[PATCH v6 13/16] mm/hmm: properly take MMIO path

Leon Romanovsky
2025-09-09T13:29:05Z

In case peer-to-peer transaction traverses through host bridge,
the IOMMU needs to have IOMMU_MMIO flag, together with skip of
CPU sync.

The latter was handled by provided DMA_ATTR_SKIP_CPU_SYNC flag,
but IOMMU flag was missed, due to assumption that such memory
can be treated as regular one.

Reuse newly introduced DMA attribute to properly take MMIO path.

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
mm/hmm.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/mm/hmm.c b/mm/hmm.c
index 015ab243f0813..6556c0e074ba8 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -746,7 +746,7 @@ dma_addr_t hmm_dma_map_pfn(struct device *dev, struct hmm_dma_map *map,
case PCI_P2PDMA_MAP_NONE:
break;
case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
- attrs |= DMA_ATTR_SKIP_CPU_SYNC;
+ attrs |= DMA_ATTR_MMIO;
pfns[idx] |= HMM_PFN_P2PDMA;
break;
case PCI_P2PDMA_MAP_BUS_ADDR:
@@ -776,7 +776,7 @@ dma_addr_t hmm_dma_map_pfn(struct device *dev, struct hmm_dma_map *map,
goto error;

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

@@ -811,16 +811,17 @@ bool hmm_dma_unmap_pfn(struct device *dev, struct hmm_dma_map *map, size_t idx)
if ((pfns[idx] & valid_dma) != valid_dma)
return false;

+ if (pfns[idx] & HMM_PFN_P2PDMA)
+ attrs |= DMA_ATTR_MMIO;
+
if (pfns[idx] & HMM_PFN_P2PDMA_BUS)
; /* no need to unmap bus address P2P mappings */
- else if (dma_use_iova(state)) {
- if (pfns[idx] & HMM_PFN_P2PDMA)
- attrs |= DMA_ATTR_SKIP_CPU_SYNC;
+ else if (dma_use_iova(state))
dma_iova_unlink(dev, state, idx * map->dma_entry_size,
map->dma_entry_size, DMA_BIDIRECTIONAL, attrs);
- } else if (dma_need_unmap(dev))
+ else if (dma_need_unmap(dev))
dma_unmap_phys(dev, dma_addrs[idx], map->dma_entry_size,
- DMA_BIDIRECTIONAL, 0);
+ DMA_BIDIRECTIONAL, attrs);

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