ERRATUM_858921 is broken on 5.15 kernel
Yogesh Lal
quic_ylal at quicinc.com
Sun Jan 8 22:52:20 PST 2023
On 1/5/2023 7:52 PM, Marc Zyngier wrote:
> On Thu, 05 Jan 2023 13:33:48 +0000,
> Yogesh Lal <quic_ylal at quicinc.com> wrote:
>> Hi,
>>
>> We are observing issue on A73 core where ERRATUM_858921 is broken.
>>
>> On 5.15 kernel arch_timer_enable_workaround is set by reading
>> arm64_858921_read_cntpct_el0 and arm64_858921_read_cntvct_el0 during
>> timer register using following path.
> Have you checked whether the issue is still present on 6.1?
yes, its preset there as well.
>
>> arch_timer_enable_workaround->atomic_set(&timer_unstable_counter_workaround_in_use,
>> 1);
>>
>> [code snap]
>> 564 static
>> 565 void arch_timer_enable_workaround(const struct
>> arch_timer_erratum_workaround *wa,
>> 566 bool local)
>> 567 {
>> 568 int i;
>> 569
>> 570 if (local) {
>> 571 __this_cpu_write(timer_unstable_counter_workaround, wa);
>> 572 } else {
>> 573 for_each_possible_cpu(i)
>> 574 per_cpu(timer_unstable_counter_workaround, i) = wa;
>> 575 }
>> 576
>> 577 if (wa->read_cntvct_el0 || wa->read_cntpct_el0)
>> 578 atomic_set(&timer_unstable_counter_workaround_in_use, 1);
>>
>>
>> and based on above workaround enablement , appropriate function to get
>> counter is used.
>>
>> 1008 static void __init arch_counter_register(unsigned type)
>> 1009 {
>> 1010 u64 start_count;
>> 1011
>> 1012 /* Register the CP15 based counter if we have one */
>> 1013 if (type & ARCH_TIMER_TYPE_CP15) {
>> 1014 u64 (*rd)(void);
>> 1015
>> 1016 if ((IS_ENABLED(CONFIG_ARM64) && !is_hyp_mode_available()) ||
>> 1017 arch_timer_uses_ppi == ARCH_TIMER_VIRT_PPI) {
>> 1018 if (arch_timer_counter_has_wa())
>> 1019 rd = arch_counter_get_cntvct_stable;
>> 1020 else
>> 1021 rd = arch_counter_get_cntvct;
>> 1022 } else {
>> 1023 if (arch_timer_counter_has_wa())
>> 1024 rd = arch_counter_get_cntpct_stable;
>> 1025 else
>> 1026 rd = arch_counter_get_cntpct;
>> 1027 }
>> [snap]
>> 1043 /* 56 bits minimum, so we assume worst case rollover */
>> 1044 sched_clock_register(arch_timer_read_counter, 56, arch_timer_rate);
>>
>>
>> As our boot cores are not impacted by errata sched_clock_register()
>> will register !arch_timer_counter_has_wa() callback.
>>
>> Now when errata impacted core boots up and sched_clock_register
>> already register will !arch_timer_counter_has_wa() path.
>> As sched_clock_register is not per_cpu bases so
>> arch_timer_read_counter will always point to
>> !arch_timer_counter_has_wa() function calls.
> Please try the following hack, only compile tested as I do not have
> access to any affected HW, and report whether this solves your issue
> or not. Note that this is based on 6.2-rc2.
tested it on affected h/w but looks like sched_clock is still pointing
to !arch_timer_counter_has_wa() function calls,
may be due to sched_clock_register will register once during non errata
impacted core booting.
1007 static void __init arch_counter_register(unsigned type)
1008 {
[snap]
1043 /* 56 bits minimum, so we assume worst case rollover */
1044 sched_clock_register(arch_timer_read_counter, 56, arch_timer_rate);
Also update_clock_read_data will called with
!arch_timer_counter_has_wa() read function calls.
153 void sched_clock_register(u64 (*read)(void), int bits, unsigned long
rate)
[snap]
183 cd.actual_read_sched_clock = read;
184
185 rd.read_sched_clock = read;
186 rd.sched_clock_mask = new_mask;
187 rd.mult = new_mult;
188 rd.shift = new_shift;
189 rd.epoch_cyc = new_epoch;
190 rd.epoch_ns = ns;
191
192 update_clock_read_data(&rd);
> Thanks,
>
> M.
>
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index e09d4427f604..a7cf0a2c86d3 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -230,6 +230,28 @@ static u64 arch_counter_read_cc(const struct cyclecounter *cc)
> return arch_timer_read_counter();
> }
>
> +static bool arch_timer_counter_has_wa(void);
> +
> +static u64 (*arch_counter_get_read_fn(void))(void)
> +{
> + u64 (*rd)(void);
> +
> + if ((IS_ENABLED(CONFIG_ARM64) && !is_hyp_mode_available()) ||
> + arch_timer_uses_ppi == ARCH_TIMER_VIRT_PPI) {
> + if (arch_timer_counter_has_wa())
> + rd = arch_counter_get_cntvct_stable;
> + else
> + rd = arch_counter_get_cntvct;
> + } else {
> + if (arch_timer_counter_has_wa())
> + rd = arch_counter_get_cntpct_stable;
> + else
> + rd = arch_counter_get_cntpct;
> + }
> +
> + return rd;
> +}
> +
> static struct clocksource clocksource_counter = {
> .name = "arch_sys_counter",
> .id = CSID_ARM_ARCH_COUNTER,
> @@ -571,8 +593,10 @@ void arch_timer_enable_workaround(const struct arch_timer_erratum_workaround *wa
> per_cpu(timer_unstable_counter_workaround, i) = wa;
> }
>
> - if (wa->read_cntvct_el0 || wa->read_cntpct_el0)
> + if (wa->read_cntvct_el0 || wa->read_cntpct_el0) {
> atomic_set(&timer_unstable_counter_workaround_in_use, 1);
> + arch_timer_read_counter = arch_counter_get_read_fn();
> + }
>
> /*
> * Don't use the vdso fastpath if errata require using the
> @@ -641,7 +665,7 @@ static bool arch_timer_counter_has_wa(void)
> #else
> #define arch_timer_check_ool_workaround(t,a) do { } while(0)
> #define arch_timer_this_cpu_has_cntvct_wa() ({false;})
> -#define arch_timer_counter_has_wa() ({false;})
> +static bool arch_timer_counter_has_wa(void) { return false; }
> #endif /* CONFIG_ARM_ARCH_TIMER_OOL_WORKAROUND */
>
> static __always_inline irqreturn_t timer_handler(const int access,
> @@ -1079,22 +1103,7 @@ static void __init arch_counter_register(unsigned type)
>
> /* Register the CP15 based counter if we have one */
> if (type & ARCH_TIMER_TYPE_CP15) {
> - u64 (*rd)(void);
> -
> - if ((IS_ENABLED(CONFIG_ARM64) && !is_hyp_mode_available()) ||
> - arch_timer_uses_ppi == ARCH_TIMER_VIRT_PPI) {
> - if (arch_timer_counter_has_wa())
> - rd = arch_counter_get_cntvct_stable;
> - else
> - rd = arch_counter_get_cntvct;
> - } else {
> - if (arch_timer_counter_has_wa())
> - rd = arch_counter_get_cntpct_stable;
> - else
> - rd = arch_counter_get_cntpct;
> - }
> -
> - arch_timer_read_counter = rd;
> + arch_timer_read_counter = arch_counter_get_read_fn();
> clocksource_counter.vdso_clock_mode = vdso_default;
> } else {
> arch_timer_read_counter = arch_counter_get_cntvct_mem;
>
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