[PATCH v4 03/23] PCI/P2PDMA: Attempt to set map_type if it has not been set

From: Logan Gunthorpe
Date: Wed Nov 17 2021 - 16:54:44 EST

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 he case.

Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
drivers/pci/p2pdma.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 8d47cb7218d1..9a39c2c307ab 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -848,6 +848,7 @@ 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)
@@ -864,6 +865,10 @@ 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;

@@ -906,7 +911,6 @@ int pci_p2pdma_map_sg_attrs(struct device *dev, struct scatterlist *sg,
return __pci_p2pdma_map_sg(p2p_pgmap, dev, sg, nents);
return 0;