Re: [PATCH v13 09/12] swiotlb: Add restricted DMA alloc/free support

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 17 Jun 2021, Claire Chang wrote:
> Add the functions, swiotlb_{alloc,free} and is_swiotlb_for_alloc to
> support the memory allocation from restricted DMA pool.
> 
> The restricted DMA pool is preferred if available.
> 
> Note that since coherent allocation needs remapping, one must set up
> another device coherent pool by shared-dma-pool and use
> dma_alloc_from_dev_coherent instead for atomic coherent allocation.
> 
> Signed-off-by: Claire Chang <tientzu@xxxxxxxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Tested-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Tested-by: Will Deacon <will@xxxxxxxxxx>

Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
>  include/linux/swiotlb.h | 26 ++++++++++++++++++++++
>  kernel/dma/direct.c     | 49 +++++++++++++++++++++++++++++++----------
>  kernel/dma/swiotlb.c    | 38 ++++++++++++++++++++++++++++++--
>  3 files changed, 99 insertions(+), 14 deletions(-)
> 
> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> index 8d8855c77d9a..a73fad460162 100644
> --- a/include/linux/swiotlb.h
> +++ b/include/linux/swiotlb.h
> @@ -85,6 +85,7 @@ extern enum swiotlb_force swiotlb_force;
>   * @debugfs: The dentry to debugfs.
>   * @late_alloc:      %true if allocated using the page allocator
>   * @force_bounce: %true if swiotlb bouncing is forced
> + * @for_alloc:  %true if the pool is used for memory allocation
>   */
>  struct io_tlb_mem {
>       phys_addr_t start;
> @@ -96,6 +97,7 @@ struct io_tlb_mem {
>       struct dentry *debugfs;
>       bool late_alloc;
>       bool force_bounce;
> +     bool for_alloc;
>       struct io_tlb_slot {
>               phys_addr_t orig_addr;
>               size_t alloc_size;
> @@ -156,4 +158,28 @@ static inline void swiotlb_adjust_size(unsigned long 
> size)
>  extern void swiotlb_print_info(void);
>  extern void swiotlb_set_max_segment(unsigned int);
>  
> +#ifdef CONFIG_DMA_RESTRICTED_POOL
> +struct page *swiotlb_alloc(struct device *dev, size_t size);
> +bool swiotlb_free(struct device *dev, struct page *page, size_t size);
> +
> +static inline bool is_swiotlb_for_alloc(struct device *dev)
> +{
> +     return dev->dma_io_tlb_mem->for_alloc;
> +}
> +#else
> +static inline struct page *swiotlb_alloc(struct device *dev, size_t size)
> +{
> +     return NULL;
> +}
> +static inline bool swiotlb_free(struct device *dev, struct page *page,
> +                             size_t size)
> +{
> +     return false;
> +}
> +static inline bool is_swiotlb_for_alloc(struct device *dev)
> +{
> +     return false;
> +}
> +#endif /* CONFIG_DMA_RESTRICTED_POOL */
> +
>  #endif /* __LINUX_SWIOTLB_H */
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index a92465b4eb12..2de33e5d302b 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -75,6 +75,15 @@ static bool dma_coherent_ok(struct device *dev, 
> phys_addr_t phys, size_t size)
>               min_not_zero(dev->coherent_dma_mask, dev->bus_dma_limit);
>  }
>  
> +static void __dma_direct_free_pages(struct device *dev, struct page *page,
> +                                 size_t size)
> +{
> +     if (IS_ENABLED(CONFIG_DMA_RESTRICTED_POOL) &&
> +         swiotlb_free(dev, page, size))
> +             return;
> +     dma_free_contiguous(dev, page, size);
> +}
> +
>  static struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
>               gfp_t gfp)
>  {
> @@ -86,6 +95,16 @@ static struct page *__dma_direct_alloc_pages(struct device 
> *dev, size_t size,
>  
>       gfp |= dma_direct_optimal_gfp_mask(dev, dev->coherent_dma_mask,
>                                          &phys_limit);
> +     if (IS_ENABLED(CONFIG_DMA_RESTRICTED_POOL) &&
> +         is_swiotlb_for_alloc(dev)) {
> +             page = swiotlb_alloc(dev, size);
> +             if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
> +                     __dma_direct_free_pages(dev, page, size);
> +                     return NULL;
> +             }
> +             return page;
> +     }
> +
>       page = dma_alloc_contiguous(dev, size, gfp);
>       if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
>               dma_free_contiguous(dev, page, size);
> @@ -142,7 +161,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
>               gfp |= __GFP_NOWARN;
>  
>       if ((attrs & DMA_ATTR_NO_KERNEL_MAPPING) &&
> -         !force_dma_unencrypted(dev)) {
> +         !force_dma_unencrypted(dev) && !is_swiotlb_for_alloc(dev)) {
>               page = __dma_direct_alloc_pages(dev, size, gfp & ~__GFP_ZERO);
>               if (!page)
>                       return NULL;
> @@ -155,18 +174,23 @@ void *dma_direct_alloc(struct device *dev, size_t size,
>       }
>  
>       if (!IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED) &&
> -         !IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
> -         !dev_is_dma_coherent(dev))
> +         !IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) && !dev_is_dma_coherent(dev) &&
> +         !is_swiotlb_for_alloc(dev))
>               return arch_dma_alloc(dev, size, dma_handle, gfp, attrs);
>  
>       /*
>        * Remapping or decrypting memory may block. If either is required and
>        * we can't block, allocate the memory from the atomic pools.
> +      * If restricted DMA (i.e., is_swiotlb_for_alloc) is required, one must
> +      * set up another device coherent pool by shared-dma-pool and use
> +      * dma_alloc_from_dev_coherent instead.
>        */
>       if (IS_ENABLED(CONFIG_DMA_COHERENT_POOL) &&
>           !gfpflags_allow_blocking(gfp) &&
>           (force_dma_unencrypted(dev) ||
> -          (IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) && 
> !dev_is_dma_coherent(dev))))
> +          (IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
> +           !dev_is_dma_coherent(dev))) &&
> +         !is_swiotlb_for_alloc(dev))
>               return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
>  
>       /* we always manually zero the memory once we are done */
> @@ -237,7 +261,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
>                       return NULL;
>       }
>  out_free_pages:
> -     dma_free_contiguous(dev, page, size);
> +     __dma_direct_free_pages(dev, page, size);
>       return NULL;
>  }
>  
> @@ -247,15 +271,15 @@ void dma_direct_free(struct device *dev, size_t size,
>       unsigned int page_order = get_order(size);
>  
>       if ((attrs & DMA_ATTR_NO_KERNEL_MAPPING) &&
> -         !force_dma_unencrypted(dev)) {
> +         !force_dma_unencrypted(dev) && !is_swiotlb_for_alloc(dev)) {
>               /* cpu_addr is a struct page cookie, not a kernel address */
>               dma_free_contiguous(dev, cpu_addr, size);
>               return;
>       }
>  
>       if (!IS_ENABLED(CONFIG_ARCH_HAS_DMA_SET_UNCACHED) &&
> -         !IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
> -         !dev_is_dma_coherent(dev)) {
> +         !IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) && !dev_is_dma_coherent(dev) &&
> +         !is_swiotlb_for_alloc(dev)) {
>               arch_dma_free(dev, size, cpu_addr, dma_addr, attrs);
>               return;
>       }
> @@ -273,7 +297,7 @@ void dma_direct_free(struct device *dev, size_t size,
>       else if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_CLEAR_UNCACHED))
>               arch_dma_clear_uncached(cpu_addr, size);
>  
> -     dma_free_contiguous(dev, dma_direct_to_page(dev, dma_addr), size);
> +     __dma_direct_free_pages(dev, dma_direct_to_page(dev, dma_addr), size);
>  }
>  
>  struct page *dma_direct_alloc_pages(struct device *dev, size_t size,
> @@ -283,7 +307,8 @@ struct page *dma_direct_alloc_pages(struct device *dev, 
> size_t size,
>       void *ret;
>  
>       if (IS_ENABLED(CONFIG_DMA_COHERENT_POOL) &&
> -         force_dma_unencrypted(dev) && !gfpflags_allow_blocking(gfp))
> +         force_dma_unencrypted(dev) && !gfpflags_allow_blocking(gfp) &&
> +         !is_swiotlb_for_alloc(dev))
>               return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
>  
>       page = __dma_direct_alloc_pages(dev, size, gfp);
> @@ -310,7 +335,7 @@ struct page *dma_direct_alloc_pages(struct device *dev, 
> size_t size,
>       *dma_handle = phys_to_dma_direct(dev, page_to_phys(page));
>       return page;
>  out_free_pages:
> -     dma_free_contiguous(dev, page, size);
> +     __dma_direct_free_pages(dev, page, size);
>       return NULL;
>  }
>  
> @@ -329,7 +354,7 @@ void dma_direct_free_pages(struct device *dev, size_t 
> size,
>       if (force_dma_unencrypted(dev))
>               set_memory_encrypted((unsigned long)vaddr, 1 << page_order);
>  
> -     dma_free_contiguous(dev, page, size);
> +     __dma_direct_free_pages(dev, page, size);
>  }
>  
>  #if defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_DEVICE) || \
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index ff09341bb9f5..6499cfbfe95f 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -463,8 +463,9 @@ static int swiotlb_find_slots(struct device *dev, 
> phys_addr_t orig_addr,
>  
>       index = wrap = wrap_index(mem, ALIGN(mem->index, stride));
>       do {
> -             if ((slot_addr(tbl_dma_addr, index) & iotlb_align_mask) !=
> -                 (orig_addr & iotlb_align_mask)) {
> +             if (orig_addr &&
> +                 (slot_addr(tbl_dma_addr, index) & iotlb_align_mask) !=
> +                         (orig_addr & iotlb_align_mask)) {
>                       index = wrap_index(mem, index + 1);
>                       continue;
>               }
> @@ -703,3 +704,36 @@ static int __init swiotlb_create_default_debugfs(void)
>  late_initcall(swiotlb_create_default_debugfs);
>  
>  #endif
> +
> +#ifdef CONFIG_DMA_RESTRICTED_POOL
> +struct page *swiotlb_alloc(struct device *dev, size_t size)
> +{
> +     struct io_tlb_mem *mem = dev->dma_io_tlb_mem;
> +     phys_addr_t tlb_addr;
> +     int index;
> +
> +     if (!mem)
> +             return NULL;
> +
> +     index = swiotlb_find_slots(dev, 0, size);
> +     if (index == -1)
> +             return NULL;
> +
> +     tlb_addr = slot_addr(mem->start, index);
> +
> +     return pfn_to_page(PFN_DOWN(tlb_addr));
> +}
> +
> +bool swiotlb_free(struct device *dev, struct page *page, size_t size)
> +{
> +     phys_addr_t tlb_addr = page_to_phys(page);
> +
> +     if (!is_swiotlb_buffer(dev, tlb_addr))
> +             return false;
> +
> +     swiotlb_release_slots(dev, tlb_addr);
> +
> +     return true;
> +}
> +
> +#endif /* CONFIG_DMA_RESTRICTED_POOL */
> -- 
> 2.32.0.288.g62a8d224e6-goog
>