From: Oliver Upton oupton@google.com
mainline inclusion from mainline-v5.16-rc1 commit c1153d52c414 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I4QCBG CVE: NA
----------------------
Unfortunately, the architecture provides no means to determine the bit width of the system counter. However, we do know the following from the specification:
- the system counter is at least 56 bits wide - Roll-over time of not less than 40 years
To date, the arch timer driver has depended on the first property, assuming any system counter to be 56 bits wide and masking off the rest. However, combining a narrow clocksource mask with a high frequency counter could result in prematurely wrapping the system counter by a significant margin. For example, a 56 bit wide, 1GHz system counter would wrap in a mere 2.28 years!
This is a problem for two reasons: v8.6+ implementations are required to provide a 64 bit, 1GHz system counter. Furthermore, before v8.6, implementers may select a counter frequency of their choosing.
Fix the issue by deriving a valid clock mask based on the second property from above. Set the floor at 56 bits, since we know no system counter is narrower than that.
[maz: fixed width computation not to lose the last bit, added max delta generation for the timer]
Suggested-by: Marc Zyngier maz@kernel.org Signed-off-by: Oliver Upton oupton@google.com Reviewed-by: Linus Walleij linus.walleij@linaro.org Signed-off-by: Marc Zyngier maz@kernel.org Link: https://lore.kernel.org/r/20210807191428.3488948-1-oupton@google.com Link: https://lore.kernel.org/r/20211017124225.3018098-13-maz@kernel.org Signed-off-by: Daniel Lezcano daniel.lezcano@linaro.org Signed-off-by: Xiongfeng Wang wangxiongfeng2@huawei.com Reviewed-by: Hanjun Guo guohanjun@huawei.com Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com --- drivers/clocksource/arm_arch_timer.c | 34 ++++++++++++++++++++++++---- 1 file changed, 29 insertions(+), 5 deletions(-)
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c index 27d2d93df3f8..447e2a688113 100644 --- a/drivers/clocksource/arm_arch_timer.c +++ b/drivers/clocksource/arm_arch_timer.c @@ -49,6 +49,12 @@ #define CNTV_CVAL_LO 0x30 #define CNTV_CTL 0x3c
+/* + * The minimum amount of time a generic counter is guaranteed to not roll over + * (40 years) + */ +#define MIN_ROLLOVER_SECS (40ULL * 365 * 24 * 3600) + static unsigned arch_timers_present __initdata;
struct arch_timer { @@ -86,6 +92,22 @@ static int __init early_evtstrm_cfg(char *buf) } early_param("clocksource.arm_arch_timer.evtstrm", early_evtstrm_cfg);
+/* + * Makes an educated guess at a valid counter width based on the Generic Timer + * specification. Of note: + * 1) the system counter is at least 56 bits wide + * 2) a roll-over time of not less than 40 years + * + * See 'ARM DDI 0487G.a D11.1.2 ("The system counter")' for more details. + */ +static int arch_counter_get_width(void) +{ + u64 min_cycles = MIN_ROLLOVER_SECS * arch_timer_rate; + + /* guarantee the returned width is within the valid range */ + return clamp_val(ilog2(min_cycles - 1) + 1, 56, 64); +} + /* * Architected system timer support. */ @@ -202,13 +224,11 @@ static struct clocksource clocksource_counter = { .name = "arch_sys_counter", .rating = 400, .read = arch_counter_read, - .mask = CLOCKSOURCE_MASK(56), .flags = CLOCK_SOURCE_IS_CONTINUOUS, };
static struct cyclecounter cyclecounter __ro_after_init = { .read = arch_counter_read_cc, - .mask = CLOCKSOURCE_MASK(56), };
struct ate_acpi_oem_info { @@ -789,7 +809,7 @@ static u64 __arch_timer_check_delta(void) return CLOCKSOURCE_MASK(32); } #endif - return CLOCKSOURCE_MASK(56); + return CLOCKSOURCE_MASK(arch_counter_get_width()); }
static void __arch_timer_setup(unsigned type, @@ -1034,6 +1054,7 @@ struct arch_timer_kvm_info *arch_timer_get_kvm_info(void) static void __init arch_counter_register(unsigned type) { u64 start_count; + int width;
/* Register the CP15 based counter if we have one */ if (type & ARCH_TIMER_TYPE_CP15) { @@ -1060,6 +1081,10 @@ static void __init arch_counter_register(unsigned type) arch_timer_read_counter = arch_counter_get_cntvct_mem; }
+ width = arch_counter_get_width(); + clocksource_counter.mask = CLOCKSOURCE_MASK(width); + cyclecounter.mask = CLOCKSOURCE_MASK(width); + if (!arch_counter_suspend_stop) clocksource_counter.flags |= CLOCK_SOURCE_SUSPEND_NONSTOP; start_count = arch_timer_read_counter(); @@ -1069,8 +1094,7 @@ static void __init arch_counter_register(unsigned type) timecounter_init(&arch_timer_kvm_info.timecounter, &cyclecounter, start_count);
- /* 56 bits minimum, so we assume worst case rollover */ - sched_clock_register(arch_timer_read_counter, 56, arch_timer_rate); + sched_clock_register(arch_timer_read_counter, width, arch_timer_rate); }
static void arch_timer_stop(struct clock_event_device *clk)