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Message-ID: <a59daad2-31eb-b7b6-d68f-f42d717dbc2c@redhat.com>
Date: Tue, 11 May 2021 12:05:56 -0400
From: Don Dutile <ddutile@...hat.com>
To: Logan Gunthorpe <logang@...tatee.com>,
linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
linux-block@...r.kernel.org, linux-pci@...r.kernel.org,
linux-mm@...ck.org, iommu@...ts.linux-foundation.org
Cc: Stephen Bates <sbates@...thlin.com>,
Christoph Hellwig <hch@....de>,
Dan Williams <dan.j.williams@...el.com>,
Jason Gunthorpe <jgg@...pe.ca>,
Christian König <christian.koenig@....com>,
John Hubbard <jhubbard@...dia.com>,
Matthew Wilcox <willy@...radead.org>,
Daniel Vetter <daniel.vetter@...ll.ch>,
Jakowski Andrzej <andrzej.jakowski@...el.com>,
Minturn Dave B <dave.b.minturn@...el.com>,
Jason Ekstrand <jason@...kstrand.net>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Xiong Jianxin <jianxin.xiong@...el.com>,
Bjorn Helgaas <helgaas@...nel.org>,
Ira Weiny <ira.weiny@...el.com>,
Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 05/16] dma-mapping: Introduce dma_map_sg_p2pdma()
On 4/8/21 1:01 PM, Logan Gunthorpe wrote:
> dma_map_sg() either returns a positive number indicating the number
> of entries mapped or zero indicating that resources were not available
> to create the mapping. When zero is returned, it is always safe to retry
> the mapping later once resources have been freed.
>
> Once P2PDMA pages are mixed into the SGL there may be pages that may
> never be successfully mapped with a given device because that device may
> not actually be able to access those pages. Thus, multiple error
> conditions will need to be distinguished to determine weather a retry
s/weather/whether/
> is safe.
>
> Introduce dma_map_sg_p2pdma[_attrs]() with a different calling
> convention from dma_map_sg(). The function will return a positive
> integer on success or a negative errno on failure.
>
> ENOMEM will be used to indicate a resource failure and EREMOTEIO to
> indicate that a P2PDMA page is not mappable.
>
> The __DMA_ATTR_PCI_P2PDMA attribute is introduced to inform the lower
> level implementations that P2PDMA pages are allowed and to warn if a
> caller introduces them into the regular dma_map_sg() interface.
>
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
John caught any other comment I had (and more).
-dd
> ---
> include/linux/dma-mapping.h | 15 +++++++++++
> kernel/dma/mapping.c | 52 ++++++++++++++++++++++++++++++++-----
> 2 files changed, 61 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index 2a984cb4d1e0..50b8f586cf59 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -60,6 +60,12 @@
> * at least read-only at lesser-privileged levels).
> */
> #define DMA_ATTR_PRIVILEGED (1UL << 9)
> +/*
> + * __DMA_ATTR_PCI_P2PDMA: This should not be used directly, use
> + * dma_map_sg_p2pdma() instead. Used internally to indicate that the
> + * caller is using the dma_map_sg_p2pdma() interface.
> + */
> +#define __DMA_ATTR_PCI_P2PDMA (1UL << 10)
>
> /*
> * A dma_addr_t can hold any valid DMA or bus address for the platform. It can
> @@ -107,6 +113,8 @@ void dma_unmap_page_attrs(struct device *dev, dma_addr_t addr, size_t size,
> enum dma_data_direction dir, unsigned long attrs);
> int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents,
> enum dma_data_direction dir, unsigned long attrs);
> +int dma_map_sg_p2pdma_attrs(struct device *dev, struct scatterlist *sg,
> + int nents, enum dma_data_direction dir, unsigned long attrs);
> void dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg,
> int nents, enum dma_data_direction dir,
> unsigned long attrs);
> @@ -160,6 +168,12 @@ static inline int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg,
> {
> return 0;
> }
> +static inline int dma_map_sg_p2pdma_attrs(struct device *dev,
> + struct scatterlist *sg, int nents, enum dma_data_direction dir,
> + unsigned long attrs)
> +{
> + return 0;
> +}
> static inline void dma_unmap_sg_attrs(struct device *dev,
> struct scatterlist *sg, int nents, enum dma_data_direction dir,
> unsigned long attrs)
> @@ -392,6 +406,7 @@ static inline void dma_sync_sgtable_for_device(struct device *dev,
> #define dma_map_single(d, a, s, r) dma_map_single_attrs(d, a, s, r, 0)
> #define dma_unmap_single(d, a, s, r) dma_unmap_single_attrs(d, a, s, r, 0)
> #define dma_map_sg(d, s, n, r) dma_map_sg_attrs(d, s, n, r, 0)
> +#define dma_map_sg_p2pdma(d, s, n, r) dma_map_sg_p2pdma_attrs(d, s, n, r, 0)
> #define dma_unmap_sg(d, s, n, r) dma_unmap_sg_attrs(d, s, n, r, 0)
> #define dma_map_page(d, p, o, s, r) dma_map_page_attrs(d, p, o, s, r, 0)
> #define dma_unmap_page(d, a, s, r) dma_unmap_page_attrs(d, a, s, r, 0)
> diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
> index b6a633679933..923089c4267b 100644
> --- a/kernel/dma/mapping.c
> +++ b/kernel/dma/mapping.c
> @@ -177,12 +177,8 @@ void dma_unmap_page_attrs(struct device *dev, dma_addr_t addr, size_t size,
> }
> EXPORT_SYMBOL(dma_unmap_page_attrs);
>
> -/*
> - * dma_maps_sg_attrs returns 0 on error and > 0 on success.
> - * It should never return a value < 0.
> - */
> -int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents,
> - enum dma_data_direction dir, unsigned long attrs)
> +static int __dma_map_sg_attrs(struct device *dev, struct scatterlist *sg,
> + int nents, enum dma_data_direction dir, unsigned long attrs)
> {
> const struct dma_map_ops *ops = get_dma_ops(dev);
> int ents;
> @@ -197,6 +193,20 @@ int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents,
> ents = dma_direct_map_sg(dev, sg, nents, dir, attrs);
> else
> ents = ops->map_sg(dev, sg, nents, dir, attrs);
> +
> + return ents;
> +}
> +
> +/*
> + * dma_maps_sg_attrs returns 0 on error and > 0 on success.
> + * It should never return a value < 0.
> + */
> +int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents,
> + enum dma_data_direction dir, unsigned long attrs)
> +{
> + int ents;
> +
> + ents = __dma_map_sg_attrs(dev, sg, nents, dir, attrs);
> BUG_ON(ents < 0);
> debug_dma_map_sg(dev, sg, nents, ents, dir);
>
> @@ -204,6 +214,36 @@ int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents,
> }
> EXPORT_SYMBOL(dma_map_sg_attrs);
>
> +/*
> + * like dma_map_sg_attrs, but returns a negative errno on error (and > 0
> + * on success). This function must be used if PCI P2PDMA pages might
> + * be in the scatterlist.
> + *
> + * On error this function may return:
> + * -ENOMEM indicating that there was not enough resources available and
> + * the transfer may be retried later
> + * -EREMOTEIO indicating that P2PDMA pages were included but cannot
> + * be mapped by the specified device, retries will always fail
> + *
> + * The scatterlist should be unmapped with the regular dma_unmap_sg[_attrs]().
> + */
> +int dma_map_sg_p2pdma_attrs(struct device *dev, struct scatterlist *sg,
> + int nents, enum dma_data_direction dir, unsigned long attrs)
> +{
> + int ents;
> +
> + ents = __dma_map_sg_attrs(dev, sg, nents, dir,
> + attrs | __DMA_ATTR_PCI_P2PDMA);
> + if (!ents)
> + ents = -ENOMEM;
> +
> + if (ents > 0)
> + debug_dma_map_sg(dev, sg, nents, ents, dir);
> +
> + return ents;
> +}
> +EXPORT_SYMBOL_GPL(dma_map_sg_p2pdma_attrs);
> +
> void dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg,
> int nents, enum dma_data_direction dir,
> unsigned long attrs)
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