Messages in this thread | ![/](/images/icornerl.gif) | | Date | Thu, 29 Feb 2024 14:33:46 +0100 | From | Christoph Hellwig <> | Subject | Re: [PATCH v5 6/6] swiotlb: Remove pointless stride adjustment for allocations >= PAGE_SIZE |
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On Thu, Feb 29, 2024 at 07:36:05AM +0000, Michael Kelley wrote: > If there *is* a requirement for page alignment of page-size-or-greater > requests, even when alloc_align_mask and min_align_mask are zero, > we need to think about how to do that correctly, as that requirement > is no longer met after Patch 1 of this series.
It has been historical behavior that all dma allocations are page aligned (including in fact smaller than page sized ones that get rounded up to a page size). The documentation actually (incorretly) states an even stronger guarantee:
"The CPU virtual address and the DMA address are both guaranteed to be aligned to the smallest PAGE_SIZE order which is greater than or equal to the requested size. This invariant exists (for example) to guarantee that if you allocate a chunk which is smaller than or equal to 64 kilobytes, the extent of the buffer you receive will not cross a 64K boundary."
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