Messages in this thread | | | From | Ingo Oeser <> | Subject | Re: mlockall and mmap of IO devices don't mix | Date | Sat, 4 Oct 2003 11:29:25 +0200 |
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On Saturday 04 October 2003 07:47, David S. Miller wrote: > On Fri, 3 Oct 2003 17:27:27 -0700 > > Andrew Morton <akpm@osdl.org> wrote: > > Maybe it's best to not overload VM_RESERVED in this manner, but to always > > mark /dev/mem as VM_IO. > > Just in cast is isn't clear, it should be defined that anything > that sets VM_IO on an mmap() area should prefill the page tables > as a side effect of such a mmap() request. > > Then things like mlockall() have simple semantics on VM_IO area, they > end up being a nop.
It should be already, but the check in get_user_pages() looks wrong and will only disallow VM_IO if you provide space for an page array. It should be unconditional and we are done, because follow_pages will never be called with such vmas.
Putting this check for "forbidden VMAs" into follow_pages is also a good decision, if follow_pages() is called by strange callers not knowing the limitations. kernel/futex.c is such an user, which don't check these in the fast path (does it like wait on hardware triggered futexes there?).
It might be good to add VM_RESERVED check to get_user_pages(), too. These pages are available anyway, so never need to be considered from its users.
Regards
Ingo Oeser
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