lkml.org 
[lkml]   [2020]   [Jul]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 1/4] dma-mapping: Add bounced DMA ops
From
Date
On 2020-07-13 10:12, Claire Chang wrote:
> The bounced DMA ops provide an implementation of DMA ops that bounce
> streaming DMA in and out of a specially allocated region. Only the
> operations relevant to streaming DMA are supported.

I think there are too many implicit assumptions here - apparently that
coherent allocations will always be intercepted by
dma_*_from_dev_coherent(), and that calling into dma-direct won't
actually bounce things a second time beyond where you thought they were
going, manage coherency for a different address, and make it all go
subtly wrong. Consider "swiotlb=force", for instance...

Again, plumbing this straight into dma-direct so that SWIOTLB can simply
target a different buffer and always bounce regardless of masks would
seem a far better option.

Robin.

> Signed-off-by: Claire Chang <tientzu@chromium.org>
> ---
> include/linux/device.h | 3 +
> include/linux/dma-mapping.h | 1 +
> kernel/dma/Kconfig | 17 +++
> kernel/dma/Makefile | 1 +
> kernel/dma/bounced.c | 215 ++++++++++++++++++++++++++++++++++++
> 5 files changed, 237 insertions(+)
> create mode 100644 kernel/dma/bounced.c
>
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 7322c51e9c0c..868b9a364003 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -588,6 +588,9 @@ struct device {
>
> struct list_head dma_pools; /* dma pools (if dma'ble) */
>
> +#ifdef CONFIG_DMA_BOUNCED
> + struct dma_bounced_mem *dma_bounced_mem;
> +#endif
> #ifdef CONFIG_DMA_DECLARE_COHERENT
> struct dma_coherent_mem *dma_mem; /* internal for coherent mem
> override */
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index 2328f451a45d..86089424dafd 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -135,6 +135,7 @@ struct dma_map_ops {
>
> extern const struct dma_map_ops dma_virt_ops;
> extern const struct dma_map_ops dma_dummy_ops;
> +extern const struct dma_map_ops dma_bounced_ops;
>
> #define DMA_BIT_MASK(n) (((n) == 64) ? ~0ULL : ((1ULL<<(n))-1))
>
> diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
> index 1da3f44f2565..148734c8748b 100644
> --- a/kernel/dma/Kconfig
> +++ b/kernel/dma/Kconfig
> @@ -88,6 +88,23 @@ config DMA_DIRECT_REMAP
> select DMA_REMAP
> select DMA_COHERENT_POOL
>
> +config DMA_BOUNCED
> + bool "DMA Bounced"
> + depends on !HIGHMEM
> + select OF_RESERVED_MEM
> + help
> + This enables support for bounced DMA pools which provide a level of
> + DMA memory protection on systems with limited hardware protection
> + capabilities, such as those lacking an IOMMU. It does so by bouncing
> + the data to a specially allocated DMA-accessible protected region
> + before mapping and unmapping. One can assign the protected memory
> + region in the device tree by using reserved-memory.
> +
> + For more information see
> + <Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt>
> + and <kernel/dma/bounced.c>.
> + If unsure, say "n".
> +
> config DMA_CMA
> bool "DMA Contiguous Memory Allocator"
> depends on HAVE_DMA_CONTIGUOUS && CMA
> diff --git a/kernel/dma/Makefile b/kernel/dma/Makefile
> index 370f63344e9c..f5fb4f42326a 100644
> --- a/kernel/dma/Makefile
> +++ b/kernel/dma/Makefile
> @@ -1,6 +1,7 @@
> # SPDX-License-Identifier: GPL-2.0
>
> obj-$(CONFIG_HAS_DMA) += mapping.o direct.o dummy.o
> +obj-$(CONFIG_DMA_BOUNCED) += bounced.o
> obj-$(CONFIG_DMA_CMA) += contiguous.o
> obj-$(CONFIG_DMA_DECLARE_COHERENT) += coherent.o
> obj-$(CONFIG_DMA_VIRT_OPS) += virt.o
> diff --git a/kernel/dma/bounced.c b/kernel/dma/bounced.c
> new file mode 100644
> index 000000000000..fcaabb5eccf2
> --- /dev/null
> +++ b/kernel/dma/bounced.c
> @@ -0,0 +1,215 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Bounced DMA support.
> + *
> + * This implements the mitigations for lack of IOMMU by bouncing the data to a
> + * specially allocated region before mapping and unmapping.
> + *
> + * Copyright 2020 Google LLC.
> + */
> +#include <linux/dma-direct.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/dma-noncoherent.h>
> +#include <linux/io.h>
> +#include <linux/genalloc.h>
> +#include <linux/slab.h>
> +
> +struct dma_bounced_mem {
> + void **orig_addr;
> + void *virt_base;
> + dma_addr_t device_base;
> + dma_addr_t device_end;
> + struct gen_pool *pool;
> + size_t size;
> +};
> +
> +static void dma_bounced_set_orig_virt(struct device *dev, dma_addr_t dma_addr,
> + void *orig_addr)
> +{
> + struct dma_bounced_mem *mem = dev->dma_bounced_mem;
> + int idx = (dma_addr - mem->device_base) >> PAGE_SHIFT;
> +
> + if (dma_addr < mem->device_base || dma_addr >= mem->device_end)
> + return;
> +
> + mem->orig_addr[idx] = orig_addr;
> +}
> +
> +static void *dma_bounced_get_orig_virt(struct device *dev, dma_addr_t dma_addr)
> +{
> + struct dma_bounced_mem *mem = dev->dma_bounced_mem;
> + int idx = (dma_addr - mem->device_base) >> PAGE_SHIFT;
> +
> + if (dma_addr < mem->device_base || dma_addr >= mem->device_end)
> + return NULL;
> +
> + return mem->orig_addr[idx];
> +}
> +
> +static void *dma_bounced_get_virt(struct device *dev, dma_addr_t dma_addr)
> +{
> + struct dma_bounced_mem *mem = dev->dma_bounced_mem;
> +
> + if (dma_addr < mem->device_base || dma_addr >= mem->device_end)
> + return NULL;
> +
> + return (dma_addr - mem->device_base) + mem->virt_base;
> +}
> +
> +static void dma_bounced_sync_single_for_cpu(struct device *dev,
> + dma_addr_t dma_addr, size_t size,
> + enum dma_data_direction dir)
> +{
> + void *orig_virt = dma_bounced_get_orig_virt(dev, dma_addr);
> + void *bounced_virt = dma_bounced_get_virt(dev, dma_addr);
> +
> + if (!orig_virt || !bounced_virt)
> + return;
> +
> + dma_direct_sync_single_for_cpu(dev, dma_addr, size, dir);
> +
> + if (dir == DMA_FROM_DEVICE || dir == DMA_BIDIRECTIONAL)
> + memcpy(orig_virt, bounced_virt, size);
> +}
> +
> +static void dma_bounced_sync_single_for_device(struct device *dev,
> + dma_addr_t dma_addr, size_t size,
> + enum dma_data_direction dir)
> +{
> + void *orig_virt = dma_bounced_get_orig_virt(dev, dma_addr);
> + void *bounced_virt = dma_bounced_get_virt(dev, dma_addr);
> +
> + if (!orig_virt || !bounced_virt)
> + return;
> +
> + if (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)
> + memcpy(bounced_virt, orig_virt, size);
> +
> + dma_direct_sync_single_for_device(dev, dma_addr, size, dir);
> +}
> +
> +static void dma_bounced_sync_sg_for_cpu(struct device *dev,
> + struct scatterlist *sgl, int nents,
> + enum dma_data_direction dir)
> +{
> + struct scatterlist *sg;
> + int i;
> +
> + for_each_sg(sgl, sg, nents, i) {
> + dma_bounced_sync_single_for_cpu(dev, sg->dma_address,
> + sg->length, dir);
> + }
> +}
> +
> +static void dma_bounced_sync_sg_for_device(struct device *dev,
> + struct scatterlist *sgl, int nents,
> + enum dma_data_direction dir)
> +{
> + struct scatterlist *sg;
> + int i;
> +
> + for_each_sg(sgl, sg, nents, i) {
> + dma_bounced_sync_single_for_device(dev, sg->dma_address,
> + sg->length, dir);
> + }
> +}
> +
> +static void dma_bounced_unmap_page(struct device *dev, dma_addr_t dma_addr,
> + size_t size, enum dma_data_direction dir,
> + unsigned long attrs)
> +{
> + struct dma_bounced_mem *mem = dev->dma_bounced_mem;
> +
> + if (dma_addr < mem->device_base || dma_addr >= mem->device_end)
> + return;
> +
> + if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
> + dma_bounced_sync_single_for_cpu(dev, dma_addr, size, dir);
> +
> + dma_bounced_set_orig_virt(dev, dma_addr, NULL);
> + gen_pool_free(mem->pool,
> + (unsigned long)dma_bounced_get_virt(dev, dma_addr), size);
> +}
> +
> +static dma_addr_t dma_bounced_map_page(struct device *dev, struct page *page,
> + unsigned long offset, size_t size,
> + enum dma_data_direction dir,
> + unsigned long attrs)
> +{
> + struct dma_bounced_mem *mem = dev->dma_bounced_mem;
> + dma_addr_t dma_addr;
> + void *orig_virt;
> +
> + if (unlikely(!gen_pool_dma_alloc(mem->pool, size, &dma_addr)))
> + return DMA_MAPPING_ERROR;
> +
> + orig_virt = page_to_virt(page) + offset;
> + dma_bounced_set_orig_virt(dev, dma_addr, orig_virt);
> +
> + if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
> + dma_bounced_sync_single_for_device(dev, dma_addr, size, dir);
> +
> + return dma_addr;
> +}
> +
> +static void dma_bounced_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_bounced_unmap_page(dev, sg->dma_address, sg_dma_len(sg),
> + dir, attrs);
> + }
> +}
> +
> +static int dma_bounced_map_sg(struct device *dev, struct scatterlist *sgl,
> + int nents, enum dma_data_direction dir,
> + unsigned long attrs)
> +{
> + int i;
> + struct scatterlist *sg;
> +
> + for_each_sg(sgl, sg, nents, i) {
> + sg->dma_address = dma_bounced_map_page(
> + dev, sg_page(sg), sg->offset, sg->length, dir, attrs);
> + if (sg->dma_address == DMA_MAPPING_ERROR)
> + goto out_unmap;
> + sg_dma_len(sg) = sg->length;
> + }
> +
> + return nents;
> +
> +out_unmap:
> + dma_bounced_unmap_sg(dev, sgl, i, dir, attrs | DMA_ATTR_SKIP_CPU_SYNC);
> + return 0;
> +}
> +
> +static size_t dma_bounced_max_mapping_size(struct device *dev)
> +{
> + return dev->dma_bounced_mem->size;
> +}
> +
> +const struct dma_map_ops dma_bounced_ops = {
> + .alloc = NULL,
> + .free = NULL,
> + .mmap = NULL,
> + .get_sgtable = NULL,
> + .sync_single_for_cpu = dma_bounced_sync_single_for_cpu,
> + .sync_single_for_device = dma_bounced_sync_single_for_device,
> + .sync_sg_for_cpu = dma_bounced_sync_sg_for_cpu,
> + .sync_sg_for_device = dma_bounced_sync_sg_for_device,
> + .map_page = dma_bounced_map_page,
> + .unmap_page = dma_bounced_unmap_page,
> + .map_sg = dma_bounced_map_sg,
> + .unmap_sg = dma_bounced_unmap_sg,
> + .unmap_resource = NULL,
> + .map_resource = NULL,
> + .cache_sync = NULL,
> + .dma_supported = dma_direct_supported,
> + .get_required_mask = dma_direct_get_required_mask,
> + .max_mapping_size = dma_bounced_max_mapping_size,
> + .get_merge_boundary = NULL,
> +};
>

\
 
 \ /
  Last update: 2020-07-13 13:56    [W:0.119 / U:1.020 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site