[PATCH v6 12/16] mm/hmm: migrate to physical address-based DMA mapping API

Leon Romanovsky
2025-09-09T13:29:17Z

Convert HMM DMA operations from the legacy page-based API to the new
physical address-based dma_map_phys() and dma_unmap_phys() functions.
This demonstrates the preferred approach for new code that should use
physical addresses directly rather than page+offset parameters.

The change replaces dma_map_page() and dma_unmap_page() calls with
dma_map_phys() and dma_unmap_phys() respectively, using the physical
address that was already available in the code. This eliminates the
redundant page-to-physical address conversion and aligns with the
DMA subsystem's move toward physical address-centric interfaces.

This serves as an example of how new code should be written to leverage
the more efficient physical address API, which provides cleaner interfaces
for drivers that already have access to physical addresses.

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
mm/hmm.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/hmm.c b/mm/hmm.c
index d545e24949949..015ab243f0813 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -775,8 +775,8 @@ dma_addr_t hmm_dma_map_pfn(struct device *dev, struct hmm_dma_map *map,
if (WARN_ON_ONCE(dma_need_unmap(dev) && !dma_addrs))
goto error;

- dma_addr = dma_map_page(dev, page, 0, map->dma_entry_size,
- DMA_BIDIRECTIONAL);
+ dma_addr = dma_map_phys(dev, paddr, map->dma_entry_size,
+ DMA_BIDIRECTIONAL, 0);
if (dma_mapping_error(dev, dma_addr))
goto error;

@@ -819,8 +819,8 @@ bool hmm_dma_unmap_pfn(struct device *dev, struct hmm_dma_map *map, size_t idx)
dma_iova_unlink(dev, state, idx * map->dma_entry_size,
map->dma_entry_size, DMA_BIDIRECTIONAL, attrs);
} else if (dma_need_unmap(dev))
- dma_unmap_page(dev, dma_addrs[idx], map->dma_entry_size,
- DMA_BIDIRECTIONAL);
+ dma_unmap_phys(dev, dma_addrs[idx], map->dma_entry_size,
+ DMA_BIDIRECTIONAL, 0);

pfns[idx] &=
~(HMM_PFN_DMA_MAPPED | HMM_PFN_P2PDMA | HMM_PFN_P2PDMA_BUS);
--
2.51.0