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s390: add support for virtually mapped kernel stacks

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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 <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky
2017-09-12 16:37:33 +02:00
parent ff340d2472
commit ce3dc44749
16 changed files with 228 additions and 91 deletions
Download Patch File Download Diff File Expand all files Collapse all files

89
arch/s390/kernel/setup.c
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@@ -49,6 +49,7 @@
#include <linux/crash_dump.h>
#include <linux/memory.h>
#include <linux/compat.h>
#include <linux/start_kernel.h>
#include <asm/ipl.h>
#include <asm/facility.h>
@@ -303,6 +304,78 @@ early_param("vmalloc", parse_vmalloc);
void *restart_stack __section(.data);
unsigned long stack_alloc(void)
{
#ifdef CONFIG_VMAP_STACK
return (unsigned long)
__vmalloc_node_range(STACK_SIZE, STACK_SIZE,
VMALLOC_START, VMALLOC_END,
THREADINFO_GFP,
PAGE_KERNEL, 0, NUMA_NO_NODE,
__builtin_return_address(0));
#else
return __get_free_pages(GFP_KERNEL, STACK_ORDER);
#endif
}
void stack_free(unsigned long stack)
{
#ifdef CONFIG_VMAP_STACK
vfree((void *) stack);
#else
free_pages(stack, STACK_ORDER);
#endif
}
int __init arch_early_irq_init(void)
{
unsigned long stack;
stack = __get_free_pages(GFP_KERNEL, STACK_ORDER);
if (!stack)
panic("Couldn't allocate async stack");
S390_lowcore.async_stack = stack + STACK_INIT_OFFSET;
return 0;
}
static int __init async_stack_realloc(void)
{
unsigned long old, new;
old = S390_lowcore.async_stack - STACK_INIT_OFFSET;
new = stack_alloc();
if (!new)
panic("Couldn't allocate async stack");
S390_lowcore.async_stack = new + STACK_INIT_OFFSET;
free_pages(old, STACK_ORDER);
return 0;
}
early_initcall(async_stack_realloc);
void __init arch_call_rest_init(void)
{
struct stack_frame *frame;
unsigned long stack;
stack = stack_alloc();
if (!stack)
panic("Couldn't allocate kernel stack");
current->stack = (void *) stack;
#ifdef CONFIG_VMAP_STACK
current->stack_vm_area = (void *) stack;
#endif
set_task_stack_end_magic(current);
stack += STACK_INIT_OFFSET;
S390_lowcore.kernel_stack = stack;
frame = (struct stack_frame *) stack;
memset(frame, 0, sizeof(*frame));
/* Branch to rest_init on the new stack, never returns */
asm volatile(
" la 15,0(%[_frame])\n"
" jg rest_init\n"
: : [_frame] "a" (frame));
}
static void __init setup_lowcore(void)
{
struct lowcore *lc;
@@ -329,14 +402,8 @@ static void __init setup_lowcore(void)
PSW_MASK_DAT | PSW_MASK_MCHECK;
lc->io_new_psw.addr = (unsigned long) io_int_handler;
lc->clock_comparator = clock_comparator_max;
lc->kernel_stack = ((unsigned long) &init_thread_union)
lc->nodat_stack = ((unsigned long) &init_thread_union)
+ THREAD_SIZE - STACK_FRAME_OVERHEAD - sizeof(struct pt_regs);
lc->async_stack = (unsigned long)
memblock_virt_alloc(ASYNC_SIZE, ASYNC_SIZE)
+ ASYNC_SIZE - STACK_FRAME_OVERHEAD - sizeof(struct pt_regs);
lc->panic_stack = (unsigned long)
memblock_virt_alloc(PAGE_SIZE, PAGE_SIZE)
+ PAGE_SIZE - STACK_FRAME_OVERHEAD - sizeof(struct pt_regs);
lc->current_task = (unsigned long)&init_task;
lc->lpp = LPP_MAGIC;
lc->machine_flags = S390_lowcore.machine_flags;
@@ -357,8 +424,12 @@ static void __init setup_lowcore(void)
lc->last_update_timer = S390_lowcore.last_update_timer;
lc->last_update_clock = S390_lowcore.last_update_clock;
restart_stack = memblock_virt_alloc(ASYNC_SIZE, ASYNC_SIZE);
restart_stack += ASYNC_SIZE;
/*
* Allocate the global restart stack which is the same for
* all CPUs in cast *one* of them does a PSW restart.
*/
restart_stack = memblock_virt_alloc(STACK_SIZE, STACK_SIZE);
restart_stack += STACK_INIT_OFFSET;
/*
* Set up PSW restart to call ipl.c:do_restart(). Copy the relevant