From: David Woodhouse <[email protected]>
The dma-buf phys-map dispatch used by iommufd's IOMMU_IOAS_MAP_FILE path
currently knows only about the VFIO PCI exporter (looked up via
symbol_get(vfio_pci_dma_buf_iommufd_map)). Widen the dispatch so
additional exporters can advertise the same well-known symbol name
convention and have their dma-bufs mapped without an explicit iommufd
dependency in each exporter's module.
For now the dispatch tries the sample guest_memfd provider's exporter
first, then falls back to VFIO PCI, both via symbol_get. This mirrors
the pattern the in-tree comment already flags:
"iommufd and vfio have a circular dependency. Future work for a
phys based private interconnect will remove this."
The eventual formal negotiated dma_buf_ops op that returns phys plus a
memory-type descriptor will subsume both of these lookups. The next
patch plumbs the memory type through iommufd; a follow-up will convert
the symbol lookups to the negotiated op.
Based on a proof-of-concept by Connor Williamson <[email protected]>
Signed-off-by: David Woodhouse (Kiro) <[email protected]>
---
drivers/iommu/iommufd/pages.c | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/drivers/iommu/iommufd/pages.c b/drivers/iommu/iommufd/pages.c
index 03c8379bbc34..2d4ea41460fd 100644
--- a/drivers/iommu/iommufd/pages.c
+++ b/drivers/iommu/iommufd/pages.c
@@ -1470,6 +1470,26 @@ sym_vfio_pci_dma_buf_iommufd_map(struct
dma_buf_attachment *attachment,
if (rc != -EOPNOTSUPP)
return rc;
+ /*
+ * Prototype: try the sample gmem provider's dma-buf exporter. This
+ * mirrors the vfio-pci private-interconnect hook, and (like it) is
+ * meant to be replaced by a formal negotiated exporter op returning
+ * phys for iommufd.
+ */
+ {
+ extern int gmem_provider_dma_buf_iommufd_map(
+ struct dma_buf_attachment *, struct phys_vec *);
+ typeof(&gmem_provider_dma_buf_iommufd_map) gfn;
+
+ gfn = symbol_get(gmem_provider_dma_buf_iommufd_map);
+ if (gfn) {
+ rc = gfn(attachment, phys);
+ symbol_put(gmem_provider_dma_buf_iommufd_map);
+ if (rc != -EOPNOTSUPP)
+ return rc;
+ }
+ }
+
if (!IS_ENABLED(CONFIG_VFIO_PCI_DMABUF))
return -EOPNOTSUPP;
--
2.54.0
