On Wednesday 22 May 2013, Russell King - ARM Linux wrote: > On Wed, May 22, 2013 at 11:25:36AM +0200, Arnd Bergmann wrote: > > Given the most commonly used functions and a couple of architectures > > I'm familiar with, these are the ones that currently call might_fault() > > > > x86-32 x86-64 arm arm64 powerpc s390 generic > > copy_to_user - x - - - x x > > copy_from_user - x - - - x x > > put_user x x x x x x x > > get_user x x x x x x x > > __copy_to_user x x - - x - - > > __copy_from_user x x - - x - - > > __put_user - - x - x - - > > __get_user - - x - x - - > > > > WTF? > > I think your table is rather screwed - especially on ARM. Tell me - > how can __copy_to_user() use might_fault() but copy_to_user() not when > copy_to_user() is implemented using __copy_to_user() ? Same for > copy_from_user() but the reverse argument - there's nothing special > in our copy_from_user() which would make it do might_fault() when > __copy_from_user() wouldn't. I think something went wrong with formatting of the tabstobs in the table. I've tried to correct it above to the same version I see on the mailing list. > The correct position for ARM is: our (__)?(pu|ge)t_user all use > might_fault(), but (__)?copy_(to|from)_user do not. Neither does > (__)?clear_user. We might want to fix those to use might_fault(). Yes, that sounds like a good idea, especially since they are all implemented out-of-line. For __get_user()/__put_user(), I would probably do the reverse and make them not call might_fault() though, like we do on most other architectures: Look at the object code produced for setup_sigframe for instance, it calls might_fault() around 25 times where one should really be enough. Using __put_user() instead of put_user() is normally an indication that the author of that function has made performance considerations and move the (trivial) access_ok() call out, but now we add a more expensive call instead. Arnd -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>