[PATCH v8 05/13] dma-direct: support PCI P2PDMA pages in dma-direct map_sg

Logan Gunthorpe
2022-07-08T16:51:28Z

Add PCI P2PDMA support for dma_direct_map_sg() so that it can map
PCI P2PDMA pages directly without a hack in the callers. This allows
for heterogeneous SGLs that contain both P2PDMA and regular pages.

A P2PDMA page may have three possible outcomes when being mapped:
1) If the data path between the two devices doesn't go through the
root port, then it should be mapped with a PCI bus address
2) If the data path goes through the host bridge, it should be mapped
normally, as though it were a CPU physical address
3) It is not possible for the two devices to communicate and thus
the mapping operation should fail (and it will return -EREMOTEIO).

SGL segments that contain PCI bus addresses are marked with
sg_dma_mark_pci_p2pdma() and are ignored when unmapped.

P2PDMA mappings are also failed if swiotlb needs to be used on the
mapping.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
kernel/dma/direct.c | 43 +++++++++++++++++++++++++++++++++++++------
kernel/dma/direct.h | 8 +++++++-
2 files changed, 44 insertions(+), 7 deletions(-)

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 8d0b68a17042..63859a101ed8 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -453,29 +453,60 @@ void dma_direct_sync_sg_for_cpu(struct device *dev,
arch_sync_dma_for_cpu_all();
}

+/*
+ * Unmaps segments, except for ones marked as pci_p2pdma which do not
+ * require any further action as they contain a bus address.
+ */
void dma_direct_unmap_sg(struct device *dev, struct scatterlist *sgl,
int nents, enum dma_data_direction dir, unsigned long attrs)
{
struct scatterlist *sg;
int i;

- for_each_sg(sgl, sg, nents, i)
- dma_direct_unmap_page(dev, sg->dma_address, sg_dma_len(sg), dir,
- attrs);
+ for_each_sg(sgl, sg, nents, i) {
+ if (sg_is_dma_bus_address(sg))
+ sg_dma_unmark_bus_address(sg);
+ else
+ dma_direct_unmap_page(dev, sg->dma_address,
+ sg_dma_len(sg), dir, attrs);
+ }
}
#endif

int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
enum dma_data_direction dir, unsigned long attrs)
{
- int i;
+ struct pci_p2pdma_map_state p2pdma_state = {};
+ enum pci_p2pdma_map_type map;
struct scatterlist *sg;
+ int i, ret;

for_each_sg(sgl, sg, nents, i) {
+ if (is_pci_p2pdma_page(sg_page(sg))) {
+ map = pci_p2pdma_map_segment(&p2pdma_state, dev, sg);
+ switch (map) {
+ case PCI_P2PDMA_MAP_BUS_ADDR:
+ continue;
+ case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
+ /*
+ * Any P2P mapping that traverses the PCI
+ * host bridge must be mapped with CPU physical
+ * address and not PCI bus addresses. This is
+ * done with dma_direct_map_page() below.
+ */
+ break;
+ default:
+ ret = -EREMOTEIO;
+ goto out_unmap;
+ }
+ }
+
sg->dma_address = dma_direct_map_page(dev, sg_page(sg),
sg->offset, sg->length, dir, attrs);
- if (sg->dma_address == DMA_MAPPING_ERROR)
+ if (sg->dma_address == DMA_MAPPING_ERROR) {
+ ret = -EIO;
goto out_unmap;
+ }
sg_dma_len(sg) = sg->length;
}

@@ -483,7 +514,7 @@ int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents,

out_unmap:
dma_direct_unmap_sg(dev, sgl, i, dir, attrs | DMA_ATTR_SKIP_CPU_SYNC);
- return -EIO;
+ return ret;
}

dma_addr_t dma_direct_map_resource(struct device *dev, phys_addr_t paddr,
diff --git a/kernel/dma/direct.h b/kernel/dma/direct.h
index a78c0ba70645..e38ffc5e6bdd 100644
--- a/kernel/dma/direct.h
+++ b/kernel/dma/direct.h
@@ -8,6 +8,7 @@
#define _KERNEL_DMA_DIRECT_H

#include <linux/dma-direct.h>
+#include <linux/memremap.h>

int dma_direct_get_sgtable(struct device *dev, struct sg_table *sgt,
void *cpu_addr, dma_addr_t dma_addr, size_t size,
@@ -87,10 +88,15 @@ static inline dma_addr_t dma_direct_map_page(struct device *dev,
phys_addr_t phys = page_to_phys(page) + offset;
dma_addr_t dma_addr = phys_to_dma(dev, phys);

- if (is_swiotlb_force_bounce(dev))
+ if (is_swiotlb_force_bounce(dev)) {
+ if (is_pci_p2pdma_page(page))
+ return DMA_MAPPING_ERROR;
return swiotlb_map(dev, phys, size, dir, attrs);
+ }

if (unlikely(!dma_capable(dev, dma_addr, size, true))) {
+ if (is_pci_p2pdma_page(page))
+ return DMA_MAPPING_ERROR;
if (is_swiotlb_active(dev))
return swiotlb_map(dev, phys, size, dir, attrs);

--
2.30.2