Messages in this thread | | | From | David Mosberger <> | Date | Fri, 17 Oct 2003 17:21:13 -0700 | Subject | Re: [RFC] prevent "dd if=/dev/mem" crash |
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>>>>> On Fri, 17 Oct 2003 16:55:43 -0700, Andrew Morton <akpm@osdl.org> said:
>> If we really believe copy_*_user() must correctly handle *all* faults, >> isn't the "p >= __pa(high_memory)" test superfluous?
Andrew> This code was conceived before my time and I don't recall seeing much Andrew> discussion, so this is all guesswork..
Andrew> I'd say that the high_memory test _is_ superfluous and that Andrew> if anyone cared, we would remove it and establish a Andrew> temporary pte against the address if it was outside the Andrew> direct-mapped area. But nobody cares enough to have done Andrew> anything about it.
What about memory-mapped device registers? Isn't all memory physically contiguous on x86 and that's why the "p >= __pa(high_memory)" test saves you from that?
>> On ia64, a read to non-existent physical memory causes the processor >> to time out and take a machine check. I'm not sure it's even possible >> to recover from that.
Andrew> ick. That would be very poor form.
Reasonable people can disagree on that. One philosophy states that if your kernel touches random addresses, it's better to signal a visible error (machine-check) than to risk silent data corruption.
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