2021-11-17 21:54:45

by Logan Gunthorpe

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

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 <[email protected]>
Acked-by: Bjorn Helgaas <[email protected]>
---
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)
return PCI_P2PDMA_MAP_NOT_SUPPORTED;
@@ -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,
map_types_idx(client)));
rcu_read_unlock();
+
+ 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,
case PCI_P2PDMA_MAP_BUS_ADDR:
return __pci_p2pdma_map_sg(p2p_pgmap, dev, sg, nents);
default:
- WARN_ON_ONCE(1);
return 0;
}
}
--
2.30.2

2021-12-13 22:00:35

by Chaitanya Kulkarni

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

On 11/17/21 1:53 PM, Logan Gunthorpe wrote:
> 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 <[email protected]>
> Acked-by: Bjorn Helgaas <[email protected]>
> ---

Perhaps a comment would be nice in the default case in
pci_p2pdma_map_sg_attrs() where you have removed the WARN_ON_ONCE().

Either way, looks good.

Reviewed-by: Chaitanya Kulkarni <[email protected]>