator for single segment requests, as that
> * significantly improves performances for small I/O sizes.
> @@ -2269,6 +2418,112 @@ static int nvme_create_queue(struct nvme_queue
> *nvmeq, int qid, bool polled)
> return result;
> }
>
> +#if defined(CONFIG_DMA_SHARED_BUFFER)
> +static void nvme_dmabuf_invalidate_mappings(struct dma_buf_attachment
> *attach)
> +{
> + struct dma_buf_io_ctx *ctx = attach->importer_priv;
> +
> + dma_buf_io_invalidate_mappings(ctx);
> +}
> +
> +const struct dma_buf_attach_ops nvme_dmabuf_importer_ops = {
> + .invalidate_mappings = nvme_dmabuf_invalidate_mappings,
> + .allow_peer2peer = true,
> +};
> +
> +static struct dma_buf_io_map *nvme_dma_buf_io_map(struct dma_buf_io_ctx *ctx)
> +{
> + unsigned nr_entries = ctx->dmabuf->size / NVME_CTRL_PAGE_SIZE;
> + struct dma_buf_attachment *attach = ctx->dev_priv;
> + unsigned long tmp, i = 0;
> + struct nvme_dmabuf_map *map;
> + struct scatterlist *sg;
> + struct sg_table *sgt;
> + int ret;
> +
> + dma_resv_assert_held(ctx->dmabuf->resv);
> +
> + map = kmalloc_flex(*map, dma_list, nr_entries);
> + if (!map)
> + return ERR_PTR(-ENOMEM);
> +
> + sgt = dma_buf_map_attachment(attach, ctx->dir);
> + if (IS_ERR(sgt)) {
> + ret = PTR_ERR(sgt);
> + sgt = NULL;
> + goto err;
> + }
> +
> + for_each_sgtable_dma_sg(sgt, sg, tmp) {
> + dma_addr_t dma_addr = sg_dma_address(sg);
> + unsigned long sg_len = sg_dma_len(sg);
> +
> + if (sg_len % NVME_CTRL_PAGE_SIZE) {
> + ret = -EINVAL;
> + goto err;
> + }
> +
> + while (sg_len) {
> + map->dma_list[i++] = dma_addr;
> + dma_addr += NVME_CTRL_PAGE_SIZE;
> + sg_len -= NVME_CTRL_PAGE_SIZE;
> + }
> + }
> +
> + ret = dma_buf_io_init_map(ctx, &map->base);
> + if (ret)
> + goto err;
> + map->nr_entries = nr_entries;
> + map->sgt = sgt;
> + return &map->base;
> +err:
> + if (sgt)
> + dma_buf_unmap_attachment(attach, sgt, ctx->dir);
> + kfree(map);
> + return ERR_PTR(ret);
> +}
> +
> +static void nvme_dma_buf_io_unmap(struct dma_buf_io_ctx *ctx,
> + struct dma_buf_io_map *map_base)
> +{
> + struct dma_buf_attachment *attach = ctx->dev_priv;
> + struct nvme_dmabuf_map *map = to_nvme_dmabuf_map(map_base);
> +
> + dma_resv_assert_held(ctx->dmabuf->resv);
> +
> + dma_buf_unmap_attachment(attach, map->sgt, ctx->dir);
> +}
> +
> +static void nvme_dma_buf_io_release(struct dma_buf_io_ctx *ctx)
> +{
> + struct dma_buf_attachment *attach = ctx->dev_priv;
> +
> + dma_buf_detach(ctx->dmabuf, attach);
> +}
> +
> +const struct dma_buf_io_ops nvme_dma_buf_io_ops = {
> + .map = nvme_dma_buf_io_map,
> + .unmap = nvme_dma_buf_io_unmap,
> + .release = nvme_dma_buf_io_release,
> +};
> +
> +static int nvme_pci_init_dma_buf_io_ctx(struct nvme_ctrl *ctrl,
> + struct dma_buf_io_ctx *ctx)
> +{
> + struct dma_buf_attachment *attach;
> + struct nvme_dev *dev = to_nvme_dev(ctrl);
> +
> + attach = dma_buf_dynamic_attach(ctx->dmabuf, dev->dev,
> + &nvme_dmabuf_importer_ops, ctx);
> + if (IS_ERR(attach))
> + return PTR_ERR(attach);
> +
> + ctx->dev_priv = attach;
> + ctx->dev_ops = &nvme_dma_buf_io_ops;
> + return 0;
> +}
> +#endif
> +
> static const struct blk_mq_ops nvme_mq_admin_ops = {
> .queue_rq = nvme_queue_rq,
> .complete = nvme_pci_complete_rq,
> @@ -3563,6 +3818,9 @@ static const struct nvme_ctrl_ops nvme_pci_ctrl_ops = {
> .print_device_info = nvme_pci_print_device_info,
> .supports_pci_p2pdma = nvme_pci_supports_pci_p2pdma,
> .get_virt_boundary = nvme_pci_get_virt_boundary,
> +#if defined(CONFIG_DMA_SHARED_BUFFER)
> + .init_dma_buf_io_ctx = nvme_pci_init_dma_buf_io_ctx,
> +#endif
> };
>
> static int nvme_dev_map(struct nvme_dev *dev)
> @@ -4327,5 +4585,6 @@ MODULE_AUTHOR("Matthew Wilcox <[email protected]>");
> MODULE_LICENSE("GPL");
> MODULE_VERSION("1.0");
> MODULE_DESCRIPTION("NVMe host PCIe transport driver");
> +MODULE_IMPORT_NS("DMA_BUF");
> module_init(nvme_init);
> module_exit(nvme_exit);
> --
> 2.54.0
>
>
