From: Jan Kara > Sent: 17 May 2019 09:48 ... > So this last paragraph is not obvious to me as check_copy_size() does a lot > of various checks in CONFIG_HARDENED_USERCOPY case. I agree that some of > those checks don't make sense for PMEM pages but I'd rather handle that by > refining check_copy_size() and check_object_size() functions to detect and > appropriately handle pmem pages rather that generally skip all the checks > in pmem_copy_from/to_iter(). And yes, every check in such hot path is going > to cost performance but that's what user asked for with > CONFIG_HARDENED_USERCOPY... Kees? Except that all the distros enable it by default. So you get the performance cost whether you (as a user) want it or not. I've changed some of our code to use __get_user() to avoid these stupid overheads. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
