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PCI/P2PDMA: Refactor the p2pdma mapping helpers 

The current scheme with a single helper to determine the P2P status
and map a scatterlist segment force users to always use the map_sg
helper to DMA map, which we're trying to get away from because they
are very cache inefficient.

Refactor the code so that there is a single helper that checks the P2P
state for a page, including the result that it is not a P2P page to
simplify the callers, and a second one to perform the address translation
for a bus mapped P2P transfer that does not depend on the scatterlist
structure.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
This commit is contained in:
Christoph Hellwig 2025-05-05 10:01:38 +03:00 committed by Marek Szyprowski
parent 0af2f6be1b
commit a25e7962db
4 changed files with 91 additions and 88 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

47
drivers/iommu/dma-iommu.c
View File

@ -1359,7 +1359,6 @@ int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
struct scatterlist *s, *prev = NULL;
int prot = dma_info_to_prot(dir, dev_is_dma_coherent(dev), attrs);
struct pci_p2pdma_map_state p2pdma_state = {};
enum pci_p2pdma_map_type map;
dma_addr_t iova;
size_t iova_len = 0;
unsigned long mask = dma_get_seg_boundary(dev);
@ -1389,28 +1388,30 @@ int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
size_t s_length = s->length;
size_t pad_len = (mask - iova_len + 1) & mask;
if (is_pci_p2pdma_page(sg_page(s))) {
map = pci_p2pdma_map_segment(&p2pdma_state, dev, s);
switch (map) {
case PCI_P2PDMA_MAP_BUS_ADDR:
/*
* iommu_map_sg() will skip this segment as
* it is marked as a bus address,
* __finalise_sg() will copy the dma address
* into the output segment.
*/
continue;
case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
/*
* Mapping through host bridge should be
* mapped with regular IOVAs, thus we
* do nothing here and continue below.
*/
break;
default:
ret = -EREMOTEIO;
goto out_restore_sg;
}
switch (pci_p2pdma_state(&p2pdma_state, dev, sg_page(s))) {
case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
/*
* Mapping through host bridge should be mapped with
* regular IOVAs, thus we do nothing here and continue
* below.
*/
break;
case PCI_P2PDMA_MAP_NONE:
break;
case PCI_P2PDMA_MAP_BUS_ADDR:
/*
* iommu_map_sg() will skip this segment as it is marked
* as a bus address, __finalise_sg() will copy the dma
* address into the output segment.
*/
s->dma_address = pci_p2pdma_bus_addr_map(&p2pdma_state,
sg_phys(s));
sg_dma_len(s) = sg->length;
sg_dma_mark_bus_address(s);
continue;
default:
ret = -EREMOTEIO;
goto out_restore_sg;
}
sg_dma_address(s) = s_iova_off;

38
drivers/pci/p2pdma.c
View File

@ -1004,40 +1004,12 @@ static enum pci_p2pdma_map_type pci_p2pdma_map_type(struct dev_pagemap *pgmap,
return type;
}
/**
* pci_p2pdma_map_segment - map an sg segment determining the mapping type
* @state: State structure that should be declared outside of the for_each_sg()
* loop and initialized to zero.
* @dev: DMA device that's doing the mapping operation
* @sg: scatterlist segment to map
*
* This is a helper to be used by non-IOMMU dma_map_sg() implementations where
* the sg segment is the same for the page_link and the dma_address.
*
* Attempt to map a single segment in an SGL with the PCI bus address.
* The segment must point to a PCI P2PDMA page and thus must be
* wrapped in a is_pci_p2pdma_page(sg_page(sg)) check.
*
* Returns the type of mapping used and maps the page if the type is
* PCI_P2PDMA_MAP_BUS_ADDR.
*/
enum pci_p2pdma_map_type
pci_p2pdma_map_segment(struct pci_p2pdma_map_state *state, struct device *dev,
struct scatterlist *sg)
void __pci_p2pdma_update_state(struct pci_p2pdma_map_state *state,
struct device *dev, struct page *page)
{
if (state->pgmap != page_pgmap(sg_page(sg))) {
state->pgmap = page_pgmap(sg_page(sg));
state->map = pci_p2pdma_map_type(state->pgmap, dev);
state->bus_off = to_p2p_pgmap(state->pgmap)->bus_offset;
}
if (state->map == PCI_P2PDMA_MAP_BUS_ADDR) {
sg->dma_address = sg_phys(sg) + state->bus_off;
sg_dma_len(sg) = sg->length;
sg_dma_mark_bus_address(sg);
}
return state->map;
state->pgmap = page_pgmap(page);
state->map = pci_p2pdma_map_type(state->pgmap, dev);
state->bus_off = to_p2p_pgmap(state->pgmap)->bus_offset;
}
/**

51
include/linux/dma-map-ops.h
View File

@ -443,6 +443,11 @@ enum pci_p2pdma_map_type {
*/
PCI_P2PDMA_MAP_UNKNOWN = 0,
/*
* Not a PCI P2PDMA transfer.
*/
PCI_P2PDMA_MAP_NONE,
/*
* PCI_P2PDMA_MAP_NOT_SUPPORTED: Indicates the transaction will
* traverse the host bridge and the host bridge is not in the
@ -471,21 +476,47 @@ enum pci_p2pdma_map_type {
struct pci_p2pdma_map_state {
struct dev_pagemap *pgmap;
int map;
enum pci_p2pdma_map_type map;
u64 bus_off;
};
#ifdef CONFIG_PCI_P2PDMA
enum pci_p2pdma_map_type
pci_p2pdma_map_segment(struct pci_p2pdma_map_state *state, struct device *dev,
struct scatterlist *sg);
#else /* CONFIG_PCI_P2PDMA */
/* helper for pci_p2pdma_state(), do not use directly */
void __pci_p2pdma_update_state(struct pci_p2pdma_map_state *state,
struct device *dev, struct page *page);
/**
* pci_p2pdma_state - check the P2P transfer state of a page
* @state: P2P state structure
* @dev: device to transfer to/from
* @page: page to map
*
* Check if @page is a PCI P2PDMA page, and if yes of what kind. Returns the
* map type, and updates @state with all information needed for a P2P transfer.
*/
static inline enum pci_p2pdma_map_type
pci_p2pdma_map_segment(struct pci_p2pdma_map_state *state, struct device *dev,
struct scatterlist *sg)
pci_p2pdma_state(struct pci_p2pdma_map_state *state, struct device *dev,
struct page *page)
{
return PCI_P2PDMA_MAP_NOT_SUPPORTED;
if (IS_ENABLED(CONFIG_PCI_P2PDMA) && is_pci_p2pdma_page(page)) {
if (state->pgmap != page_pgmap(page))
__pci_p2pdma_update_state(state, dev, page);
return state->map;
}
return PCI_P2PDMA_MAP_NONE;
}
/**
* pci_p2pdma_bus_addr_map - map a PCI_P2PDMA_MAP_BUS_ADDR P2P transfer
* @state: P2P state structure
* @paddr: physical address to map
*
* Map a physically contiguous PCI_P2PDMA_MAP_BUS_ADDR transfer.
*/
static inline dma_addr_t
pci_p2pdma_bus_addr_map(struct pci_p2pdma_map_state *state, phys_addr_t paddr)
{
WARN_ON_ONCE(state->map != PCI_P2PDMA_MAP_BUS_ADDR);
return paddr + state->bus_off;
}
#endif /* CONFIG_PCI_P2PDMA */
#endif /* _LINUX_DMA_MAP_OPS_H */

43
kernel/dma/direct.c
View File

@ -462,34 +462,33 @@ int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
enum dma_data_direction dir, unsigned long attrs)
{
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;
switch (pci_p2pdma_state(&p2pdma_state, dev, sg_page(sg))) {
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.
*/
break;
case PCI_P2PDMA_MAP_NONE:
sg->dma_address = dma_direct_map_page(dev, sg_page(sg),
sg->offset, sg->length, dir, attrs);
if (sg->dma_address == DMA_MAPPING_ERROR) {
ret = -EIO;
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) {
ret = -EIO;
break;
case PCI_P2PDMA_MAP_BUS_ADDR:
sg->dma_address = pci_p2pdma_bus_addr_map(&p2pdma_state,
sg_phys(sg));
sg_dma_mark_bus_address(sg);
continue;
default:
ret = -EREMOTEIO;
goto out_unmap;
}
sg_dma_len(sg) = sg->length;