Re: [PATCH v3 04/20] PCI/P2PDMA: introduce helpers for dma_map_sg implementations
On 2021-09-28 12:55 p.m., Jason Gunthorpe wrote:
> On Thu, Sep 16, 2021 at 05:40:44PM -0600, Logan Gunthorpe wrote:
>> Add pci_p2pdma_map_segment() as a helper for simple dma_map_sg()
>> implementations. It takes an scatterlist segment that must point to a
>> pci_p2pdma struct page and will map it if the mapping requires a bus
>> address.
>>
>> The return value indicates whether the mapping required a bus address
>> or whether the caller still needs to map the segment normally. If the
>> segment should not be mapped, -EREMOTEIO is returned.
>>
>> This helper uses a state structure to track the changes to the
>> pgmap across calls and avoid needing to lookup into the xarray for
>> every page.
>>
>> Also add pci_p2pdma_map_bus_segment() which is useful for IOMMU
>> dma_map_sg() implementations where the sg segment containing the page
>> differs from the sg segment containing the DMA address.
>>
>> Signed-off-by: Logan Gunthorpe
>> drivers/pci/p2pdma.c | 59 ++
>> include/linux/pci-p2pdma.h | 21 ++
>> 2 files changed, 80 insertions(+)
>>
>> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
>> index b656d8c801a7..58c34f1f1473 100644
>> +++ b/drivers/pci/p2pdma.c
>> @@ -943,6 +943,65 @@ void pci_p2pdma_unmap_sg_attrs(struct device *dev,
>> struct scatterlist *sg,
>> }
>> EXPORT_SYMBOL_GPL(pci_p2pdma_unmap_sg_attrs);
>>
>> +/**
>> + * 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)
>> +{
>> +if (state->pgmap != sg_page(sg)->pgmap) {
>> +state->pgmap = sg_page(sg)->pgmap;
>> +state->map = pci_p2pdma_map_type(state->pgmap, dev);
>> +state->bus_off = to_p2p_pgmap(state->pgmap)->bus_offset;
>> +}
>
> Is this safe? I was just talking with Joao about this,
>
> https://lore.kernel.org/r/20210928180150.gi3544...@ziepe.ca
>
I agree that taking the extra reference on the pagemap seems
unnecessary. However, it was convenient for the purposes of this
patchset to not have to check the page type for every page and only on
every new page map. But if we need to add a check directly to gup,
that'd probably be fine too.
> API wise I absolutely think this should be safe as written, but is it
> really?
>
> Does pgmap ensure that a positive refcount struct page always has a
> valid pgmap pointer (and thus the mess in gup can be deleted) or does
> this need to get the pgmap as well to keep it alive?
Yes, the P2PDMA code ensures that the pgmap will not be deleted if there
is a positive refcount on any struct page.
LOgan
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Re: [PATCH v3 04/20] PCI/P2PDMA: introduce helpers for dma_map_sg implementations
On Thu, Sep 16, 2021 at 05:40:44PM -0600, Logan Gunthorpe wrote:
> Add pci_p2pdma_map_segment() as a helper for simple dma_map_sg()
> implementations. It takes an scatterlist segment that must point to a
> pci_p2pdma struct page and will map it if the mapping requires a bus
> address.
>
> The return value indicates whether the mapping required a bus address
> or whether the caller still needs to map the segment normally. If the
> segment should not be mapped, -EREMOTEIO is returned.
>
> This helper uses a state structure to track the changes to the
> pgmap across calls and avoid needing to lookup into the xarray for
> every page.
>
> Also add pci_p2pdma_map_bus_segment() which is useful for IOMMU
> dma_map_sg() implementations where the sg segment containing the page
> differs from the sg segment containing the DMA address.
>
> Signed-off-by: Logan Gunthorpe
> drivers/pci/p2pdma.c | 59 ++
> include/linux/pci-p2pdma.h | 21 ++
> 2 files changed, 80 insertions(+)
>
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index b656d8c801a7..58c34f1f1473 100644
> +++ b/drivers/pci/p2pdma.c
> @@ -943,6 +943,65 @@ void pci_p2pdma_unmap_sg_attrs(struct device *dev,
> struct scatterlist *sg,
> }
> EXPORT_SYMBOL_GPL(pci_p2pdma_unmap_sg_attrs);
>
> +/**
> + * 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)
> +{
> + if (state->pgmap != sg_page(sg)->pgmap) {
> + state->pgmap = sg_page(sg)->pgmap;
> + state->map = pci_p2pdma_map_type(state->pgmap, dev);
> + state->bus_off = to_p2p_pgmap(state->pgmap)->bus_offset;
> + }
Is this safe? I was just talking with Joao about this,
https://lore.kernel.org/r/20210928180150.gi3544...@ziepe.ca
API wise I absolutely think this should be safe as written, but is it
really?
Does pgmap ensure that a positive refcount struct page always has a
valid pgmap pointer (and thus the mess in gup can be deleted) or does
this need to get the pgmap as well to keep it alive?
Jason
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Re: [PATCH v3 04/20] PCI/P2PDMA: introduce helpers for dma_map_sg implementations
On 2021-09-27 12:53 p.m., Bjorn Helgaas wrote: > Acked-by: Bjorn Helgaas > > Ditto. Thanks Bjorn, I'll make these changes and add your Acks for subsequent postings. Logan ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH v3 04/20] PCI/P2PDMA: introduce helpers for dma_map_sg implementations
On Thu, Sep 16, 2021 at 05:40:44PM -0600, Logan Gunthorpe wrote:
> Add pci_p2pdma_map_segment() as a helper for simple dma_map_sg()
> implementations. It takes an scatterlist segment that must point to a
> pci_p2pdma struct page and will map it if the mapping requires a bus
> address.
>
> The return value indicates whether the mapping required a bus address
> or whether the caller still needs to map the segment normally. If the
> segment should not be mapped, -EREMOTEIO is returned.
>
> This helper uses a state structure to track the changes to the
> pgmap across calls and avoid needing to lookup into the xarray for
> every page.
>
> Also add pci_p2pdma_map_bus_segment() which is useful for IOMMU
> dma_map_sg() implementations where the sg segment containing the page
> differs from the sg segment containing the DMA address.
>
> Signed-off-by: Logan Gunthorpe
Acked-by: Bjorn Helgaas
Ditto.
> ---
> drivers/pci/p2pdma.c | 59 ++
> include/linux/pci-p2pdma.h | 21 ++
> 2 files changed, 80 insertions(+)
>
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index b656d8c801a7..58c34f1f1473 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -943,6 +943,65 @@ void pci_p2pdma_unmap_sg_attrs(struct device *dev,
> struct scatterlist *sg,
> }
> EXPORT_SYMBOL_GPL(pci_p2pdma_unmap_sg_attrs);
>
> +/**
> + * 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.
s/non-iommu/non-IOMMU/
> + *
> + * 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)
> +{
> + if (state->pgmap != sg_page(sg)->pgmap) {
> + state->pgmap = sg_page(sg)->pgmap;
> + 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_pci_p2pdma(sg);
> + }
> +
> + return state->map;
> +}
> +
> +/**
> + * pci_p2pdma_map_bus_segment - map an sg segment pre determined to
> + * be mapped with PCI_P2PDMA_MAP_BUS_ADDR
> + * @pg_sg: scatterlist segment with the page to map
> + * @dma_sg: scatterlist segment to assign a dma address to
s/dma address/DMA address/, also below
> + *
> + * This is a helper for iommu dma_map_sg() implementations when the
> + * segment for the dma address differs from the segment containing the
> + * source page.
> + *
> + * pci_p2pdma_map_type() must have already been called on the pg_sg and
> + * returned PCI_P2PDMA_MAP_BUS_ADDR.
> + */
> +void pci_p2pdma_map_bus_segment(struct scatterlist *pg_sg,
> + struct scatterlist *dma_sg)
> +{
> + struct pci_p2pdma_pagemap *pgmap = to_p2p_pgmap(sg_page(pg_sg)->pgmap);
> +
> + dma_sg->dma_address = sg_phys(pg_sg) + pgmap->bus_offset;
> + sg_dma_len(dma_sg) = pg_sg->length;
> + sg_dma_mark_pci_p2pdma(dma_sg);
> +}
> +
> /**
> * pci_p2pdma_enable_store - parse a configfs/sysfs attribute store
> * to enable p2pdma
> diff --git a/include/linux/pci-p2pdma.h b/include/linux/pci-p2pdma.h
> index caac2d023f8f..e5a8d5bc0f51 100644
> --- a/include/linux/pci-p2pdma.h
> +++ b/include/linux/pci-p2pdma.h
> @@ -13,6 +13,12 @@
>
> #include
>
> +struct pci_p2pdma_map_state {
> + struct dev_pagemap *pgmap;
> + int map;
> + u64 bus_off;
> +};
> +
> struct block_device;
> struct scatterlist;
>
> @@ -70,6 +76,11 @@ int pci_p2pdma_map_sg_attrs(struct device *dev, struct
> scatterlist *sg,
> int nents, enum dma_data_direction dir, unsigned long attrs);
> void pci_p2pdma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg,
> int nents, enum dma_data_direction dir, unsigned long attrs);
> +enum pci_p2pdma_map_type
> +pci_p2pdma_map_segment(struct pci_p2pdma_map_state *state, struct device
> *dev,
> +struct scatterlist *sg);
> +void pci_p2pdma_map_bus_segment(struct scatterlist *pg_sg,
> + struct scatterlist *dma_sg);
> int pci_p2pdma_enable_store(const
[PATCH v3 04/20] PCI/P2PDMA: introduce helpers for dma_map_sg implementations
Add pci_p2pdma_map_segment() as a helper for simple dma_map_sg()
implementations. It takes an scatterlist segment that must point to a
pci_p2pdma struct page and will map it if the mapping requires a bus
address.
The return value indicates whether the mapping required a bus address
or whether the caller still needs to map the segment normally. If the
segment should not be mapped, -EREMOTEIO is returned.
This helper uses a state structure to track the changes to the
pgmap across calls and avoid needing to lookup into the xarray for
every page.
Also add pci_p2pdma_map_bus_segment() which is useful for IOMMU
dma_map_sg() implementations where the sg segment containing the page
differs from the sg segment containing the DMA address.
Signed-off-by: Logan Gunthorpe
---
drivers/pci/p2pdma.c | 59 ++
include/linux/pci-p2pdma.h | 21 ++
2 files changed, 80 insertions(+)
diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index b656d8c801a7..58c34f1f1473 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -943,6 +943,65 @@ void pci_p2pdma_unmap_sg_attrs(struct device *dev, struct
scatterlist *sg,
}
EXPORT_SYMBOL_GPL(pci_p2pdma_unmap_sg_attrs);
+/**
+ * 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)
+{
+ if (state->pgmap != sg_page(sg)->pgmap) {
+ state->pgmap = sg_page(sg)->pgmap;
+ 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_pci_p2pdma(sg);
+ }
+
+ return state->map;
+}
+
+/**
+ * pci_p2pdma_map_bus_segment - map an sg segment pre determined to
+ * be mapped with PCI_P2PDMA_MAP_BUS_ADDR
+ * @pg_sg: scatterlist segment with the page to map
+ * @dma_sg: scatterlist segment to assign a dma address to
+ *
+ * This is a helper for iommu dma_map_sg() implementations when the
+ * segment for the dma address differs from the segment containing the
+ * source page.
+ *
+ * pci_p2pdma_map_type() must have already been called on the pg_sg and
+ * returned PCI_P2PDMA_MAP_BUS_ADDR.
+ */
+void pci_p2pdma_map_bus_segment(struct scatterlist *pg_sg,
+ struct scatterlist *dma_sg)
+{
+ struct pci_p2pdma_pagemap *pgmap = to_p2p_pgmap(sg_page(pg_sg)->pgmap);
+
+ dma_sg->dma_address = sg_phys(pg_sg) + pgmap->bus_offset;
+ sg_dma_len(dma_sg) = pg_sg->length;
+ sg_dma_mark_pci_p2pdma(dma_sg);
+}
+
/**
* pci_p2pdma_enable_store - parse a configfs/sysfs attribute store
* to enable p2pdma
diff --git a/include/linux/pci-p2pdma.h b/include/linux/pci-p2pdma.h
index caac2d023f8f..e5a8d5bc0f51 100644
--- a/include/linux/pci-p2pdma.h
+++ b/include/linux/pci-p2pdma.h
@@ -13,6 +13,12 @@
#include
+struct pci_p2pdma_map_state {
+ struct dev_pagemap *pgmap;
+ int map;
+ u64 bus_off;
+};
+
struct block_device;
struct scatterlist;
@@ -70,6 +76,11 @@ int pci_p2pdma_map_sg_attrs(struct device *dev, struct
scatterlist *sg,
int nents, enum dma_data_direction dir, unsigned long attrs);
void pci_p2pdma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg,
int nents, enum dma_data_direction dir, unsigned long attrs);
+enum pci_p2pdma_map_type
+pci_p2pdma_map_segment(struct pci_p2pdma_map_state *state, struct device *dev,
+ struct scatterlist *sg);
+void pci_p2pdma_map_bus_segment(struct scatterlist *pg_sg,
+ struct scatterlist *dma_sg);
int pci_p2pdma_enable_store(const char *page, struct pci_dev **p2p_dev,
bool *use_p2pdma);
ssize_t pci_p2pdma_enable_show(char *page, struct pci_dev *p2p_dev,
@@ -135,6 +146,16 @@ static inline void pci_p2pdma_unmap_sg_attrs(struct device
*dev,
unsigned long attrs)
{
}
+static inline enum pci_p2pdma_map_type
+pci_p2pdma_map_segment(struct
