Re: [PATCH v3 07/10] nvme-pci: implement dma_token backed requests

Maurizio Lombardi
2026-04-29T16:07:55Z

On Wed Apr 29, 2026 at 5:25 PM CEST, Pavel Begunkov 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 <kbusch@kernel.org>
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
> drivers/nvme/host/pci.c | 282 ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 282 insertions(+)
>
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index db5fc9bf6627..d2629853a972 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/io_dmabuf_token.h>
> +#include <linux/dma-resv.h>
>
> #include "trace.h"
> #include "nvme.h"
> @@ -393,6 +395,17 @@ struct nvme_queue {
> struct completion delete_done;
> };
>
> +struct nvme_dmabuf_token {
> + struct dma_buf_attachment *attach;
> +};
> +
> +struct nvme_dmabuf_map {
> + struct io_dmabuf_map base;
> + dma_addr_t *dma_list;
> + struct sg_table *sgt;
> + unsigned nr_entries;
> +};
> +
> /* bits for iod->flags */
> enum nvme_iod_flags {
> /* this command has been aborted by the timeout handler */
> @@ -854,6 +867,134 @@ static void nvme_free_descriptors(struct request *req)
> }
> }
>
> +static void nvme_dmabuf_map_sync(struct nvme_dev *nvme_dev, struct request *req,
> + bool for_cpu)
> +{
> + int length = blk_rq_payload_bytes(req);
> + struct device *dev = nvme_dev->dev;
> + enum dma_data_direction dma_dir;
> + struct bio *bio = req->bio;
> + struct nvme_dmabuf_map *map;
> + dma_addr_t *dma_list;
> + int offset, map_idx;
> +
> + dma_dir = rq_data_dir(req) == READ ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
> + map = container_of(bio->dmabuf_map, struct nvme_dmabuf_map, base);
> + dma_list = map->dma_list;
> +
> + offset = bio->bi_iter.bi_bvec_done;
> + map_idx = offset / NVME_CTRL_PAGE_SIZE;
> + length += offset & (NVME_CTRL_PAGE_SIZE - 1);
> +
> + while (length > 0) {
> + u64 dma_addr = dma_list[map_idx++];
> +
> + if (for_cpu)
> + __dma_sync_single_for_cpu(dev, dma_addr,
> + NVME_CTRL_PAGE_SIZE, dma_dir);
> + else
> + __dma_sync_single_for_device(dev, dma_addr,
> + 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(dev, req, true);
> +
> + 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);
> + int length = blk_rq_payload_bytes(req);
> + u64 dma_addr, prp1_dma, prp2_dma;
> + struct bio *bio = req->bio;
> + struct nvme_dmabuf_map *map;
> + dma_addr_t *dma_list;
> + dma_addr_t prp_dma;
> + __le64 *prp_list;
> + int i, map_idx;
> + int offset;
> +
> + nvme_dmabuf_map_sync(nvmeq->dev, req, false);
> +
> + map = container_of(bio->dmabuf_map, struct nvme_dmabuf_map, base);
> + dma_list = map->dma_list;
> +
> + offset = bio->bi_iter.bi_bvec_done;
> + map_idx = offset / NVME_CTRL_PAGE_SIZE;
> + offset &= (NVME_CTRL_PAGE_SIZE - 1);
> + prp1_dma = dma_list[map_idx++] + offset;
> +
> + length -= (NVME_CTRL_PAGE_SIZE - offset);
> + 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);
> + 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 inline bool nvme_rq_is_dmabuf_attached(struct request *req)
> +{
> + if (!IS_ENABLED(CONFIG_DMABUF_TOKEN))
> + return false;
> + return req->bio && bio_flagged(req->bio, BIO_DMABUF_MAP);
> +}
> +
> static void nvme_free_prps(struct request *req, unsigned int attrs)
> {
> struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
> @@ -932,6 +1073,11 @@ static void nvme_unmap_data(struct request *req)
> struct device *dma_dev = nvmeq->dev->dev;
> unsigned int attrs = 0;
>
> + if (nvme_rq_is_dmabuf_attached(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));
> @@ -1222,6 +1368,9 @@ static blk_status_t nvme_map_data(struct request *req)
> struct blk_dma_iter iter;
> blk_status_t ret;
>
> + if (nvme_rq_is_dmabuf_attached(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.
> @@ -2238,6 +2387,134 @@ static int nvme_create_queue(struct nvme_queue *nvmeq, int qid, bool polled)
> return result;
> }
>
> +#ifdef CONFIG_DMABUF_TOKEN
> +static void nvme_dmabuf_invalidate_mappings(struct dma_buf_attachment *attach)
> +{
> + struct io_dmabuf_token *token = attach->importer_priv;
> +
> + io_dmabuf_token_invalidate_mappings(token);
> +}
> +
> +const struct dma_buf_attach_ops nvme_dmabuf_importer_ops = {
> + .invalidate_mappings = nvme_dmabuf_invalidate_mappings,
> + .allow_peer2peer = true,
> +};
> +
> +static struct io_dmabuf_map *nvme_dmabuf_token_map(struct io_dmabuf_token *token)
> +{
> + struct nvme_dmabuf_token *data = token->dev_priv;
> + struct dma_buf_attachment *attach = data->attach;
> + dma_addr_t *dma_list = NULL;
> + unsigned long tmp, i = 0;
> + struct nvme_dmabuf_map *map;
> + struct scatterlist *sg;
> + struct sg_table *sgt;
> + unsigned nr_entries;
> + int ret;
> +
> + dma_resv_assert_held(token->dmabuf->resv);
> +
> + map = kmalloc(sizeof(*map), GFP_KERNEL);
> + if (!map)
> + return ERR_PTR(-ENOMEM);
> +
> + nr_entries = token->dmabuf->size / NVME_CTRL_PAGE_SIZE;
> + dma_list = kmalloc_array(nr_entries, sizeof(dma_list[0]), GFP_KERNEL);
> + if (!dma_list) {
> + ret = -ENOMEM;
> + goto err;
> + }
> +
> + sgt = dma_buf_map_attachment(attach, token->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) {
> + dma_list[i++] = dma_addr;
> + dma_addr += NVME_CTRL_PAGE_SIZE;
> + sg_len -= NVME_CTRL_PAGE_SIZE;
> + }
> + }
> +
> + ret = io_dmabuf_init_map(token, &map->base);
> + if (ret)
> + goto err;
> + map->nr_entries = nr_entries;
> + map->dma_list = dma_list;
> + map->sgt = sgt;
> + return &map->base;
> +err:
> + if (sgt)
> + dma_buf_unmap_attachment(attach, sgt, token->dir);
> + kfree(map);
> + kfree(dma_list);
> + return ERR_PTR(ret);
> +}
> +
> +static void nvme_dmabuf_token_unmap(struct io_dmabuf_token *token,
> + struct io_dmabuf_map *map_base)
> +{
> + struct nvme_dmabuf_token *data = token->dev_priv;
> + struct nvme_dmabuf_map *map = container_of(map_base,
> + struct nvme_dmabuf_map, base);
> +
> + dma_resv_assert_held(token->dmabuf->resv);
> +
> + dma_buf_unmap_attachment(data->attach, map->sgt, token->dir);
> + kfree(map->dma_list);
> +}
> +
> +static void nvme_dmabuf_token_release(struct io_dmabuf_token *token)
> +{
> + struct nvme_dmabuf_token *data = token->dev_priv;
> +
> + dma_buf_detach(token->dmabuf, data->attach);
> + kfree(data);
> +}
> +
> +const struct io_dmabuf_token_dev_ops nvme_dma_token_ops = {
> + .map = nvme_dmabuf_token_map,
> + .unmap = nvme_dmabuf_token_unmap,
> + .release = nvme_dmabuf_token_release,
> +};
> +
> +static int nvme_create_dmabuf_token(struct request_queue *q,
> + struct io_dmabuf_token *token)
> +{
> + struct nvme_dmabuf_token *data;
> + struct dma_buf_attachment *attach;
> + struct nvme_ns *ns = q->queuedata;
> + struct nvme_dev *dev = to_nvme_dev(ns->ctrl);
> + struct dma_buf *dmabuf = token->dmabuf;
> +
> + data = kzalloc(sizeof(data), GFP_KERNEL);
> + if (!data)
> + return -ENOMEM;

Shouldn't this be kzalloc(sizeof(*data)...) ?

Also, checkpatch generates a warning because kzalloc_obj() should be
preferred for this kind of memory allocations over kzalloc().

> +
> + token->dev_priv = data;
> + token->dev_ops = &nvme_dma_token_ops;
> +
> + attach = dma_buf_dynamic_attach(dmabuf, dev->dev,
> + &nvme_dmabuf_importer_ops, token);
> + if (IS_ERR(attach))
> + return PTR_ERR(attach);

Supposing dma_buf_dynamic_attach() returns an error, won't the 'data'
pointer be leaked?

Maurizio