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kcsan: Expose core configuration parameters as module params 

This adds early_boot, udelay_{task,interrupt}, and skip_watch as module
params. The latter parameters are useful to modify at runtime to tune
KCSAN's performance on new systems. This will also permit auto-tuning
these parameters to maximize overall system performance and KCSAN's race
detection ability.

None of the parameters are used in the fast-path and referring to them
via static variables instead of CONFIG constants will not affect
performance.

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Qian Cai <cai@lca.pw>
This commit is contained in:
Marco Elver 2020-02-07 19:59:10 +01:00 committed by Ingo Molnar
parent a312013578
commit 80d4c47752
1 changed files with 19 additions and 5 deletions
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24
kernel/kcsan/core.c
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@ -6,6 +6,7 @@
#include <linux/export.h> #include <linux/export.h>
#include <linux/init.h> #include <linux/init.h>
#include <linux/kernel.h> #include <linux/kernel.h>
#include <linux/moduleparam.h>
#include <linux/percpu.h> #include <linux/percpu.h>
#include <linux/preempt.h> #include <linux/preempt.h>
#include <linux/random.h> #include <linux/random.h>
@ -16,6 +17,20 @@
#include "encoding.h" #include "encoding.h"
#include "kcsan.h" #include "kcsan.h"
static bool kcsan_early_enable = IS_ENABLED(CONFIG_KCSAN_EARLY_ENABLE);
static unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
static unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
static long kcsan_skip_watch = CONFIG_KCSAN_SKIP_WATCH;
#ifdef MODULE_PARAM_PREFIX
#undef MODULE_PARAM_PREFIX
#endif
#define MODULE_PARAM_PREFIX "kcsan."
module_param_named(early_enable, kcsan_early_enable, bool, 0);
module_param_named(udelay_task, kcsan_udelay_task, uint, 0644);
module_param_named(udelay_interrupt, kcsan_udelay_interrupt, uint, 0644);
module_param_named(skip_watch, kcsan_skip_watch, long, 0644);
bool kcsan_enabled; bool kcsan_enabled;
/* Per-CPU kcsan_ctx for interrupts */ /* Per-CPU kcsan_ctx for interrupts */
@ -239,9 +254,9 @@ should_watch(const volatile void *ptr, size_t size, int type)
static inline void reset_kcsan_skip(void) static inline void reset_kcsan_skip(void)
{ {
long skip_count = CONFIG_KCSAN_SKIP_WATCH - long skip_count = kcsan_skip_watch -
(IS_ENABLED(CONFIG_KCSAN_SKIP_WATCH_RANDOMIZE) ? (IS_ENABLED(CONFIG_KCSAN_SKIP_WATCH_RANDOMIZE) ?
prandom_u32_max(CONFIG_KCSAN_SKIP_WATCH) : prandom_u32_max(kcsan_skip_watch) :
0); 0);
this_cpu_write(kcsan_skip, skip_count); this_cpu_write(kcsan_skip, skip_count);
} }
@ -253,8 +268,7 @@ static __always_inline bool kcsan_is_enabled(void)
static inline unsigned int get_delay(void) static inline unsigned int get_delay(void)
{ {
unsigned int delay = in_task() ? CONFIG_KCSAN_UDELAY_TASK : unsigned int delay = in_task() ? kcsan_udelay_task : kcsan_udelay_interrupt;
CONFIG_KCSAN_UDELAY_INTERRUPT;
return delay - (IS_ENABLED(CONFIG_KCSAN_DELAY_RANDOMIZE) ? return delay - (IS_ENABLED(CONFIG_KCSAN_DELAY_RANDOMIZE) ?
prandom_u32_max(delay) : prandom_u32_max(delay) :
0); 0);
@ -527,7 +541,7 @@ void __init kcsan_init(void)
* We are in the init task, and no other tasks should be running; * We are in the init task, and no other tasks should be running;
* WRITE_ONCE without memory barrier is sufficient. * WRITE_ONCE without memory barrier is sufficient.
*/ */
if (IS_ENABLED(CONFIG_KCSAN_EARLY_ENABLE)) if (kcsan_early_enable)
WRITE_ONCE(kcsan_enabled, true); WRITE_ONCE(kcsan_enabled, true);
} }