From ce3dc447493ff4186b192b38d723ab5e8c1eb52f Mon Sep 17 00:00:00 2001 From: Martin Schwidefsky Date: Tue, 12 Sep 2017 16:37:33 +0200 Subject: s390: add support for virtually mapped kernel stacks With virtually mapped kernel stacks the kernel stack overflow detection is now fault based, every stack has a guard page in the vmalloc space. The panic_stack is renamed to nodat_stack and is used for all function that need to run without DAT, e.g. memcpy_real or do_start_kdump. The main effect is a reduction in the kernel image size as with vmap stacks the old style overflow checking that adds two instructions per function is not needed anymore. Result from bloat-o-meter: add/remove: 20/1 grow/shrink: 13/26854 up/down: 2198/-216240 (-214042) In regard to performance the micro-benchmark for fork has a hit of a few microseconds, allocating 4 pages in vmalloc space is more expensive compare to an order-2 page allocation. But with real workload I could not find a noticeable difference. Acked-by: Heiko Carstens Signed-off-by: Martin Schwidefsky --- arch/s390/kernel/head64.S | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) (limited to 'arch/s390/kernel/head64.S') diff --git a/arch/s390/kernel/head64.S b/arch/s390/kernel/head64.S index b31dfb102700..57bba24b1c27 100644 --- a/arch/s390/kernel/head64.S +++ b/arch/s390/kernel/head64.S @@ -36,9 +36,7 @@ ENTRY(startup_continue) # larl %r14,init_task stg %r14,__LC_CURRENT - larl %r15,init_thread_union+THREAD_SIZE - stg %r15,__LC_KERNEL_STACK # set end of kernel stack - aghi %r15,-STACK_FRAME_OVERHEAD + larl %r15,init_thread_union+THREAD_SIZE-STACK_FRAME_OVERHEAD # # Early setup functions that may not rely on an initialized bss section, # like moving the initrd. Returns with an initialized bss section. -- cgit v1.2.3