Re: arch_timer_edge_cases failures on ampere-one

[Sebastian Ott <sebott@redhat.com>]

On Thu, 10 Apr 2025, Marc Zyngier wrote:
> On Thu, 10 Apr 2025 16:10:43 +0100,
> Sebastian Ott <sebott@redhat.com> wrote:
>>
>> Hey,
>>
>> I'm seeing consistent failures for the arch_timer_edge_cases
>> selftest one ampere-one(x):
>> ==== Test Assertion Failure ====
>>   arm64/arch_timer_edge_cases.c:170: timer_condition == istatus
>>   pid=6277 tid=6277 errno=4 - Interrupted system call
>>      1  0x0000000000403bcf: test_run at arch_timer_edge_cases.c:962
>>      2  0x0000000000401f1f: main at arch_timer_edge_cases.c:1083
>>      3  0x0000ffffa8b2625b: ?? ??:0
>>      4  0x0000ffffa8b2633b: ?? ??:0
>>      5  0x000000000040202f: _start at ??:?
>>   0x1 != 0x0 (timer_condition != istatus)
>>
>> The (first) test that's failing is from test_timers_in_the_past():
>>     /* Set a timer to counter=0 (in the past) */
>>     test_timer_cval(timer, 0, wm, true, DEF_CNT);
>>
>> If I understand this correctly then the timer condition is met, an
>> irq should be raised with the istatus bit from SYS_CNTV_CTL_EL0 set.
>>
>> What the guest gets for SYS_CNTV_CTL_EL0 is 1 (only the enable bit
>> set). KVM also reads 1 in timer_save_state() via
>> read_sysreg_el0(SYS_CNTV_CTL). Is this a HW/FW issue?
>
> My hunch is that this is related to AC03_CPU_14 in [1] (now archived
> locally for future reference...).

Thanks! Your hunch seems to point in the right direction. If the diff is
smaller than 2^63 this is working as expected. I'll try to figure out some
changes that let the test succeed on ampere while still doing meaningful
tests.

Sebastian