[PATCH 3/3] block-dma: properly take MMIO path

Leon Romanovsky
2025-10-17T05:32:22Z

From: Leon Romanovsky <leonro@nvidia.com>

Make sure that CPU is not synced and IOMMU is configured to take
MMIO path by providing newly introduced DMA_ATTR_MMIO attribute.

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
block/blk-mq-dma.c | 10 ++++++++--
include/linux/bio-integrity.h | 1 +
include/linux/blk-integrity.h | 3 ++-
include/linux/blk-mq-dma.h | 14 +++++++++++---
include/linux/blk_types.h | 2 ++
5 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/block/blk-mq-dma.c b/block/blk-mq-dma.c
index 4ba7b0323da4..e1f460da95d7 100644
--- a/block/blk-mq-dma.c
+++ b/block/blk-mq-dma.c
@@ -94,7 +94,7 @@ static bool blk_dma_map_direct(struct request *req, struct device *dma_dev,
struct blk_dma_iter *iter, struct phys_vec *vec)
{
iter->addr = dma_map_phys(dma_dev, vec->paddr, vec->len,
- rq_dma_dir(req), 0);
+ rq_dma_dir(req), iter->iter.attrs);
if (dma_mapping_error(dma_dev, iter->addr)) {
iter->status = BLK_STS_RESOURCE;
return false;
@@ -116,7 +116,7 @@ static bool blk_rq_dma_map_iova(struct request *req, struct device *dma_dev,

do {
error = dma_iova_link(dma_dev, state, vec->paddr, mapped,
- vec->len, dir, 0);
+ vec->len, dir, iter->iter.attrs);
if (error)
break;
mapped += vec->len;
@@ -184,6 +184,12 @@ static bool blk_dma_map_iter_start(struct request *req, struct device *dma_dev,
* P2P transfers through the host bridge are treated the
* same as non-P2P transfers below and during unmap.
*/
+ if (iter->iter.is_integrity)
+ bio_integrity(req->bio)->bip_flags |= BIP_MMIO;
+ else
+ req->cmd_flags |= REQ_MMIO;
+ iter->iter.attrs |= DMA_ATTR_MMIO;
+ fallthrough;
case PCI_P2PDMA_MAP_NONE:
break;
default:
diff --git a/include/linux/bio-integrity.h b/include/linux/bio-integrity.h
index 851254f36eb3..b77b2cfb7b0f 100644
--- a/include/linux/bio-integrity.h
+++ b/include/linux/bio-integrity.h
@@ -14,6 +14,7 @@ enum bip_flags {
BIP_CHECK_REFTAG = 1 << 6, /* reftag check */
BIP_CHECK_APPTAG = 1 << 7, /* apptag check */
BIP_P2P_DMA = 1 << 8, /* using P2P address */
+ BIP_MMIO = 1 << 9, /* contains MMIO memory */
};

struct bio_integrity_payload {
diff --git a/include/linux/blk-integrity.h b/include/linux/blk-integrity.h
index b659373788f6..34648d6c14d7 100644
--- a/include/linux/blk-integrity.h
+++ b/include/linux/blk-integrity.h
@@ -33,7 +33,8 @@ static inline bool blk_rq_integrity_dma_unmap(struct request *req,
size_t mapped_len)
{
return blk_dma_unmap(req, dma_dev, state, mapped_len,
- bio_integrity(req->bio)->bip_flags & BIP_P2P_DMA);
+ bio_integrity(req->bio)->bip_flags & BIP_P2P_DMA,
+ bio_integrity(req->bio)->bip_flags & BIP_MMIO);
}

int blk_rq_count_integrity_sg(struct request_queue *, struct bio *);
diff --git a/include/linux/blk-mq-dma.h b/include/linux/blk-mq-dma.h
index 51829958d872..916ca1deaf2c 100644
--- a/include/linux/blk-mq-dma.h
+++ b/include/linux/blk-mq-dma.h
@@ -10,6 +10,7 @@ struct blk_map_iter {
struct bio *bio;
struct bio_vec *bvecs;
bool is_integrity;
+ unsigned int attrs;
};

struct blk_dma_iter {
@@ -49,19 +50,25 @@ static inline bool blk_rq_dma_map_coalesce(struct dma_iova_state *state)
* @state: DMA IOVA state
* @mapped_len: number of bytes to unmap
* @is_p2p: true if mapped with PCI_P2PDMA_MAP_BUS_ADDR
+ * @is_mmio: true if mapped with PCI_P2PDMA_MAP_THRU_HOST_BRIDGE
*
* Returns %false if the callers need to manually unmap every DMA segment
* mapped using @iter or %true if no work is left to be done.
*/
static inline bool blk_dma_unmap(struct request *req, struct device *dma_dev,
- struct dma_iova_state *state, size_t mapped_len, bool is_p2p)
+ struct dma_iova_state *state, size_t mapped_len, bool is_p2p,
+ bool is_mmio)
{
if (is_p2p)
return true;

if (dma_use_iova(state)) {
+ unsigned int attrs = 0;
+
+ if (is_mmio)
+ attrs = DMA_ATTR_MMIO;
dma_iova_destroy(dma_dev, state, mapped_len, rq_dma_dir(req),
- 0);
+ attrs);
return true;
}

@@ -72,7 +79,8 @@ static inline bool blk_rq_dma_unmap(struct request *req, struct device *dma_dev,
struct dma_iova_state *state, size_t mapped_len)
{
return blk_dma_unmap(req, dma_dev, state, mapped_len,
- req->cmd_flags & REQ_P2PDMA);
+ req->cmd_flags & REQ_P2PDMA,
+ req->cmd_flags & REQ_MMIO);
}

#endif /* BLK_MQ_DMA_H */
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 8e8d1cc8b06c..9affa3b2d047 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -382,6 +382,7 @@ enum req_flag_bits {
__REQ_FS_PRIVATE, /* for file system (submitter) use */
__REQ_ATOMIC, /* for atomic write operations */
__REQ_P2PDMA, /* contains P2P DMA pages */
+ __REQ_MMIO, /* contains MMIO memory */
/*
* Command specific flags, keep last:
*/
@@ -415,6 +416,7 @@ enum req_flag_bits {
#define REQ_FS_PRIVATE (__force blk_opf_t)(1ULL << __REQ_FS_PRIVATE)
#define REQ_ATOMIC (__force blk_opf_t)(1ULL << __REQ_ATOMIC)
#define REQ_P2PDMA (__force blk_opf_t)(1ULL << __REQ_P2PDMA)
+#define REQ_MMIO (__force blk_opf_t)(1ULL << __REQ_MMIO)

#define REQ_NOUNMAP (__force blk_opf_t)(1ULL << __REQ_NOUNMAP)

--
2.51.0