[PATCH v4 01/13] dma-direct: swiotlb: handle swiotlb alloc/free outside __dma_direct_alloc_pages
Mostafa Saleh
smostafa at google.com
Wed May 13 06:57:16 PDT 2026
On Tue, May 12, 2026 at 02:33:56PM +0530, Aneesh Kumar K.V (Arm) wrote:
> Move swiotlb allocation out of __dma_direct_alloc_pages() and handle it in
> dma_direct_alloc() / dma_direct_alloc_pages().
>
> This is needed for follow-up changes that simplify the handling of
> memory encryption/decryption based on the DMA attribute flags.
>
> swiotlb backing pages are already mapped decrypted by
> swiotlb_update_mem_attributes() and rmem_swiotlb_device_init(), so
> dma-direct should not call dma_set_decrypted() on allocation nor
> dma_set_encrypted() on free for swiotlb-backed memory.
>
> Update alloc/free paths to detect swiotlb-backed pages and skip
> encrypt/decrypt transitions for those paths. Keep the existing highmem
> rejection in dma_direct_alloc_pages() for swiotlb allocations.
>
> Only for "restricted-dma-pool", we currently set `for_alloc = true`, while
> rmem_swiotlb_device_init() decrypts the whole pool up front. This pool is
> typically used together with "shared-dma-pool", where the shared region is
> accessed after remap/ioremap and the returned address is suitable for
> decrypted memory access. So existing code paths remain valid.
>
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar at kernel.org>
> ---
> kernel/dma/direct.c | 44 +++++++++++++++++++++++++++++++++++++-------
> 1 file changed, 37 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index ec887f443741..b958f150718a 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -125,9 +125,6 @@ static struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
>
> WARN_ON_ONCE(!PAGE_ALIGNED(size));
>
> - if (is_swiotlb_for_alloc(dev))
> - return dma_direct_alloc_swiotlb(dev, size);
> -
> gfp |= dma_direct_optimal_gfp_mask(dev, &phys_limit);
> page = dma_alloc_contiguous(dev, size, gfp);
> if (page) {
> @@ -204,6 +201,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
> dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs)
> {
> bool remap = false, set_uncached = false;
> + bool mark_mem_decrypt = true;
> struct page *page;
> void *ret;
>
> @@ -250,11 +248,21 @@ void *dma_direct_alloc(struct device *dev, size_t size,
> dma_direct_use_pool(dev, gfp))
> return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
>
> + if (is_swiotlb_for_alloc(dev)) {
> + page = dma_direct_alloc_swiotlb(dev, size);
> + if (page) {
> + mark_mem_decrypt = false;
> + goto setup_page;
> + }
> + return NULL;
> + }
> +
> /* we always manually zero the memory once we are done */
> page = __dma_direct_alloc_pages(dev, size, gfp & ~__GFP_ZERO, true);
> if (!page)
> return NULL;
>
> +setup_page:
> /*
> * dma_alloc_contiguous can return highmem pages depending on a
> * combination the cma= arguments and per-arch setup. These need to be
> @@ -281,7 +289,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
> goto out_free_pages;
> } else {
> ret = page_address(page);
> - if (dma_set_decrypted(dev, ret, size))
> + if (mark_mem_decrypt && dma_set_decrypted(dev, ret, size))
I am ok with that approach, but Jason was mentioning we shouldn’t
special case swiotlb and make the allocator return the memory state
(similar to the dma_page [1]) . I am also OK if you want to merge that
part of my series with is.
[1] https://lore.kernel.org/linux-iommu/20260408194750.2280873-1-smostafa@google.com/
> goto out_leak_pages;
> }
>
> @@ -298,7 +306,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
> return ret;
>
> out_encrypt_pages:
> - if (dma_set_encrypted(dev, page_address(page), size))
> + if (mark_mem_decrypt && dma_set_encrypted(dev, page_address(page), size))
> return NULL;
> out_free_pages:
> __dma_direct_free_pages(dev, page, size);
> @@ -310,6 +318,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
> void dma_direct_free(struct device *dev, size_t size,
> void *cpu_addr, dma_addr_t dma_addr, unsigned long attrs)
> {
> + bool mark_mem_encrypted = true;
> unsigned int page_order = get_order(size);
>
> if ((attrs & DMA_ATTR_NO_KERNEL_MAPPING) &&
> @@ -338,12 +347,15 @@ void dma_direct_free(struct device *dev, size_t size,
> dma_free_from_pool(dev, cpu_addr, PAGE_ALIGN(size)))
> return;
>
> + if (swiotlb_find_pool(dev, dma_to_phys(dev, dma_addr)))
> + mark_mem_encrypted = false;
> +
> if (is_vmalloc_addr(cpu_addr)) {
> vunmap(cpu_addr);
> } else {
> if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_CLEAR_UNCACHED))
> arch_dma_clear_uncached(cpu_addr, size);
> - if (dma_set_encrypted(dev, cpu_addr, size))
> + if (mark_mem_encrypted && dma_set_encrypted(dev, cpu_addr, size))
> return;
> }
>
> @@ -359,6 +371,19 @@ struct page *dma_direct_alloc_pages(struct device *dev, size_t size,
> if (force_dma_unencrypted(dev) && dma_direct_use_pool(dev, gfp))
> return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
>
> + if (is_swiotlb_for_alloc(dev)) {
> + page = dma_direct_alloc_swiotlb(dev, size);
> + if (!page)
> + return NULL;
> +
> + if (PageHighMem(page)) {
My understanding is that rmem_swiotlb_device_init() asserts that there
is no PageHighMem()? Also a similar check doesn’t exist in
dma_direct_alloc().
Thanks,
Mostafa
> + swiotlb_free(dev, page, size);
> + return NULL;
> + }
> + ret = page_address(page);
> + goto setup_page;
> + }
> +
> page = __dma_direct_alloc_pages(dev, size, gfp, false);
> if (!page)
> return NULL;
> @@ -366,6 +391,7 @@ struct page *dma_direct_alloc_pages(struct device *dev, size_t size,
> ret = page_address(page);
> if (dma_set_decrypted(dev, ret, size))
> goto out_leak_pages;
> +setup_page:
> memset(ret, 0, size);
> *dma_handle = phys_to_dma_direct(dev, page_to_phys(page));
> return page;
> @@ -378,13 +404,17 @@ void dma_direct_free_pages(struct device *dev, size_t size,
> enum dma_data_direction dir)
> {
> void *vaddr = page_address(page);
> + bool mark_mem_encrypted = true;
>
> /* If cpu_addr is not from an atomic pool, dma_free_from_pool() fails */
> if (IS_ENABLED(CONFIG_DMA_COHERENT_POOL) &&
> dma_free_from_pool(dev, vaddr, size))
> return;
>
> - if (dma_set_encrypted(dev, vaddr, size))
> + if (swiotlb_find_pool(dev, page_to_phys(page)))
> + mark_mem_encrypted = false;
> +
> + if (mark_mem_encrypted && dma_set_encrypted(dev, vaddr, size))
> return;
> __dma_direct_free_pages(dev, page, size);
> }
> --
> 2.43.0
>
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