[PATCH v6 09/16] dma-mapping: implement DMA_ATTR_MMIO for dma_(un)map_page_attrs()

Leon Romanovsky
2025-09-09T13:29:02Z

Make dma_map_page_attrs() and dma_map_page_attrs() respect
DMA_ATTR_MMIO.

DMA_ATR_MMIO makes the functions behave the same as
dma_(un)map_resource():
- No swiotlb is possible
- Legacy dma_ops arches use ops->map_resource()
- No kmsan
- No arch_dma_map_phys_direct()

The prior patches have made the internal functions called here
support DMA_ATTR_MMIO.

This is also preparation for turning dma_map_resource() into an inline
calling dma_map_phys(DMA_ATTR_MMIO) to consolidate the flows.

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
kernel/dma/mapping.c | 26 +++++++++++++++++++++-----
1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index e47bcf7cc43d7..95eab531e2273 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -158,6 +158,7 @@ dma_addr_t dma_map_page_attrs(struct device *dev, struct page *page,
{
const struct dma_map_ops *ops = get_dma_ops(dev);
phys_addr_t phys = page_to_phys(page) + offset;
+ bool is_mmio = attrs & DMA_ATTR_MMIO;
dma_addr_t addr;

BUG_ON(!valid_dma_direction(dir));
@@ -166,14 +167,25 @@ dma_addr_t dma_map_page_attrs(struct device *dev, struct page *page,
return DMA_MAPPING_ERROR;

if (dma_map_direct(dev, ops) ||
- arch_dma_map_phys_direct(dev, phys + size))
+ (!is_mmio && arch_dma_map_phys_direct(dev, phys + size)))
addr = dma_direct_map_phys(dev, phys, size, dir, attrs);
else if (use_dma_iommu(dev))
addr = iommu_dma_map_phys(dev, phys, size, dir, attrs);
- else
+ else if (is_mmio) {
+ if (!ops->map_resource)
+ return DMA_MAPPING_ERROR;
+
+ addr = ops->map_resource(dev, phys, size, dir, attrs);
+ } else {
+ /*
+ * The dma_ops API contract for ops->map_page() requires
+ * kmappable memory, while ops->map_resource() does not.
+ */
addr = ops->map_page(dev, page, offset, size, dir, attrs);
+ }

- kmsan_handle_dma(phys, size, dir);
+ if (!is_mmio)
+ kmsan_handle_dma(phys, size, dir);
trace_dma_map_phys(dev, phys, addr, size, dir, attrs);
debug_dma_map_phys(dev, phys, size, dir, addr, attrs);

@@ -185,14 +197,18 @@ void dma_unmap_page_attrs(struct device *dev, dma_addr_t addr, size_t size,
enum dma_data_direction dir, unsigned long attrs)
{
const struct dma_map_ops *ops = get_dma_ops(dev);
+ bool is_mmio = attrs & DMA_ATTR_MMIO;

BUG_ON(!valid_dma_direction(dir));
if (dma_map_direct(dev, ops) ||
- arch_dma_unmap_phys_direct(dev, addr + size))
+ (!is_mmio && arch_dma_unmap_phys_direct(dev, addr + size)))
dma_direct_unmap_phys(dev, addr, size, dir, attrs);
else if (use_dma_iommu(dev))
iommu_dma_unmap_phys(dev, addr, size, dir, attrs);
- else
+ else if (is_mmio) {
+ if (ops->unmap_resource)
+ ops->unmap_resource(dev, addr, size, dir, attrs);
+ } else
ops->unmap_page(dev, addr, size, dir, attrs);
trace_dma_unmap_phys(dev, addr, size, dir, attrs);
debug_dma_unmap_phys(dev, addr, size, dir);
--
2.51.0