Re: How to efficiently handle DMA and cache on ARMv7 ? (was "Isget_user_pages() enough to prevent pages from being swapped out ?")

[Russell King - ARM Linux]

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.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/