Attempt to find the mapping type for P2PDMA pages on the first
DMA map attempt if it has not been done ahead of time.

Previously, the mapping type was expected to be calculated ahead of
time, but if pages are to come from userspace then there's no
way to ensure the path was checked ahead of time.

This change will calculate the mapping type if it hasn't pre-calculated
so it is no longer invalid to call pci_p2pdma_map_sg() before the mapping
type is calculated, so drop the WARN_ON when that is the case.

Signed-off-by: Logan Gunthorpe <>
Acked-by: Bjorn Helgaas <>
Reviewed-by: Chaitanya Kulkarni <>
 drivers/pci/p2pdma.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 462b429ad243..4e8bc457e29a 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -854,6 +854,7 @@ static enum pci_p2pdma_map_type pci_p2pdma_map_type(struct 
dev_pagemap *pgmap,
        struct pci_dev *provider = to_p2p_pgmap(pgmap)->provider;
        struct pci_dev *client;
        struct pci_p2pdma *p2pdma;
+       int dist;
        if (!provider->p2pdma)
                return PCI_P2PDMA_MAP_NOT_SUPPORTED;
@@ -870,6 +871,10 @@ static enum pci_p2pdma_map_type pci_p2pdma_map_type(struct 
dev_pagemap *pgmap,
                type = xa_to_value(xa_load(&p2pdma->map_types,
+       if (type == PCI_P2PDMA_MAP_UNKNOWN)
+               return calc_map_type_and_dist(provider, client, &dist, true);
        return type;
@@ -912,7 +917,7 @@ int pci_p2pdma_map_sg_attrs(struct device *dev, struct 
scatterlist *sg,
        case PCI_P2PDMA_MAP_BUS_ADDR:
                return __pci_p2pdma_map_sg(p2p_pgmap, dev, sg, nents);
-               WARN_ON_ONCE(1);
+               /* Mapping is not Supported */
                return 0;

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