Commit ce3dc447 authored by Martin Schwidefsky's avatar Martin Schwidefsky
Browse files

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: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent ff340d24

arch/s390/Kconfig

+2 −0
Original line number Diff line number Diff line
@@ -125,6 +125,7 @@ config S390 
	select HAVE_ARCH_SOFT_DIRTY

	select HAVE_ARCH_TRACEHOOK

	select HAVE_ARCH_TRANSPARENT_HUGEPAGE

	select HAVE_ARCH_VMAP_STACK

	select HAVE_EBPF_JIT if PACK_STACK && HAVE_MARCH_Z196_FEATURES

	select HAVE_CMPXCHG_DOUBLE

	select HAVE_CMPXCHG_LOCAL
@@ -649,6 +650,7 @@ config PACK_STACK 


config CHECK_STACK

	def_bool y

	depends on !VMAP_STACK

	prompt "Detect kernel stack overflow"

	help

	  This option enables the compiler option -mstack-guard and

arch/s390/include/asm/lowcore.h

+2 −2
Original line number Diff line number Diff line
@@ -102,9 +102,9 @@ struct lowcore { 
	__u64	current_task;			/* 0x0338 */

	__u64	kernel_stack;			/* 0x0340 */



	/* Interrupt, panic and restart stack. */

	/* Interrupt, DAT-off and restartstack. */

	__u64	async_stack;			/* 0x0348 */

	__u64	panic_stack;			/* 0x0350 */

	__u64	nodat_stack;			/* 0x0350 */

	__u64	restart_stack;			/* 0x0358 */



	/* Restart function and parameter. */

arch/s390/include/asm/processor.h

+8 −0
Original line number Diff line number Diff line
@@ -162,6 +162,14 @@ struct thread_struct { 


typedef struct thread_struct thread_struct;



/*

 * General size of a stack

 */

#define STACK_ORDER 2

#define STACK_SIZE (PAGE_SIZE << STACK_ORDER)

#define STACK_INIT_OFFSET \

	(STACK_SIZE - STACK_FRAME_OVERHEAD - sizeof(struct pt_regs))



/*

 * Stack layout of a C stack frame.

 */

arch/s390/include/asm/thread_info.h

+0 −3
Original line number Diff line number Diff line
@@ -14,10 +14,7 @@ 
 * Size of kernel stack for each process

 */

#define THREAD_SIZE_ORDER 2

#define ASYNC_ORDER  2



#define THREAD_SIZE (PAGE_SIZE << THREAD_SIZE_ORDER)

#define ASYNC_SIZE  (PAGE_SIZE << ASYNC_ORDER)



#ifndef __ASSEMBLY__

#include <asm/lowcore.h>

arch/s390/kernel/asm-offsets.c

+1 −1
Original line number Diff line number Diff line
@@ -159,7 +159,7 @@ int main(void) 
	OFFSET(__LC_CURRENT, lowcore, current_task);

	OFFSET(__LC_KERNEL_STACK, lowcore, kernel_stack);

	OFFSET(__LC_ASYNC_STACK, lowcore, async_stack);

	OFFSET(__LC_PANIC_STACK, lowcore, panic_stack);

	OFFSET(__LC_NODAT_STACK, lowcore, nodat_stack);

	OFFSET(__LC_RESTART_STACK, lowcore, restart_stack);

	OFFSET(__LC_RESTART_FN, lowcore, restart_fn);

	OFFSET(__LC_RESTART_DATA, lowcore, restart_data);

CRA Git | Maintained and supported by SUSTech CRA and CCSE