On 2021-05-02 4:44 p.m., John Hubbard wrote:

On 4/8/21 10:01 AM, Logan Gunthorpe wrote:

quoted

pci_p2pdma_map_type() will be needed by the dma-iommu map_sg
implementation because it will need to determine the mapping type
ahead of actually doing the mapping to create the actual iommu mapping.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
  drivers/pci/p2pdma.c       | 34 +++++++++++++++++++++++-----------
  include/linux/pci-p2pdma.h | 15 +++++++++++++++
  2 files changed, 38 insertions(+), 11 deletions(-)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index bcb1a6d6119d..38c93f57a941 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c

@@ -20,13 +20,6 @@
  #include <linux/seq_buf.h>
  #include <linux/xarray.h>
  
-enum pci_p2pdma_map_type {
-	PCI_P2PDMA_MAP_UNKNOWN = 0,
-	PCI_P2PDMA_MAP_NOT_SUPPORTED,
-	PCI_P2PDMA_MAP_BUS_ADDR,
-	PCI_P2PDMA_MAP_THRU_HOST_BRIDGE,
-};
-
  struct pci_p2pdma {
  	struct gen_pool *pool;
  	bool p2pmem_published;

@@ -822,13 +815,30 @@ void pci_p2pmem_publish(struct pci_dev *pdev, bool publish)
  }
  EXPORT_SYMBOL_GPL(pci_p2pmem_publish);
  
-static enum pci_p2pdma_map_type pci_p2pdma_map_type(struct dev_pagemap *pgmap,
-						    struct device *dev)
+/**
+ * pci_p2pdma_map_type - return the type of mapping that should be used for
+ *	a given device and pgmap
+ * @pgmap: the pagemap of a page to determine the mapping type for
+ * @dev: device that is mapping the page
+ * @dma_attrs: the attributes passed to the dma_map operation --
+ *	this is so they can be checked to ensure P2PDMA pages were not
+ *	introduced into an incorrect interface (like dma_map_sg). *
+ *
+ * Returns one of:
+ *	PCI_P2PDMA_MAP_NOT_SUPPORTED - The mapping should not be done
+ *	PCI_P2PDMA_MAP_BUS_ADDR - The mapping should use the PCI bus address
+ *	PCI_P2PDMA_MAP_THRU_HOST_BRIDGE - The mapping should be done directly
+ */
+enum pci_p2pdma_map_type pci_p2pdma_map_type(struct dev_pagemap *pgmap,
+		struct device *dev, unsigned long dma_attrs)
  {
  	struct pci_dev *provider = to_p2p_pgmap(pgmap)->provider;
  	enum pci_p2pdma_map_type ret;
  	struct pci_dev *client;
  
+	WARN_ONCE(!(dma_attrs & __DMA_ATTR_PCI_P2PDMA),
+		  "PCI P2PDMA pages were mapped with dma_map_sg!");

This really ought to also return -EINVAL, assuming that my review suggestions
about return types, in earlier patches, are acceptable.

That can't happen because, by convention, dma_map_sg() cannot return
-EINVAL. I think the best we can do is proceed normally and just warn
loudly.

Logan