From: John Hubbard <jhubbard@nvidia.com>
To: Logan Gunthorpe <logang@deltatee.com>,
<linux-kernel@vger.kernel.org>, <linux-nvme@lists.infradead.org>,
<linux-block@vger.kernel.org>, <linux-pci@vger.kernel.org>,
<linux-mm@kvack.org>, <iommu@lists.linux-foundation.org>
Cc: "Stephen Bates" <sbates@raithlin.com>,
"Christoph Hellwig" <hch@lst.de>,
"Dan Williams" <dan.j.williams@intel.com>,
"Jason Gunthorpe" <jgg@ziepe.ca>,
"Christian König" <christian.koenig@amd.com>,
"Don Dutile" <ddutile@redhat.com>,
"Matthew Wilcox" <willy@infradead.org>,
"Daniel Vetter" <daniel.vetter@ffwll.ch>,
"Jakowski Andrzej" <andrzej.jakowski@intel.com>,
"Minturn Dave B" <dave.b.minturn@intel.com>,
"Jason Ekstrand" <jason@jlekstrand.net>,
"Dave Hansen" <dave.hansen@linux.intel.com>,
"Xiong Jianxin" <jianxin.xiong@intel.com>,
"Bjorn Helgaas" <helgaas@kernel.org>,
"Ira Weiny" <ira.weiny@intel.com>,
"Robin Murphy" <robin.murphy@arm.com>
Subject: Re: [PATCH 08/16] PCI/P2PDMA: Introduce helpers for dma_map_sg implementations
Date: Sun, 2 May 2021 17:50:39 -0700 [thread overview]
Message-ID: <e27d35f8-5c3a-39e3-9845-6d2bf15cc8b3@nvidia.com> (raw)
In-Reply-To: <20210408170123.8788-9-logang@deltatee.com>
On 4/8/21 10:01 AM, 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.
>
OK, coming back to this patch, after seeing how it is used later in
the series...
> 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 <logang@deltatee.com>
> ---
> drivers/pci/p2pdma.c | 65 ++++++++++++++++++++++++++++++++++++++
> include/linux/pci-p2pdma.h | 21 ++++++++++++
> 2 files changed, 86 insertions(+)
>
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 38c93f57a941..44ad7664e875 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -923,6 +923,71 @@ 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 on the stack outside of
> + * the for_each_sg() loop and initialized to zero.
Silly fine point for the docs here: it doesn't actually have to be on
the stack, so I don't think you need to write that constraint in the
documentation. It just has be be somehow allocated and zeroed.
> + * @dev: DMA device that's doing the mapping operation
> + * @sg: scatterlist segment to map
> + * @attrs: dma mapping attributes
> + *
> + * 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.
Should this be backed up with actual checks in the function, that
the prerequisites are met?
> + *
> + * Returns 1 if the segment was mapped, 0 if the segment should be mapped
> + * directly (or through the IOMMU) and -EREMOTEIO if the segment should not
> + * be mapped at all.
> + */
> +int pci_p2pdma_map_segment(struct pci_p2pdma_map_state *state,
> + struct device *dev, struct scatterlist *sg,
> + unsigned long dma_attrs)
> +{
> + if (state->pgmap != sg_page(sg)->pgmap) {
> + state->pgmap = sg_page(sg)->pgmap;
> + state->map = pci_p2pdma_map_type(state->pgmap, dev, dma_attrs);
> + state->bus_off = to_p2p_pgmap(state->pgmap)->bus_offset;
> + }
I'll quote myself from patch 9, because I had a comment there that actually
was meant for this patch:
Is it worth putting this stuff on the caller's stack? I mean, is there a
noticeable performance improvement from caching the state? Because if
it's invisible, then simplicity is better. I suspect you're right, and
that it *is* worth it, but it's good to know for real.
> +
> + switch (state->map) {
> + case PCI_P2PDMA_MAP_BUS_ADDR:
> + sg->dma_address = sg_phys(sg) + state->bus_off;
> + sg_dma_len(sg) = sg->length;
> + sg_mark_pci_p2pdma(sg);
> + return 1;
> + case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:
> + return 0;
> + default:
> + return -EREMOTEIO;
> + }
> +}
> +
> +/**
> + * pci_p2pdma_map_bus_segment - map an sg segment pre determined to
> + * be mapped with PCI_P2PDMA_MAP_BUS_ADDR
Or:
* pci_p2pdma_map_bus_segment - map an SG segment that is already known
* to be mapped with PCI_P2PDMA_MAP_BUS_ADDR
Also, should that prerequisite be backed up with checks in the function?
> + * @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.
Another prerequisite, so same question: do you think that the code should
also check that this prerequisite is met?
thanks,
--
John Hubbard
NVIDIA
> + */
> +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_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 a06072ac3a52..49e7679403cf 100644
> --- a/include/linux/pci-p2pdma.h
> +++ b/include/linux/pci-p2pdma.h
> @@ -13,6 +13,12 @@
>
> #include <linux/pci.h>
>
> +struct pci_p2pdma_map_state {
> + struct dev_pagemap *pgmap;
> + int map;
> + u64 bus_off;
> +};
> +
> struct block_device;
> struct scatterlist;
>
> @@ -43,6 +49,11 @@ 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);
> +int pci_p2pdma_map_segment(struct pci_p2pdma_map_state *state,
> + struct device *dev, struct scatterlist *sg,
> + unsigned long dma_attrs);
> +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,
> @@ -109,6 +120,16 @@ static inline void pci_p2pdma_unmap_sg_attrs(struct device *dev,
> unsigned long attrs)
> {
> }
> +static inline int pci_p2pdma_map_segment(struct pci_p2pdma_map_state *state,
> + struct device *dev, struct scatterlist *sg,
> + unsigned long dma_attrs)
> +{
> + return 0;
> +}
> +static inline void pci_p2pdma_map_bus_segment(struct scatterlist *pg_sg,
> + struct scatterlist *dma_sg)
> +{
> +}
> static inline int pci_p2pdma_enable_store(const char *page,
> struct pci_dev **p2p_dev, bool *use_p2pdma)
> {
>
next prev parent reply other threads:[~2021-05-03 0:51 UTC|newest]
Thread overview: 99+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-08 17:01 [PATCH 00/16] Add new DMA mapping operation for P2PDMA Logan Gunthorpe
2021-04-08 17:01 ` [PATCH 01/16] PCI/P2PDMA: Pass gfp_mask flags to upstream_bridge_distance_warn() Logan Gunthorpe
2021-05-02 3:58 ` John Hubbard
2021-05-03 15:57 ` Logan Gunthorpe
2021-05-03 18:17 ` John Hubbard
2021-05-03 18:20 ` Logan Gunthorpe
2021-05-03 18:23 ` John Hubbard
2021-05-03 18:24 ` Christoph Hellwig
2021-05-11 16:05 ` Don Dutile
2021-05-11 16:12 ` Logan Gunthorpe
2021-05-11 16:23 ` Don Dutile
2021-04-08 17:01 ` [PATCH 02/16] PCI/P2PDMA: Avoid pci_get_slot() which sleeps Logan Gunthorpe
2021-05-02 5:35 ` John Hubbard
2021-05-03 16:08 ` Logan Gunthorpe
2021-05-03 18:20 ` John Hubbard
2021-05-03 18:25 ` Christoph Hellwig
2021-05-11 16:05 ` Don Dutile
2021-05-11 16:16 ` Logan Gunthorpe
2021-05-11 16:05 ` Don Dutile
2021-05-11 16:14 ` Logan Gunthorpe
2021-04-08 17:01 ` [PATCH 03/16] PCI/P2PDMA: Attempt to set map_type if it has not been set Logan Gunthorpe
2021-05-02 19:58 ` John Hubbard
2021-05-03 16:17 ` Logan Gunthorpe
2021-05-03 18:22 ` John Hubbard
2021-05-03 18:35 ` Christoph Hellwig
2021-05-03 18:46 ` Logan Gunthorpe
2021-05-11 16:05 ` Don Dutile
2021-04-08 17:01 ` [PATCH 04/16] PCI/P2PDMA: Refactor pci_p2pdma_map_type() to take pagmap and device Logan Gunthorpe
2021-05-02 20:41 ` John Hubbard
2021-05-03 16:30 ` Logan Gunthorpe
2021-05-03 18:31 ` John Hubbard
2021-05-03 18:56 ` Logan Gunthorpe
2021-05-03 21:54 ` John Hubbard
2021-05-03 22:57 ` Jason Gunthorpe
2021-05-03 23:40 ` John Hubbard
2021-04-08 17:01 ` [PATCH 05/16] dma-mapping: Introduce dma_map_sg_p2pdma() Logan Gunthorpe
2021-04-27 19:22 ` Jason Gunthorpe
2021-04-27 22:49 ` Logan Gunthorpe
2021-04-27 19:31 ` Jason Gunthorpe
2021-04-27 22:55 ` Logan Gunthorpe
2021-04-27 23:01 ` Jason Gunthorpe
2021-05-03 18:28 ` Christoph Hellwig
2021-05-03 18:31 ` Logan Gunthorpe
2021-05-02 21:23 ` John Hubbard
2021-05-03 16:38 ` Logan Gunthorpe
2021-05-11 16:05 ` Don Dutile
2021-04-08 17:01 ` [PATCH 06/16] lib/scatterlist: Add flag for indicating P2PDMA segments in an SGL Logan Gunthorpe
2021-05-02 22:34 ` John Hubbard
2021-04-08 17:01 ` [PATCH 07/16] PCI/P2PDMA: Make pci_p2pdma_map_type() non-static Logan Gunthorpe
2021-05-02 22:44 ` John Hubbard
2021-05-03 16:39 ` Logan Gunthorpe
2021-05-11 16:06 ` Don Dutile
2021-05-11 16:17 ` Logan Gunthorpe
2021-04-08 17:01 ` [PATCH 08/16] PCI/P2PDMA: Introduce helpers for dma_map_sg implementations Logan Gunthorpe
2021-05-02 22:52 ` John Hubbard
2021-05-03 0:50 ` John Hubbard [this message]
2021-05-03 17:15 ` Logan Gunthorpe
2021-04-08 17:01 ` [PATCH 09/16] dma-direct: Support PCI P2PDMA pages in dma-direct map_sg Logan Gunthorpe
2021-04-27 19:33 ` Jason Gunthorpe
2021-04-27 19:40 ` Jason Gunthorpe
2021-04-27 22:56 ` Logan Gunthorpe
2021-05-02 23:28 ` John Hubbard
2021-05-02 23:32 ` John Hubbard
2021-05-03 17:06 ` Logan Gunthorpe
2021-05-03 16:55 ` Logan Gunthorpe
2021-05-04 0:12 ` John Hubbard
2021-05-03 17:04 ` Logan Gunthorpe
2021-05-04 0:01 ` John Hubbard
2021-04-08 17:01 ` [PATCH 10/16] dma-mapping: Add flags to dma_map_ops to indicate PCI P2PDMA support Logan Gunthorpe
2021-05-03 0:32 ` John Hubbard
2021-05-03 17:09 ` Logan Gunthorpe
2021-05-11 16:06 ` Don Dutile
2021-05-11 16:19 ` Logan Gunthorpe
2021-04-08 17:01 ` [PATCH 11/16] iommu/dma: Support PCI P2PDMA pages in dma-iommu map_sg Logan Gunthorpe
2021-04-27 19:43 ` Jason Gunthorpe
2021-04-27 22:59 ` Logan Gunthorpe
2021-05-03 1:14 ` John Hubbard
2021-05-06 23:59 ` Logan Gunthorpe
2021-05-11 16:06 ` Don Dutile
2021-05-11 16:35 ` Logan Gunthorpe
2021-04-08 17:01 ` [PATCH 12/16] nvme-pci: Check DMA ops when indicating support for PCI P2PDMA Logan Gunthorpe
2021-05-03 1:29 ` John Hubbard
2021-05-03 17:17 ` Logan Gunthorpe
2021-05-04 0:17 ` John Hubbard
2021-04-08 17:01 ` [PATCH 13/16] nvme-pci: Convert to using dma_map_sg_p2pdma for p2pdma pages Logan Gunthorpe
2021-05-03 1:34 ` John Hubbard
2021-05-03 17:19 ` Logan Gunthorpe
2021-05-04 0:26 ` John Hubbard
2021-04-08 17:01 ` [PATCH 14/16] nvme-rdma: Ensure dma support when using p2pdma Logan Gunthorpe
2021-04-27 19:47 ` Jason Gunthorpe
2021-04-27 22:59 ` Logan Gunthorpe
2021-05-03 1:37 ` John Hubbard
2021-04-08 17:01 ` [PATCH 15/16] RDMA/rw: use dma_map_sg_p2pdma() Logan Gunthorpe
2021-04-08 17:01 ` [PATCH 16/16] PCI/P2PDMA: Remove pci_p2pdma_[un]map_sg() Logan Gunthorpe
2021-04-27 19:28 ` [PATCH 00/16] Add new DMA mapping operation for P2PDMA Jason Gunthorpe
2021-04-27 20:21 ` John Hubbard
2021-04-27 20:48 ` Dan Williams
2021-05-02 1:22 ` John Hubbard
2021-05-11 16:05 ` Don Dutile
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