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SubjectRe: How to efficiently handle DMA and cache on ARMv7 ? (was "Is get_user_pages() enough to prevent pages from being swapped out ?")
On Tue, Sep 01, 2009 at 03:43:48PM +0200, Laurent Pinchart wrote:
> I might be missing something obvious, but I fail to see how VIVT caches
> could work at all with multiple mappings. If a kernel-allocated buffer
> is DMA'ed to, we certainly want to invalidate all cache lines that store
> buffer data. As the cache doesn't care about physical addresses we thus
> need to invalidate all virtual mappings for the buffer. If the buffer is
> mmap'ed in userspace I don't see how that would be done.

You need to ask MM gurus about that. I don't touch the Linux MM very
often so tend to keep forgetting how it works. However, it does work
for shared mappings of files on CPUs with VIVT caches.


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