Messages in this thread | | | Date | Fri, 7 Aug 2009 10:54:27 +0100 | From | Jamie Lokier <> | Subject | Re: How to efficiently handle DMA and cache on ARMv7 ? (was "Is get_user_pages() enough to prevent pages from being swapped out ?") |
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Russell King - ARM Linux wrote: > On Fri, Aug 07, 2009 at 09:58:30AM +0200, Laurent Pinchart wrote: > > Sorry about this, but I'm not sure to understand the speculative prefetching > > cache issue completely. > > The general case with speculative prefetching is that if memory is > accessible, it can be prefetched. > > In other words, if we mapped devices without NX (non-exec) set, the > CPU can prefetch instructions from devices, causing random read > accesses. Yes, I know it sounds crazy, but that's what I'm told > _can_ happen.
1. Does the architecture not prevent speculative instruction prefetches from crossing a page boundary? It would be handy under the circumstances.
2. Is NX available on all the CPUs with speculative prefetching behaviour? If it is, just use that for device mappings?
-- Jamie
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