alloc_dma_pages(9)

✨ alloc_dma_pages(9) ✨

okay so bestie, welcome to the alloc_dma_pages page from the Kernel API Manual — yes that's a section 9 page, kernel-internals territory, but don't panic, we got this 💅

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🌸 NAME 🌸

alloc_dma_pages — allocate pages to be used for DMA 🦋

⭐ SYNOPSIS ⭐

struct page * alloc_dma_pages (gfp_t gfp , size_t bytes , u64 phys_limit
, unsigned long attrs );

like, that's the whole signature, no cap. four args, one struct page * coming back at you 🫶

🎀 ARGUMENTS 🎀

• gfp — the GFP flags for the allocation, i.e. the whole vibe of how we're asking the buddy allocator for memory ✨
• bytes — size of the buffer, literally just how many bytes you want 💖
• phys_limit — the maximum allowed physical address of the buffer. it's giving "boundary queen", the pages have to live under this address or we're not happy 🙈
• attrs — DMA attributes for the allocation 🌈

💜 DESCRIPTION 💜

So the way this works: it allocates pages from the buddy allocator. That's step one, main character energy 🎀

And if that's successful, it makes the allocated pages decrypted so that they can be used for DMA. yes bestie, decrypted, that's the whole point — encrypted pages would not slay here, they'd be useless for DMA 😭

🔥 RETURN 🔥

• Decrypted pages — the happy path, we ate 👑
• NULL — on allocation failure, sad but honest 💀
• ERR_PTR(-EAGAIN) — if the allocated physical address was above phys_limit. yeah, it got too high, and yes, that's exactly what phys_limit was there to protect you from 🙈

ngl, memorize the return values fr fr — NULL means the allocation failed, but ERR_PTR(-EAGAIN) means the allocation worked and then the address was out of bounds, so the error tells you something completely different. don't conflate them babes 💅

🦋 SEE ALSO 🦋

the whole ./kernel/dma/swiotlb.c friend group, and honestly? iconic lineup:

• struct io_tlb_slot(9)
• struct io_tlb_area(9)
• swiotlb_adjust_nareas(9)
• limit_nareas(9)
• add_mem_pool(9)
• swiotlb_alloc_tlb(9)
• swiotlb_free_tlb(9)
• swiotlb_alloc_pool(9)
• swiotlb_dyn_alloc(9)
• __swiotlb_find_pool(9)
• swiotlb_del_pool(9)
• swiotlb_dev_init(9)
• swiotlb_align_offset(9)
• swiotlb_search_pool_area(9)
• swiotlb_search_area(9)
• swiotlb_find_slots(9)
• mem_pool_used(9)
• mem_used(9)
• swiotlb_tbl_map_single(9)
• swiotlb_del_transient(9)
• is_swiotlb_allocated(9)
• default_swiotlb_base(9)
• default_swiotlb_limit(9)

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and that's the page, bestie!! 🧚 sign-off time: this one lives in ./kernel/dma and it's dated October 2026 — so when you cite it, cite it cute 💖🍓