Commit c25ca0c2 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'timers_urgent_for_v6.13_rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull timer fix from Borislav Petkov:

 - Handle the case where clocksources with small counter width can,
   in conjunction with overly long idle sleeps, falsely trigger the
   negative motion detection of clocksources

* tag 'timers_urgent_for_v6.13_rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  clocksource: Make negative motion detection more robust
parents 84262262 76031d95

include/linux/clocksource.h

+2 −0
Original line number Diff line number Diff line
@@ -49,6 +49,7 @@ struct module; 
 * @archdata:		Optional arch-specific data

 * @max_cycles:		Maximum safe cycle value which won't overflow on

 *			multiplication

 * @max_raw_delta:	Maximum safe delta value for negative motion detection

 * @name:		Pointer to clocksource name

 * @list:		List head for registration (internal)

 * @freq_khz:		Clocksource frequency in khz.
@@ -109,6 +110,7 @@ struct clocksource { 
	struct arch_clocksource_data archdata;

#endif

	u64			max_cycles;

	u64			max_raw_delta;

	const char		*name;

	struct list_head	list;

	u32			freq_khz;

kernel/time/clocksource.c

+10 −1
Original line number Diff line number Diff line
@@ -24,7 +24,7 @@ static void clocksource_enqueue(struct clocksource *cs); 


static noinline u64 cycles_to_nsec_safe(struct clocksource *cs, u64 start, u64 end)

{

	u64 delta = clocksource_delta(end, start, cs->mask);

	u64 delta = clocksource_delta(end, start, cs->mask, cs->max_raw_delta);



	if (likely(delta < cs->max_cycles))

		return clocksource_cyc2ns(delta, cs->mult, cs->shift);
@@ -993,6 +993,15 @@ static inline void clocksource_update_max_deferment(struct clocksource *cs) 
	cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,

						cs->maxadj, cs->mask,

						&cs->max_cycles);



	/*

	 * Threshold for detecting negative motion in clocksource_delta().

	 *

	 * Allow for 0.875 of the counter width so that overly long idle

	 * sleeps, which go slightly over mask/2, do not trigger the

	 * negative motion detection.

	 */

	cs->max_raw_delta = (cs->mask >> 1) + (cs->mask >> 2) + (cs->mask >> 3);

}



static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)

kernel/time/timekeeping.c

+4 −2
Original line number Diff line number Diff line
@@ -755,7 +755,8 @@ static void timekeeping_forward_now(struct timekeeper *tk) 
	u64 cycle_now, delta;



	cycle_now = tk_clock_read(&tk->tkr_mono);

	delta = clocksource_delta(cycle_now, tk->tkr_mono.cycle_last, tk->tkr_mono.mask);

	delta = clocksource_delta(cycle_now, tk->tkr_mono.cycle_last, tk->tkr_mono.mask,

				  tk->tkr_mono.clock->max_raw_delta);

	tk->tkr_mono.cycle_last = cycle_now;

	tk->tkr_raw.cycle_last  = cycle_now;
@@ -2230,7 +2231,8 @@ static bool timekeeping_advance(enum timekeeping_adv_mode mode) 
		return false;



	offset = clocksource_delta(tk_clock_read(&tk->tkr_mono),

				   tk->tkr_mono.cycle_last, tk->tkr_mono.mask);

				   tk->tkr_mono.cycle_last, tk->tkr_mono.mask,

				   tk->tkr_mono.clock->max_raw_delta);



	/* Check if there's really nothing to do */

	if (offset < real_tk->cycle_interval && mode == TK_ADV_TICK)

kernel/time/timekeeping_internal.h

+4 −4
Original line number Diff line number Diff line
@@ -30,15 +30,15 @@ static inline void timekeeping_inc_mg_floor_swaps(void) 


#endif



static inline u64 clocksource_delta(u64 now, u64 last, u64 mask)

static inline u64 clocksource_delta(u64 now, u64 last, u64 mask, u64 max_delta)

{

	u64 ret = (now - last) & mask;



	/*

	 * Prevent time going backwards by checking the MSB of mask in

	 * the result. If set, return 0.

	 * Prevent time going backwards by checking the result against

	 * @max_delta. If greater, return 0.

	 */

	return ret & ~(mask >> 1) ? 0 : ret;

	return ret > max_delta ? 0 : ret;

}



/* Semi public for serialization of non timekeeper VDSO updates. */