Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit f5c8b960 authored by Heiko Carstens's avatar Heiko Carstens Committed by Martin Schwidefsky
Browse files

s390/uaccess: use sane length for __strncpy_from_user() 



The average string that is copied from user space to kernel space is
rather short. E.g. booting a system involves about 50.000
strncpy_from_user() calls where the NULL terminated string has an
average size of 27 bytes.

By default our s390 specific strncpy_from_user() implementation
however copies up to 4096 bytes, which is a waste of cpu cycles and
cache lines. Therefore reduce the default length to L1_CACHE_BYTES
(256 bytes), which also reduces the average execution time of
strncpy_from_user() by 30-40%.

Alternatively we could have switched to the generic
strncpy_from_user() implementation, however it turned out that that
variant would be slower than the now optimized s390 variant.

Reported-by: default avatarAl Viro <viro@ZenIV.linux.org.uk>
Reported-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Reviewed-by: default avatarGerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent db55947d

arch/s390/lib/uaccess.c

+2 −2
Original line number Diff line number Diff line
@@ -337,8 +337,8 @@ long __strncpy_from_user(char *dst, const char __user *src, long size) 
		return 0;

	done = 0;

	do {

		offset = (size_t)src & ~PAGE_MASK;

		len = min(size - done, PAGE_SIZE - offset);

		offset = (size_t)src & (L1_CACHE_BYTES - 1);

		len = min(size - done, L1_CACHE_BYTES - offset);

		if (copy_from_user(dst, src, len))

			return -EFAULT;

		len_str = strnlen(dst, len);